Tag Archives: thinset mortar

stained glass shards in buckets

How to Make a Stepping Stone with Scrap Glass

If you work with stained glass over time you can end up with buckets full of scrap. When the pieces start getting too small and irregular, or if there’s just too much of it, you can used them in a stepping stone. This tutorial demonstrates how to make a stepping stone with an abstract pattern. You can also use tiles instead of stained glass scraps.

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Lisa Jones Patio Mosaic

Patio Mosaic Alternatives

Patios are excellent locations for mosaics, but the patio floor itself is not as good a surface for a mosaic as a surrounding wall or brick planter would be. The main reason is simple: metal patio furniture will crack and crush glass tile, and glass is the preferred material because it is frost proof, economical, and comes in many colors. Also, the floor of the patio is not as visible as a nearby vertical surface is likely to be, especially when furniture, grills, and the usual patio accessories are present.

Recently artist Lisa Jones emailed me some photos of her patio mosaic, and I was taken with it in spite of my preference for designs that use free-form placement of pieces of tile instead of gridded patterns of whole tile.

Lisa Jones Patio Mosaic right side

Lisa Jones Patio Mosaic right side continues with the garden theme and flower and bee motifs.

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Mosaic Baptismal Font

Artist Sondra Jonson recently completed a mosaic baptismal font for St. James Catholic Church using our gold glass mosaic and metallic glass tile and vitreous glass tile, and it turned out really well. Religious architecture is supposed to be instructive and inspiring, and so Sondra used a spiral galaxy motif for the bottom of the font and a night sky with stars for the insides of the walls to convey the cosmic significance of the sacrament of baptism.

Mosaic Baptismal Font

Mosaic Baptismal Font at St James Catholic Church uses a spiral galaxy motif for the bottom and a field of stars for the insides of the walls.

Laying Up The Mosaic Design

Sondra laid up the mosaic design using mosaic mounting tape, which is recommended instead of fiberglass mesh for outdoor and wet mosaics because glue is used to attach tile to mesh, and glue is vulnerable to moisture. If you use mosaic mounting tape to pick your design up by the faces of the tiles, then you can press the tile directly into the thinset mortar. If you would like to know more, I wrote some instructions for laying up mosaic designs on contact paper and then picking it up with mosaic mounting tape.

Mosaic design divided into sections

Mosaic design divided into sections for ease of handling. Note the use of cardboard “trays” to lift the sheets without bending. The clear mosaic mounting tape is on the front of the tiles.

Square Sheets?

Whether you use mesh or mounting tape, you need to minimize the amount of bending and flexing because that can make tiles pop off the sheets. You can use cardboard or plywood panels to lift and transport the sheets. Note that Sondra’s sheets aren’t square for the simple reason that radial sections made more sense than squares because the area to be covered was hexagonal.


Mosaic Font Bottom Detail

Mosaic Font Bottom Detail shows how the design was laid up in one piece before being cut into manageable sheets.

Write Down The Names Of Your Tiles!

We recommend that artists save their invoice and glue a small piece of tile next to each product listed on the invoice. That way, you know what you used and where you bought it and when. The date of purchase is as important as the color name and supplier because tile varies by batch, and manufacturers revise their products all the time. Sondra wisely made a sample board for the materials used in the baptismal font in case it ever needs to be repaired or a future client wants to use some of the same materials,

Mosaic Palette Sample Board

Mosaic Palette Sample Board for the baptismal font project.

I cannot imagine installing a large public art project without documenting what materials and sources you used. Even if a product is discontinued or revised, which does happen, you or your client will still have the name and the brand and samples for a photo if you make a board like this on for the project. That is a better starting point for finding a replacement from a different supplier than blurry detail shots cropped from photos of the project, which is what people email us all too often.

Mosaic Installation

This mosaic was installed using thinset mortar, which is recommended for all mosaics in pools and fountains and other wet locations. I wrote some instructions for using thinset mortar for detailed mosaic artwork if you need to know more for your project.

Mosaic Baptismal Font wall detail

Mosaic Baptismal Font wall detail being installed with thinset mortar.

The Artist Surveys Work In Progress

Artist Sondra Johnson mosaic in progress

Artist Sondra Johnson working on the mosaic design for the bottom of the baptismal font.

Mosaic Pizza Oven

Mosaic Fireplace and Oven Surrounds: The Basics

A couple of years ago, I wrote a page explaining how glass, ceramic, and stone tiles can be used for mosaic fireplace surrounds and how the tiles should be mounted with thinset mortar or white PVA (polyvinyl acetate) adhesives such as Weldbond. But we are talking about the SURROUNDS, not inside the firebox. For inside the firebox, your need to use refractory materials (brick or stone) that can resist combustion temperatures. For the hearth, the issue is not temperature resistance so much as impact resistance: It doesn’t make sense to use glass tiles that are easily cracked by a metal poker or small tiles that are easily knocked loose. Stylistic concerns should never outweigh performance and durability, else the work won’t look good for long.

Mosaic Pizza Oven

Mosaic Pizza Oven by artist Kristina Young with octopus tentacle motif. Seafood and sea life and undersea scenes were common themes of Roman mosaic.

Problems with a Mosaic Pizza Oven

Recently, artist Kristina Young emailed me concerning a problem she was having with a mosaic she installed on the outer surface of an Italian pizza oven. The problem was that the mosaic was cracking over the door of the oven, and that caused me some concern because that should not happen with traditional fireplaces and pizza ovens constructed with brick or stone, and I have been telling people for years that there was no reason why they could not put mosaics on these surfaces in spite of the heat. Had I overlooked some basic technical principle and made recommendations that could ruin hundreds of people’s projects? The engineer in me became completely paranoid, and I could not wait for Kristina to email me back with answers to my initial questions.

Spoiler Alert: The good news is that the cracking is reparable and that the cracking is by the iron frame of the oven door, not the masonry elements of the oven itself, which means that there is no reason to expect similar problems with traditional fireplaces and ovens that are made from all stone or brick or concrete.

The Case of the Cracking Mosaic

cracking mosaic detail

Detail shot showing crack in brand new mosaic covering the exterior of masonry pizza oven. The location of this crack is significant: It started  right above the iron frame of the oven door.

When Kristina first contacted me, she was concerned that the cracking might have been caused by heating the oven not long after the mosaic was completed. That is a potential issue because thinset mortar takes time to harden, and like concrete, it hardens by bonding moisture not by drying out. (Concrete, mortars, grouts, and other portland cement products will be soft and crumbly if they are dried out by heat or dried air. They need to incorporate the water mixed into them, not have it removed artificially.)

Humidify, Don’t Heat

I don’t think that the oven was heated prematurely or that premature heating caused the cracking. The crack is location specific, and if the mortar was artificially dried out before it could harden, then the problem would be seen all over the mosaic in the form of cracks and missing tiles. That being said, I would avoid heating fireplaces and ovens for several days after a mosaic has been applied to them and grouted. The usual practice is to run humidifiers near a new mosaic to protect them from AC or central heat –not build a fire under them!

Thermal Expansion

Except for the notable exception of ice, most materials expand when they are heated. (Water expands when it freezes, and that is why ice floats: it is less dense than the water beneath it.) The problem with thermal expansion is that materials expand at different rates, and metals like iron expand more rapidly than stone, brick, and concrete. Kristina had already told me that the crack started on the front of the oven just over the door, and so as soon as she sent me a picture of the oven showing that the door had an iron frame, it was obvious to me why the crack had started there: The glass and mortar mosaic expands at roughly the same rate as the brick and concrete oven underneath it, but the iron door frame and the other iron structural elements expand even faster. They push the mosaic up like a shell on the outside of the oven, and when the oven and frame cool back down and contract, the crack appears.

The Right Repair Materials

An “expansion joint” spontaneously forming in the middle of your mosaic might have most people panicking and thinking of repairing the crack with a flexible material such as caulk. Caulk is problematic because it will not age well. It will yellow and shrink and crack. It will look more and more like the synthetic material that it is, a material that looks out of place on tile, a material which does not age.

Grout could be used to fill the crack. After all, grout is the concrete product that is used to grout gaps between tiles in the first place. However, thinset mortar is a better choice because it is harder and tougher and more adhering than grout,, and it can tolerate slight displacement (movement) while grout cannot. In fact, it would have been best if the entire mosaic had been “grouted” with thinset. I suspect that heating and cooling the oven in cycles over time may cause other cracks to appear or reappear, and these should have thinset rubbed into them as needed. Hopefully any new cracks or reappearing cracks will be smaller, but in any case, thinset is better equipped to withstand the stresses of expanding and contracting than grout.

Mosaic crack repaired with thinset mortar

Mosaic crack being repaired with thinset mortar. The mortar is spread on and worked into the cracks and wiped off just like grout. Thinset is superior to grout because it is harder and tougher and can tolerate slight movement.

Aesthetics and Authenticity

Think of high-end restaurants in reclaimed urban warehouse spaces: the exposed beams, the plaster chipped away in places to reveal the stone walls underneath, the different architectural elements like fire doors and hoists deliberately left in place to call attention to the space’s past industrial use.

To me, one of the more interesting things you can see in the mosaics of Mexico and the Mediterranean basin are the repairs that have been made to these over the years following earthquakes and other damage. I’m not thinking of the repairs that were made in modern times by archaeologists or professional conservators sparing no expense to make the mosaic look as if the damage had never occurred. I’m thinking of repairs made in the distant past by inexpert hands or by people with limited access to materials. I’m thinking of repairs like mortar-filled voids and replacement tiles of not-quite-the-right color and how you can sometimes see a series of these inexact repairs apparently made at different times in response to different injuries. To me, these inexact repairs more than anything else give me a sense of how ancient the mosaics are and how much history they have witnessed, endured even: earthquakes, fires, wars with slings and arrows, wars with bullets and bombs.

A large part of the ethos of mosaic art is it being an enduring relic of the past. If I were wanting to design a mosaic to look like an old relic, I might consider deliberately including mortar-filled voids and cracks to simulate past damage or maybe re-mosaicing some of these regions with coarser tile. With that in mind, is a crack appearing in a new mosaic in an Italian or Mexican restaurant a problem or a windfall? I’m thinking not. I’m thinking of the kid who deliberately scuffs up his new baseball glove so that it doesn’t look the unused glove of a rookie.




Mosaic Transfer Instructions

Yesterday I wrote up some recommendations and instructions for Outdoor School Mosaics that focused on a project where each child made a mosaic stepping stone on a paver to be arranged in a crazy quilt design. I forgot to clarify that those instructions were written for younger students and beginners needing to play around with tile and get some basic experience forming tile into patterns and shapes. After all, it doesn’t make sense to have young children trying to copy the work of an experienced mosaic artist before they have had the benefit of handling tile long enough to make a simple triangle or smiley face.

More Sophisticated Designs

If you wanted to use make a more sophisticated design with smaller pieces of tile or to render an image, you could adapt that same method and add just a few steps. I have the steps numbered below, but here is a summary of what would be different: Before you covered the cardboard square with contact paper (sticky side out), you would draw your pattern on the cardboard or tape the pattern to the cardboard. Once you position all your tile on the pattern covered in contact paper, you would use some mosaic mounting film to pick it up off the cardboard/contact paper. Then the mosaic could be pressed onto a paver or stepping stone coated with thinset. Once the thinset hardens, the mounting film is peeled off and the mosaic is grouted. This method allows you to lay up very complicated designs in advance of transferring it all at once to the cement.

Pavers vs. Molds

Note that here I am talking about using thinset mortar to attach a mosaic design to an existing stepping stone or paver or flagstone. If you need instructions for how to use a stepping stone mold to press tiles into wet concrete (or pour wet concrete over a mosaic design mounted on contact paper at the bottom of a mold), then read my article on Mosaic Stepping Stone Instructions.

Stepping Stone Transfer Instructions

  1. Cut out a square of cardboard the same size as your stepping stone or paver. If you want to use an irregularly shaped piece of flagstone as your mosaic base, you can cut out a piece of cardboard in the same shape as the flagstone. Just lay the flagstone on the cardboard and trace around it.
  2. Draw your mosaic pattern on the cardboard or on a piece of paper taped to the cardboard.
  3. Wrap the cardboard pattern with clear contact paper with the STICKY SIDE OUT. The sticky contact paper keeps the tiles from sliding around as you position them on the pattern.
  4. Use mosaic mounting tape (or clear packing tape) to pick the mosaic up off the cardboard pattern.
  5. Coat the paver or stepping stone or flagstone with a thin layer of thinset mortar. Smear it around to make sure the surface is wetted thoroughly and then scrape off the excess. You only need a layer about 1/16 inch thick. A little more won’t hurt, and it doesn’t have to be exact, but too much can be a little messy if you press down of the mosaic and squeeze it out the sides.
  6. Press the mosaic into the thinset. It may be easier to lay the mosaic on a table (with the mounting tape side down) and lower the thinset-covered stone onto the sheet of tile.
  7. Allow the thinset to harden for 24+ hours.
  8. Peel off the mosaic mounting tape.
  9. Grout the mosaic with additional thinset if needed. It is better to use more thinset instead of grout because it will match the color of any thinset that pressed up between the tiles when you mounted the mosaic. If you use grout, then the color probably won’t be exactly the same, and your mosaic will look like you grouted it with two different types of concrete. Often no additional grout is needed because enough thinset squeezes up between the tiles during mounting.
  10. Clean any grout residue or haze from the face of the mosaic by buffing with a clean cloth.
  11. Allow the grout to cure for 2 or 3 days and then seal the finished mosaic with a tile and grout sealer purchased from a local building material store.

For more information on using clear contact paper and mosaic mounting tape to lay up and transfer mosaic designs, read my article on Mounting A Mosaic On Clear Adhesive Film. If the cost of mosaic mounting tape is too high, or if you don’t need a whole roll, then you can use clear packing tape as a substitute.

Terracotta Flower Pots Mosaic Warning

Terracotta flower pots are highly susceptible to freeze damage because the material is extremely porous. Moisture seeps into the tiny pores, freezes and expands, and then the surface flakes off as shown below. However, it is possible to use terracotta as a mosaic base provided the mosaic is mounted correctly and the artist understands the limitations of the material.


Terracotta flower pots are highly vulnerable to freeze damage because they are soft and porous. The damage could have been minimized by sealing the pot inside and out with a tile and grout sealer.

Minimizing Damage To Terracotta Flower Pots

Freeze damage can be minimized by sealing the flower pot inside and out with a tile and grout sealer from a local building material store. Tile and grout sealers are silicone products that plug tiny pores and prevent moisture penetration. They can also interfere with bonding, so we recommend sealing the flower pot AFTER your mosaic is complete. Note that even if you do seal a terracotta pot very well with multiple applications of sealant, it still won’t last as long as a concrete pot would.

Concrete Pots Are Preferred

A terracotta pot might be an acceptable base for an abstract mosaic quickly made from random colorful tile, but detailed mosaic designs take more time and effort than that, and they deserve a more durable base. Concrete flower pots and planters are available at most lawn and garden centers, and whatever extra cost is well worth it. A single winter of hard freezes can totally destroy a terracotta flower pot left outdoors. Also terracotta is also easily broken and cracked during normal use.

Sure you might already have terracotta pots at home that you could use for free, but how much money are you saving if the mosaic doesn’t last six months? Once you take the time to mix up mortar and attach the tile, you’ll be glad you took the time to find a concrete base, even if your design is just random tile.

Use Mortar Not Glue

The tiles should be attached with thinset mortar instead of glue. White PVA adhesives such as the Weldbond we sell are water resistant when fully cured, but there is a difference between water resistant and water proof. Flower pots are containers full of damp soil, and that means the back of the mosaic will be continually subjected to moisture and acids from decaying organic matter. The acidity of the leach water means that flower pots may be a more extreme environment for mosaics than pools and fountains.

Thinset mortar can also be used to grout your mosaic. Both grout and thinset are powdered portland cement products, but the thinset is stronger and more adhesive. If you are going to have to purchase a powdered cement product to make the mosaic, get the better product (thinset), and use it for everything. You can even reinforce the inside of a terracotta flower pot by plastering it with thinset.

Mosaic Stepping Stone Instructions

Mosaic stepping stones are great first projects, but they don’t have to be cheap and cheesy or dangerous. Keep in mind that if you totally cover the surface of the stone with large pieces of stained glass, it is likely to be slippery when wet. If you leave sharp edges of glass exposed, or allow the grout to erode out from between the glass over time, then your stepping stone is less of a stepping stone and more of a device for cutting bare feet. Both of these problems can be avoided by following best practices and using sound methods.

A Brief Rant

First, avoid the craft kits that have you make a butterfly or some other canned 1970s design by gluing large pieces of pre-cut stained glass onto a stepping stone. Glue will not resist moisture over time, and these kits are the poster child of slippery when wet. They also look exactly like all the other mass-produced stepping stones from China and thus have all the charm of a fast-food wrapper or billboard.

Instead, make something original by pressing your own designs of small tile into wet concrete, and be confident that whatever skill you lack may actually add to the originality and charm of what you make. A homemade stepping stone is supposed to look like a homemade stepping stone and not something made in a Chinese prison factory based on a design first copied in the 1970s.

Glass Tile Is Best

Glass tile doesn’t have any pores, and so water can’t penetrate into it and freeze and crack it. Ceramic materials have lots of pores, and there are tiny cracks in the glazing, so these materials are more susceptible to freeze damage. However, porcelain and dinnerware and other high-end ceramics are a lot more resistant to freeze damage than something like glazed bathroom tile, so they can be used with discretion. Remember, the more soft or crumbly a ceramic material is, the more susceptible it is to freeze damage. Avoid terracotta, glazed ceramic bathroom tile and anything that easily breaks.

Decide Which Method To Use

There are two main methods of making a mosaic stepping stone. It is better to use a mold if you are wanting to use marbles or large stones or other found objects not easily attached to a flat surface.

1. Prefabricated Stepping Stones.

You can cement tile to a plain prefabricated concrete stepping stone purchased from a lawn and garden center.

2. Stepping Stone Molds.

You can press tile into wet concrete in a stepping stone mold or have a mosaic design on contact paper at the bottom of a stepping stone mold and pour concrete on top of that.

Note that both methods require that you mix up a powdered concrete product because you cannot use glue to attach tile to an outdoor or wet mosaic. Instead, you have to use thinset mortar, which is a powdered portland cement with polymers added for enhanced adhesive properties and strength.

Prefabricated Stepping Stones

Plain concrete stepping stones can be purchased from lawn and garden centers. These make great bases for mosaic stepping stones even if you are wanting to press tile into wet concrete instead of cementing the tile to a rigid surface and then grouting later. How is this possible? Easy. You simply spread the mortar on a little thicker than normal, say about 3/8 inch thick, and press the tile into that.

Stepping Stone Molds

Stepping stone molds can be purchased or improvised from ordinary containers such as plastic dish pans and old metal cake pans from the thrift store. Various websites recommend using the nonstick baking pans from your kitchen and even make the claim that you won’t scratch them up, but I wouldn’t go that route. As a general rule, I avoid using anything from my kitchen in my art studio and then returning it to the kitchen, and I’m fairly sure that some people would manage to scratch the pan when they removed the hardened concrete stone. Besides, you can always get old cake pans from the thrift store or use a plastic dish pan or take an old plastic 5-gallon bucket and cut it down with a jigsaw. There is no reason to raid the kitchen when all these other options are available.

Tip: No matter which type of mold you use, make sure you coat it with non-stick cooking spray or petroleum jelly (Vaseline) to ensure that the hardened concrete stone can be removed easily.Sources of Improvised Molds:

mosaic stepping stone instructions

A stepping stone mold with some accessories. The pea gravel can be mixed with the thinset mortar to give it strength and bulk.

Sources of Improvised Molds:

  • plastic dish pans
  • plastic totes
  • purchased stepping stone molds
  • old cake pans from thrift stores
  • 5-gallon plastic buckets cut down with jigsaw
  • plastic litter boxes (new or bleached)
  • plastic plant trays
  • cardboard boxes lined with plastic trash bags
  • your spouse’s nonstick baking pans (not recommended)

Two Ways To Use A Stepping Stone Mold

There are two ways to use a stepping stone mold. You need to decide which you will use, and the second is better for marbles and other found objects that aren’t flat like ordinary tile:

1. Put the tile at the bottom of the mold and pour concrete over that.

You can place your tile UPSIDE DOWN in the bottom of the mold and pour the concrete on top of that. The easiest way to keep your tile from moving around when the concrete is poured on top is to put contact paper at the bottom of the mold with the sticky side up. Then you stick your tile UPSIDE DOWN onto the contact paper. This method is recommended if you want a very detailed design because it allows you to get all your tile carefully positioned before you mix up the concrete, which only has a few hours of working life before it starts to harden. Even if your design isn’t very complicated, I wouldn’t attempt it without the use of contact paper. Make sure you add the concrete slowly and gently tap the mold as you go along to make air bubbles come to the surface.

2. Press tile into wet concrete at the top of the mold.

This method is best for mixed-media designs made from marbles and other rounded found objects that couldn’t stick reliably to a piece of contact paper. You simply press the objects into the concrete, and you have the advantage of being able to vary how far they are embedded and to see how the work looks as you go along.

Tip: Wait 30 to 45 minutes before you start pressing objects into the wet concrete. This allows the concrete to firm up a little so that your objects don’t sink to far into it.

Using Thinset Mortar Instead of Ordinary Concrete

Thinset mortar mixed with a little pea gravel is MUCH stronger than ordinary concrete.

Most stepping stone instructions say to use ordinary concrete and often have tips about how to pick or sieve the larger pieces of gravel out of the concrete so that they don’t interfere with the tile or objects you want to embed in the concrete. One of the most significant hazards of doing mosaic work is breathing concrete dust, so if you were going to do this sieving or picking, you would want to do it AFTER you had mixed the concrete up, and that seems like a lot of pointless and difficult work to me.

Instead, I buy thinset mortar, which does not contain gravel, and I mix in small pea gravel in a ratio of 2 parts wet thinset to 1 part pea gravel by weight. For example, to make two small stepping stones, I recently used 8 pounds of wet thinset mixed with 4 pounds of pea gravel.

The pea gravel is needed because thinset mortar slightly contracts as it cures (due to the adhesive polymers), and all traditional portland cement products need and aggregate such as gravel or pea gravel to provide tensile strength.

IMPORTANT TIP: Set some of your thinset aside and don’t mix any pea gravel into it. Use this gravel-free thinset for the layer where your tile will be embedded so that no gravel interferes with the tile as you press it in. First, fill your mold about 3/8 inch from the top with the thinset mixed with pea gravel. Then fill the rest of the way up with the plain thinset. That top layer is where you would press the tile without having to worry about pea gravel in the way. If you have a pattern on contact paper at the bottom of the mold, you would first pour in some plain thinset and then top the mold off with the mixture of thinset and pea gravel.

Tips for Using Thinset Mortar

I have written some instructions for using thinset mortar and some tips for keeping your hands and tools clean while working with thinset mortar.

My instructions in those two links are for doing very detailed work with thinset. Most mosaic projects (such as stepping stones) are a lot more simple. Most of what you really need to know about thinset can be summarized here:

  1. Wear a dust mask when mixing up thinset to avoid breathing dust, and mix it up outdoors for easy clean up.
  2. For Versabond brand thinset, we mix 1/4 pound of water per 1 pound of thinset. The package will have manufacturer instructions for how much water to mix in.
  3. You have about 2 to 3 hours of working time provided you keep the thinset covered when not in use. If you are working in conditions of extremely dry air, such as when the heater or AC is running), then use a humidifier to keep the air moist.
  4. Do not dispose of thinset in plumbing or drains. It is concrete and can harden underwater.

Cleaning and Sealing

No matter which method you use, you should wait at least 24 hours before removing your stepping stone from the mold.

Sometimes stepping stones made on contact paper at the bottom of a mold will be removed from the mold, and the artist will discover voids between the tiles due to bubbles. Other times, you will see that concrete has gotten between the tile and the contact paper, and so there is concrete on top of the tiles. Both of these problems are easily fixed.

Voids are filled by mixing up small amounts of concrete and dabbing them in. Concrete on top of tiles can be scraped off using a small screwdriver or other steel tool. Use a spray bottle to mist the stone as you work to control any dust.

A few days after your stepping stone has hardened, you should seal it with a tile and grout sealer from a building material store.

Mosaic Backsplash Instructions

There is ample information online about how to go get sheets of tile from a building material store and mount them over your sink and grout them, which is merely basic tiling. This article is more about how to make an original mosaic design and about some basic questions not covered in most of the instructions I saw online.

How-To Questions

Can I tile over drywall?

Yes, for a sink backsplash. For showers and bathtubs, you should replace the drywall with concrete backer board because eventually someone is going to lean against it, and drywall won’t hold the weight. If the drywall has been painted, you will want to sand off the paint or at least scuff it with some coarse-grit sandpaper, something like 80 grit sandpaper.

Do I need to remove linoleum or formica or old tiling first?

Yes, adhesives and thinset aren’t likely to bond to materials designed to be stain resistant, and you don’t want the extra weight and thickness of the old material underneath.

The thickness of the mosaic tile means that my electrical receptacles will be recessed into the wall so far that the covers can’t be attached. How do I fix that?

You would use an electrical box extender (sometimes called and electrical box extension ring). These are available from a building material store such as Lowes or Home Depot. Basically, your electrician removes the receptacle cover, removes the screws that hold the outlets in the electrical box, installs the extender, and then screws the outlets to the extender and replaces the cover. As always, make sure the circuit breaker is turned off and test the outlet to confirm that it is dead before doing the work.

The process is simple and only takes a few minutes, but an electrician can ensure that you don’t accidentally do something that might cause a short over time (such as loosen a wire nut inside the electrical box). I’m a big believer in learning by doing, but electricity can be fairly unforgiving…

Do I need to use thinset?

Unless you are talking about a commercial sink or some other situation where the bottom of the mosaic is frequently standing in water, the answer is no. A high-end brand of white PVA adhesive such as the Weldbond we sell should be more than sufficient if the grout is properly sealed with a tile and grout sealer, which you need to do anyway to prevent staining and mildew.

Of couse, I am talking about attaching small mosaic tile (1″ or less) in an original design, which can be attached one tile at a time directly to the wall, or laid up on fiberglass mesh or temporarily reverse mounted on mosaic mounting paper. Note that our product descriptions for each of these include instructions for how to use them.

If you are mounting sheets or tile from a factory, or sheets that you laid up yourself, then you can spread thinset mortar with a 3/16″ notched trowel and press your sheets into that.

Do I Use Sanded Or Unsanded Grout?

Most of the instructional material I see online says to use unsanded grout to avoid scratching the glass tile, and then other websites say to use the new urethane grouts (which I believe only come with sand) because these are more resistant to mold and don’t have to be sealed.

I’ve never noticed a problem with sanded grout scratching tile, but I don’t use the new popular cheap tiles which are clear glass with enamel color fired on the bottoms. I suppose sanded grout might scratch these because the clear glass is relatively soft and shows scratching more.

Here is what I do know: I regularly get emails from panicky people saying that there are cracks forming in their grout lines as if the grout shrank as it cured, and these people all used unsanded grout. Unless your grout lines are very narrow, the grout needs sand to give it hardness and resistance to impact. Sand in grout is like the gravel in concrete: it isn’t optional if you expect the material to have any strength.

Of course, I am talking about traditional grouts made from portland cement because that is all I use. Maybe the newer epoxy grouts and urethane grouts don’t need sand, but I am unfamiliar. I do know that the working times of epoxy grouts are very short and clean up is more difficult, so you would only use them in situations where you are using ordinary flat tile that could be grouted quickly.

Do I need to seal my mosaic backsplash?

Yes, backsplashes definitely need to be sealed with a tile and grout sealer because they are subjected to occasional splashes, and not just water. There are also food and soap and grease and other materials likely to stain the grout and make it more susceptible to mold and mildew. We use ordinary tile and grout sealers from the building material store. Use multiple applications per the instructions on the bottle a few days after the grout cures. It isn’t complicated or messy. It wipes on and wipes off, and the only thing it does is seal the pores with silicone.

An Inspiring Mosaic Backsplash

Recently artist Karen Whitney emailed me pictures of her bathroom backsplash, which makes use of seashells and other dimensional found objects instead of ordinary flat tile and has a flowing curved border instead of a rectangular stopping point such as a ceiling or cabinet.


Artist Karen Whitney’s bathroom backsplash makes use of a flowing curve border that leaves most of the plaster wall untiled.

What I like most about this mosaic is the story Karen told me about making it, which involved trial and error, improvised methods and patience. This was how I started making mosaics (and most of the other media I have worked in): minimal information, just the basics really, and a willingness to experiment and see what works.

My first mosaic was made with a claw hammer without even the benefit of a tile nipper. That is how deeply my impulse to create had emerged: I had two engineering degrees and had grown up using all sorts of tools on all sorts of home improvement projects, but when my art finally took full control of my life, it did so explosively, and I worked almost by sheer will alone.

I won’t elaborate on the specifics of Karen’s materials and methods because things have a way of getting repeated out of context on the Internet and being cited as authoritative when they are not. Instead, I want to explain how to make such a mosaic using best practices, which ensure durability and can take a lot of stress and labor out of the process.

mosaic backsplash sink detail

The flowing border of Karen Whitney’s mosaic backsplash works well visually because the color of her grout matches the color of her plaster wall. All that being said, a completely contrasting color might have worked well, but I doubt if an in-between color would have. Note how the artist stopped the mosaic at the edges of her electrical covers.

Use Thinset Instead Of Grout

People often email me asking if they can press objects directly into grout instead of using the glue-then-grout method. Yes you could, in a way similar to how tile and objects are pressed into concrete to make a stepping stone, but it makes sense to use thinset mortar instead of grout for several reasons:

  • Thinset is a powdered cement product that looks and handles more or less just like grout.
  • Thinset has strong adhesive properties while grout does not.
  • Thinset is much harder and stronger than grout.

There is one important reason you may prefer to use grout instead of thinset: color. Most building material stores carry 30+ colors of grout but only 2 colors of thinset (gray and white). While thinset can be dyed, it is easier to find a grout that is already the color you want, and then you just add some latex additive to the grout to give it adhesive properties. The latex additive is sold on the same aisle that has concrete, and the package will have manufacturer instructions for how much additive to add to concrete (which would be the same for grout). Keep in mind that when you do this, you are essentially turning the grout into homemade thinset.

Seal Faces Before Use

Grout, thinset and other concrete products can stain any porous materials such as sea shells and unpolished stone. To avoid staining by grout, you can seal these items with a tile and grout sealer, which should be applied to the faces only using a small artist paint brush or a rag dampened with the sealer. Note that you will want to do multiple applications and take care not to get sealer on the bottoms of the objects or any place you want the grout to bond to.

This always seems like a lot of extra work to me, so I usually don’t do it, but that means I have to work extra careful when I mount my tile.

Note that Whitney used polyurethane on her sea shells, which might actually be preferable to a tile and grout sealer, which only seals the pores. The polyurethane is an actual coating, and this might do a better job of filling up tiny crevices where mildew and stains could lodge over time. I am unfamiliar with using polyurethane in this way and generally discourage its use on mosaic art because it might yellow or scratch over time. For seashells used in a shower, it might be a necessary risk to take.

Press Into Thinset Instead Of Glue-Then-Grout

Most mosaic is done like ordinary architectural tiling: tiles are mounted with adhesive or thinset, and then the mosaic is grouted by rubbing wet grout over the face of the mosaic and down into the gaps between the tiles. That is fine for ordinary flat tile, but the glue-then-grout method really doesn’t work when you have dimensional objects such as seashells. Of course it can be done that way in theory, but it takes a lot of rubbing to get the excess grout off something like that, and then there is the issue of staining.

That is why I spread a little bit of thinset mortar at a time using a small trowel or palette knife and press my dimensional objects into the bed of thinset. I don’t come back later and grout. Instead, I apply just enough thinset so that some squeezes up between my objects and fills the gap. It requires some trial and error to learn just how much thinset to apply so that an excessive amount doesn’t squeeze up and stain my objects, and that is why you might want to practice mounting a few objects to a small piece of scrap plywood before beginning your project.

I originally used a Wilton brand cake icing bag to fill in any voids a day or two later. Now I just mount the nipple from the cake icing bag onto a grouting bag because it holds much more material. An artists palette knife is also useful for this type of detail work.

mosaic backsplash tub detail

Whitney’s curving lines of glass gems suggest waves, which adds to the marine theme of the mosaic. Notice how the green gems contrast the warm orange of the shell used as a centerpiece.

Fiberglass Mesh

Whitney laid up her mosaic on fiberglass mesh so that she could work at her table instead of squatting in the bathtub to individually attach each shell. A PVA adhesive such as the Weldbond we sell is best for attaching tile and found objects to mesh. To attach mesh-mounted sheets to the wall, spread mortar using a 3/16-inch notched trowel and press the sheets into it. After the mortar has hardened over night, the mosaic can then be grouted in the conventional way (if using flat tile).

For a found-object mosaic such as Whitney’s, carefully apply small amounts of mortar between the found objects using a palette knife or grouting bag (instead of rubbing grout across the mosaic indiscriminately). This type of detailed concrete work is a labor of love and takes some time, but it is actually enjoyable because you can see the finished product emerging as you work. It is like putting the finishing strokes on a painting.

Mosaic Concrete Lawn Sculptures

There are two options for bases for making a mosaic sculpture for your lawn:

  1. Buy an unfinished concrete sculpture from a lawn and garden center or a store that specializes in concrete lawn sculpture.
  2. Make your own concrete sculpture using cement and chicken wire and pea gravel and similar reinforcing materials as discussed on various websites found by searching Google for “concrete sculpture” or our page for how to make concrete mosaic sculptures.

Note that my page focuses on a large structural base I was making at the time while some of the other websites have better pictures of how to crumple up chicken wire to make smaller figurines. However, the Internet contains a lot of problematic advice about hypertufa and other practices, so make sure you read my caveats below.

Each of these options has advantages and pitfalls that are important to consider before deciding which route you will go. Either way, following best practices to prevent moisture penetration is critical for ensuring the longevity of your mosaic lawn art.

Frog mosaic lawn sculpture

Frog mosaic lawn sculpture by artist Lyn Richards is an excellent example of how you can take a mass-produced concrete base and make it your own unique piece of art by how you tile it. Note how the artist used multiple green hues instead of one monolithic color field and how the greens contrast the reds and yellows, which are arranged in patterns that suggest motion.

Purchasing A Factory-Made Base

A factory-made base purchased from a lawn and garden center will be identical to all the other pieces made from the same mold, but there is obvious the advantage that you can start mosaicing immediately without having to make the base yourself, which is a complete project in itself and tends to be more labor intensive than expected, unless the artist has worked with concrete before. Also, you can make the generic base into an original work of art by how you tile it, as demonstrated by the artwork by Lyn Richards featured on this page.

Sealants Can Interfere With Bonding

If a drop of water soaks into the surface of the concrete, there is no excess sealant present, and the thinset mortar used to attach tiles should be able to bond securely.

Sometimes you can find factory-made sculptures that have been drenched in sealants, and these can interfere with thinset’s ability to bond to the concrete securely, and tiles could fall off over time. If a drop of water beads on the surface of the sculpture (similar to how water beads on a waxed car), then you know the sculpture is coated in a sealant that should be removed before mosaicing. To remove the sealant, scour the surface with a stiff wire brush of the type used to clean welds (the wires are stiffer and more coarse than those on most wire brushes used to clean barbeque grills).

Butterfly mosaic planter

Butterfly mosaic planter by artist Lyn Richards was made on a concrete base, which are much more durable than terracotta planters. Note how the artist used the grout line to add even more detail to the butterfly’s wing. Also note how the black grout makes the colors look even brighter.

Beware Of Lightweight Concrete

Sometimes factories will mix expanded perlite or other materials into the concrete to make it weigh less than regular concrete. This is fine in theory, but the expanded perlite is highly porous and mostly air and therefore readily absorbs water. This makes the sculpture highly vulnerable to freeze damage: water seeps in, freezes and expands, and then the surface of the concrete flakes off. If you find a sculpture that appears to be lighter than expected or has a softer or more porous look to it, then coat it all over (bottom included) with a layer of thinset mortar and allow that to harden before you mosaic on it.

mosaic bird bath

Birdbath mosaic by artist Lyn Richards. Outdoor mosaics on horizontal surfaces tend to have shorter lives as standing water penetrates between the tiles. Mosaic benches and birdbaths and other horizontal surfaces should be sealed with multiple applications of a tile and grout sealer to prevent this from happening. You should also consider cleaning and sealing these surfaces every year or two.

Making Your Own Concrete Sculpture For A Base

Mixing up even 5 pounds of concrete can be labor intensive, and mosaic lawn sculptures of any size at all can require 25 to 50 pounds at least. As you might recall from mixing up grout, your arms feel it even with the small batches, and most people will find a drill with mixing paddle necessary to mix up anything over 10 pounds.

Several of the websites explaining how to make concrete sculpture emphasize the need to make the bases hollow or to use Styrofoam or harder varieties of expanded polystyrene to fill internal voids. This is good sound advice, especially if you make the surrounding shell of concrete structurally sound by reinforcing it with metal rods and wire.

Thinset Instead Of Regular Concrete

There are different concrete mixtures recommended on the various websites, some of which include glass fibers used to give the concrete the tensile strength it normally lacks. For my concrete sculptures, I used thinset mortar instead of regular concrete. Thinset mortar is like regular cement with sand, but it also has polymers for adhesion and tensile strength. I also mixed in fine pea gravel for additional strength and bulk. The pea gravel was sieved to remove larger pieces and added 1 part pea gravel to 2 parts thinset on a weight basis.

Thinset is more expensive than regular concrete, but it is so much stronger, and you don’t have to worry about whether or not it is adhering well to a bare wire frame. Also, if you have to add concrete to a large frame in multiple batches mixed in multiple studio sessions, you can be confident that the fresh thinset is adhering to the thinset that is already hard, and you can’t say that about regular concrete, which is likely to form a crack at the boundary.

Of course, the concrete sculpture recipes I saw on various websites recommended different latex additives that should be added to the regular concrete to make it be more like thinset. But my thoughts were why reinvent thinset from different components if I could simply buy thinset, which was actually cheaper by the time you factor in the additives. Also, instead of picking or sieving the larger rocks from a bag of concrete, I thought it made more sense to start with a bag of thinset (which contains no stones) and add the exact size of pea gravel I needed to ensure it fit into my wire mesh frame.


Hypertufa is synthetic version of a type of porous limestone called tufa, and it is popular for making custom planters because its porosity is good for plant roots and getting covered with moss and lichens. Hypertufa is made by mixing peat moss and perlite and sometimes other materials into concrete to make it porous and lightweight.

About half the post you see on gardening blogs repeat the mantra the hypertufa is completely freeze proof. The other half are asking for advice of how to prevent their hypertufa planters from mysteriously cracking (usually with an acknowledgment that they accept the official dogma that the cracking couldn’t possibly be due to freezing temperatures).

What I do know is that all other porous materials I have encountered in my experience with outdoor mosaics are highly susceptible to freeze damage: terracotta, unglazed ceramic, unpolished stone, etc. If it has small holes in it, even tiny microscopic holes, then moisture penetrates and freezes and cracks or flakes the surface.

I’m not sure why hypertufa would be any different. The peat moss and perlite are ready conduits for deep moisture penetration. I strongly suspect that hypertufa is so soft that the damage due to freezing and expanding doesn’t result in macro cracks right away, and thus people with weak reasoning skills assume it is freeze proof. Later when cumulative damage finally results in a crack, the crack is attributed to the anger of the hypertufa gods or something like that.

Fish mosaic planter

Fish mosaic planter by artist Lyn Richards makes excellent use of glass gems as bubbles. Notice the mixed use of green hues in the seaweed and how the fish and weed are integrated and how they make use of contrasting colors from opposite sides of the color wheel (green and orange). The white makes these colors “pop” even more, as does the black grout.

I strongly suspect that hypertufa is so soft that the damage due to freezing and expanding doesn’t result in macro cracks right away, and thus people with weak reasoning skills assume it is freeze proof. Later when cumulative damage finally results in a crack, the crack is attributed to the anger of the hypertufa gods or something like that. “I must have done something wrong in how I mixed up the hypertufa or cured it. It couldn’t be the freezing winter conditions.”

All that being said, hypertufa is fine for someone making a simple un-mosaiced planter and wants it to crumble away slowly like natural limestone. But if you are going to the time and expense of covering it with mosaic tile, then avoid hypertufa. If you want to make a lighter core from concrete mixed with perlite, that is fine, but cover the outside with a layer of thinset before you mosaic to ensure that the vulnerable porous material is protected from the risk of moisture penetration and freeze damage.

How To Mosaic A Concrete Lawn Sculpture

Like all outdoor mosaic and wet mosaic, the tile should be attached with thinset mortar instead of glue. Other than that, the instructions are more or less the same as our instructions for regular flat panel mosaics. I wrote some detailed instructions for using thinset mortar for mosaic art.

You can grout an outdoor mosaic with thinset instead of grout. Thinset is harder and more water-resistant than traditional grout, so it is probably better to use thinset for grouting. Thinset can be dyed with concrete dye. (Note that I am always talking about traditional powered thinset mixed with water and NOT the new epoxy-based systems with a liquid component). I use Versabond thinset in my work, and I have exceeded the dye manufacturer’s maximum recommended amount of dye in the thinset by a factor of 2 without affecting hardness or bond strength in any way that I could notice, but I am sure that it is possible to add too much dye depending on the brand.

Tip: Put cardboard on your work table to protect it from the weight and roughness of the concrete sculpture.

Tip: Rest the bottom of the sculpture on small blocks such as stone tiles or whatever so that you can mosaic and grout the bottom edge of the sculpture without the surface of the table getting in the way.

Tip: Consider sitting your sculpture on some plain concrete stepping stones when you install it in the garden by raising it slightly off the moist soil, you can greatly increase the life of the mosaic, especially the tiles near the bottom edge.

Tip: Use a pencil or marker to draw patterns on the surface of the sculpture.

Tip: Never use one color blue to make a color field when you could mix two similar blue colors to make the same field of color. It makes the element more visually interesting.

REQUIRED: After your grout has hardened for a few days, seal your finished mosaic sculpture with multiple applications of a tile and grout sealer following the instructions on the package. It wipes right off glass tile and only seals invisible pores.

Thinset On Plywood Mosaic Backer?

Thinset mortar can be used on a plywood mosaic backer provided the plywood has been sealed with a white PVA adhesive such as Weldbond. Otherwise, the plywood can suck the moisture out of the thinset before it has a chance to harden leaving it soft and crumbly. It is important to seal the plywood at least a day or two before you mount the mosaic with thinset because the Weldbond needs to be thoroughly dry and cured. For sealing purposes, Weldbond can be painted on with a brush or spread with a trowel. Many mosaic artists dilute the glue slightly or even up to 1:1 with water to make it easier to spread. Note that you shouldn’t seal your plywood with paint or sealers chosen at random because thinset will not bond to some of the oil-based and silicone-based products.

Some artists seal their plywood backers with Weldbond before mosaicing even if they are going to use that same Weldbond to mount the tiles. Why? They want to make sure that the entire surface of the plywood has been sealed so that it doesn’t suck the moisture out of the GROUT when it cures. I never worry about sealing the face of my plywood because I am sure that I will get enough Weldbond spread around when I mount my tile, and so pre-sealing seems like an unnecessary extra step to me.

Sealing VS Sealing

A note of clarification: In this article, I am talking about pre-sealing the face of the plywood with Weldbond or some other PVA adhesive. This is a different step from sealing the finished mosaic a few days after grouting with a tile and grout sealer or “sealing” the edges and back of the plywood with paint or varnish to prevent warping by moisture.

When You Should and Should NOT Use Plywood

Plywood can warp and delaminate over time merely from the humidity in the air, and so you should never use plywood as a backer for outdoor mosaic or a mosaic in a damp location. However, plywood makes a great backer for dry indoor mosaics and not just for its light weight, which in itself is a significant advantage over concrete backer board. Unlike concrete backer board, the edges of plywood can be stained or painted, and they do not shed crumbs of concrete and sand. In my opinion, concrete backer board should only be used inside walls and floors and other places where its crumbly edges are covered up; it is not a backer for moveable mosaic plaques.

Use Cabinet-Grade Plywood

Note that you should spend the extra money and buy cabinet-grade plywood (in 1/2 inch thickness) instead of the ordinary plywood used for sheathing in construction. The cabinet-grade stuff comes with a sanded finish and has no knots or internal voids. It is also more resistant to warping, and the edges of cut pieces are cleaner than those cut from regular plywood mainly due to the lack of voids in the internal plies. With all of these advantages, the cabinet-grade plywood is only about 15% to 25% more than regular plywood, and in real terms it is actually the same price: some of the regular plywood may need to be scrapped due to internal voids, and it will require more work to make the edges presentable. The edges of a cut piece of cabinet grade plywood can be left plain or painted. The edges of a cut piece of regular plywood will have voids and require putty, sanding and paint if not a frame to look presentable.

Why Use Thinset on Plywood?

If plywood can only be used for dry indoor mosaics, then why would someone need to use thinset mortar on a piece of plywood anyway? The simple answer is there isn’t any reason to do so (IF you are using regular flat tile). With flat glass tile, you simply glue the tile on with Weldbond or some other PVA adhesive, let it dry for a day or so and then grout it by rubbing wet grout into the gaps and wiping away the excess.

However, some people (including myself) like to use rounded and irregularly-shaped found objects in our mosaics, and these are not easily grouted. Instead of the glue-then-grout method, we like to press our objects into a bed of mortar so that the excess mortar presses up slightly around the object and skip grouting entirely. It is also necessary to avoid grouting if your found objects are naturally porous (seashells, bones, unpolished stones) because grout will stain these materials.

solstice-door mosaic detail

The face of “Solstice Door” mosaic stele was made from a lifetime’s collection of found artifacts embedded in thinset mortar. Note that the stele is a reinforced concrete monument. Plywood would not support the weight of these materials.