Tag Archives: concrete

Mosaic Bird Bath

Artist Lyn Richards sent me some pictures of the mosaic bird bath she made this past summer, and it is worth showing off. The floral design and the colors used in the mosaic were inspired by Van Gogh’s painting “Irises.”


Mosaic bird bath by artist Lyn Richards makes good use of contrasting colors and a Van-Gogh-inspired floral design that help integrate the bird bath with its surroundings. Note the use of an ordinary concrete stepping stone as a footing/base to keep the mosaic work separated from the soil. This is recommended because the acids in decaying organic matter slowly rot stone, concrete and grout.

Material List for a Mosaic Birdbath

Concrete Base

To make a mosaic bird bath such as this, you could use a ready-made concrete bird bath from a lawn and garden center, or you could make an original concrete sculpture if you are looking for something with a less conventional shape. Lyn used a ready-made concrete bird bath that came in two sections: a base column and a bowl.

Thinset Mortar and Tools

Thinset mortar should be used instead of adhesive for attaching the tile. A complete list of tools and materials for mixing thinset and for applying it is given in my instructions for using thinset mortar with glass tile. (Note the instructions were written for doing extremely detailed work, so I might make thinset seem much more difficult to use than it really is.) I have also written a page for how to keep your hands clean when using thinset.

 Glass Mosaic Tile

Glass mosaic tile in non-porous and so water can’t get inside it and freeze and crack it all to pieces. This makes glass superior to stone and ceramic tile when used outdoors. You can use any of the glass we sell. Lyn’s mosaic was made from different brands of 3/4 inch vitreous glass tile, metallic glass tile. iridescent glass, and stained glass.

To find out how much tile you need, you can divide your shape into component surfaces and use our mosaic tile estimator.  What do I mean by component surfaces? For estimation purposes, Lyn’s bath can be thought of as cylinder topped by a disk. The surface area of the cylinder is A = D*Pi*H, where D is the diameter, and Pi is 3.14, and H is the height. The surface area of the disk is A = Pi/4*D*D. Note that this time D is the diameter of the bowl and not the pedestal base. Remember to multiply the surface area of the disk by a factor of 2 because there is a top and a bottom.

As always, remember to inflate your estimate by 5 to 10% to account for cutting scrap and to provide a cushion for error in your estimates. I have always found that it is much better to have tile left over than it is to not have enough. Suppliers sell out from time to time, and the next manufacturer batch might not match what you already have, or at least match exactly. Also, leftover tile serves as inspiration and material for future projects.

Finding and Transferring Patterns

Lyn used Van Gogh’s painting “Irises” for her pattern. She drew the outline of the shapes (blades and petals) onto the concrete using a pencil, and then she went over that drawing with a black Sharpie marker when she was sure she had her lines correct. This is recommended: Don’t use the marker until I work out my lines by trial and error using a pencil. If your pencil drawing gets to be a mess and you need to start over, you can “erase” it by wet sanding it and wiping it off with a rag.


To create a sense of depth and shading, Lyn used multiple shades and hues of green for the leaves of the irises instead of one color.

Choice of Colors and Visual Interest

Note how Lyn used multiple shades and hues of green to make the blades of the iris leaves instead of using just one type of green. This creates shade and depth and visual interest and makes all the difference in the world. Monochromatic color fields are boring, and they take just as long to tile as a more interesting mix of colors. Note the solitary pea green blade of new growth and how it stands out from the other leaves, which are a mix of darker and bluer greens. Similarly, the petals of the irises are made from multiple cyan blues and ultramarine blues instead of one color, and this makes them more lifelike and more visually appealing.

Andamento and Visual Interest

The background of a mosaic is an opportunity to add visual interest to the scene and should never be “bricked” up like the tiled wall of a shower. Andamento is the visual flow of a mosaic created by arranging the tile in rows, and it can make the background of your mosaic as visually interesting as the figures in the foreground.


Lyn’s strong use of andamento creates a sense of motion in the background. When used to its full potential, andamento can make the background as interesting as any figure in the foreground, as demonstrated here.

Observe how Lyn used multiple related hues for the background instead of one color. Also note there is not a single whole tile mixed in with all these cut pieces. Why not? A uniform square would stick out like a sore thumb among all the irregular pieces.

Cutting and Attaching the Tiles

Thinset is concrete that hardens over time. I can usually get three hours out of a batch, and I often work in sections, usually completing about 1 or 2 square feet per session, depending on how detailed my work is. Lyn found it useful to have her tile cut up in advance of a session, but you can always make incidental cuts as needed while you are attaching tile. Again, my thinset instructions explain the details of how to handle and use the mortar to attach tiles. Tip: partially crushed liquor boxes make great cradles for holding heavy pieces of stone and concrete while you tile them.

Removing Sharp Edges

A marble file or a rubbing stone can by used before the tile is mounted to remove any sharp edges. After the tile is mounted, it is a little more difficult to remove sharp edges, but gently rubbing the surface of your mosaic with a rubbing stone can help a lot.


Before grouting, you should clean off any excess thinset from the face of the tiles. Scraping this off will also make any loose tiles fall off so that you can reattach them before grouting. You should wait a day or two before grouting to let the thinset harden. Black grout is best for making your colors stand out. Lyn used a combination of black, gray, and brown grouts, and she blended these to get the exact color she wanted. A few days after your grout hardens, you should buff all the grout haze off and seal the finished mosaic with multiple applications of a silicone-based tile and grout sealer, such as available at any building material store.


Lyn Richard’s mosaic bird bath at home in her garden.

Outdoor School Mosaics

Recently I received an email from an art teacher whose school mosaic project was an outdoor mosaic where each child would create a mosaic on an 8 inch x 8 inch brick paver (paving stone), and then the mosaic pavers would be arranged together in a crazy quilt design similar to what artist Victor Kobayashi created for his mosaic patio in Honolulu.

I really like the crazy quilt approach to school projects because it allows each student to make their own art and have a real art experience instead of copying some teacher’s favorite piece of art, which usually involves more boredom or frustration than it does art. Crazy quilt projects also tend to produce more exuberant and impressive results. Copying something is merely copying something, even if that something is an acknowledged masterpiece.

Normally, school mosaic projects can use 1/2-inch or 3/4-inch sanded plywood as a backer, and the tile can be attached using a white PVA adhesive such as Weldbond, but plywood and glue are for indoors only. For outdoor and wet mosaics, you must use thinset mortar to attach the tiles to the backer, and that backer must be cement, stone or masonry. For large mosaics, a sheet of concrete backer board can be mounted to a metal wall using a frame welded from angle iron, or the mosaic can be created directly on a stone or concrete wall or a brick wall plastered smooth with thinset. In this case, the mosaic can be laid up in advance on fiberglass mesh, mosaic paper or clear mounting tape, and then these sheets can be pressed into thinset spread on the wall using a notched trowel.

This particular teacher decided to use brick pavers for her backers, but the concrete stepping stones/pavers commonly sold at building material stores could have been used in a similar way. The real issue for her project was how the students could use thinset mortar to attach each individual tile without creating a huge mess.

Thinset mortar is a sanded portland cement product with polymers added for strength and adhesive properties, so think of it as sticky concrete because that is essentially what it is. Your students might be mature and competent enough to use a bottle of glue that looks and handles just like Elmer’s glue, but how are they going to fare when they start working with sticky concrete? Now that I have your attention and your hair is standing on end, let me calm you by saying that it can be done, and it can be done fairly easily with a little forethought and planning.

One option would be to avoid setting each tile individually and lay up the designs in advance on clear mounting tape using my instructions for using contact paper and mounting tape. Then thinset could be spread on the pavers and the whole design mounted at once.

But that still involves handling thinset and some point, and sometimes you find situations where the mounting tape method isn’t practical (such as when not all of your tile have the same thickness).

Make A Prototype To Answer Basic Questions

The key too minimizing frustration and mess is to figure out your process BEFORE you involve the children, and the best way of doing that is to make a prototype in advance. In making a small mosaic beforehand, you work out the details of your materials and methods, including how the thinset will be distributed between the different children and how they will apply it to the backer.

Here are some questions you should answer by making your prototype. Please don’t let any of these alarm you because I have a practical recommendation at the end of this article that greatly simplifies everything and even eliminates some of these concerns:

How long does it take to apply tile to a mosaic of this size?

How many classroom sessions will be required?

Would it be more practical to have longer sessions instead of a larger number of short sessions?

How will thinset be applied to the stepping stones? Will the children spread the thinset themselves?

How will the children keep their hands clean while working; buckets of water and piles of rags?

How will we keep the thinset from drying out in the heated winter air or summer AC? Can we use humidifiers if necessary?

How much thinset do you need to mix up at one time? (This is answered by thinking about how many students will be working at once and how much thinset you used in one working session.)

How will we mix up the thinset? Is a parent volunteer available with a mixing paddle, drill motor and 5 gallon bucket? Do we have any parents who work as contractors and have experience with laying tile or mixing up concrete?

All of these things are relatively easy to implement, but they can make things chaotic or difficult if you don’t think about them in advance.

Thinset And Surfaces

There are a few specific concerns related to using thinset and pavers/stepping stones.

Surface Wetting

Sometimes you can drop a clump of thinset onto concrete backer board and it will harden without bonding to the backer board and it will fall right off or come off with minimal scraping. This was because the thinset didn’t really make intimate contact with the board due to surface dust. This can become more of an issue over time as you work and the thinset starts to set up as you are using it. The point is that sometimes you need to smear thinset into a surface to make sure it adequately wets the surface and makes intimate contact. Normally this happens merely by pressing a tile into the thinset, but you might do well to keep an eye out for students who are minimalists in terms of how much thinset they apply and for those who have a butterfly touch and just kind of sit the tile on top of the thinset instead of pressing it in.

Presealed Pavers

One problem you might encounter is pavers or stepping stones that have been sealed with some sort of silicon or polymer that might interfere with thinset bonding well to them. You can test for this simply by dripping some water or spittle on the paver and observing whether or not the water wets the surface. If the water wets the surface and soaks in, then there shouldn’t be any problem. If the water beads up similar to how water beads on a waxed car, or if it fails to soak in, then you know that the pavers have a heavy coat of sealant and should be avoided.

Skin Irritation

Wet concrete is mildly caustic, so it can dry and irritate the skin. A box of disposable medical examination gloves from the drug store can prevent this. You should also have the children wear safety glasses with side shields.

Overly Complex Designs And A Recommendation

Another thing you can learn from making a prototype is how much time is involved and how simple or complex the designs can be in order to be completed in the time allowed. I definitely prefer children be allowed to make original designs so that they get a real art experience, but you still need to give them recommendations about what level of detail is practical and look out for children trying to make overly complex and detailed designs. For this reason, it can be somewhat problematic for children to sketch out their designs in advance. Sometimes the mere act of drawing gets a person thinking in terms of a level of detail that isn’t practical in the medium in which the design will be executed. I have encountered this time and again while sketching out designs for my painting and mosaic.

Instead of sketching out designs, a more practical exercise might be for the students to play around with arranging tile before they decide on a finished design and definitely before they work with concrete.

I recommend making cardboard squares the same size as the mosaic backer and allowing the children to practice laying up their design on the square. If possible, give them one session to play with different arrangements and experiment with rendering different designs in the square, and a second session to finalize their design.

Then the following sessions could be about transferring the tile to the thinset on the paver. Using this approach, it would be possible for a teacher or parent volunteer to spread thinset on the pavers, and then the students merely transfer their tile designs from the cardboard squares/trays to the thinset, which would greatly minimize the amount time the children spent touching concrete.

A Practical Method For Kids And Thinset

  1. Make squares from cardboard that are the same size as the stepping stones/pavers or draw squares the size of the pavers on cardboard or trays. I prefer to cut out the cardboard squares so that they can be wrapped with contact paper with the sticky side out to prevent the tile from moving around.
  2. Have children spend one or two sessions arranging tile into designs on these squares/trays.
  3. Have teachers or parent volunteers mix up and spread thinset on the stepping stones.
  4. The children transfer their designs to the stepping stone one tile at a time. Alternatively, clear mounting tape could be used to pick up and transfer more complex designs made from smaller tile.
  5. After the thinset has hardened for a day, grout the mosaics with more thinset or grout.
  6. After the grout has hardened for at least a day or two, clean off any remaining grout residue by rubbing with a clean cloth and seal the mosaics with a tile and grout sealer.


The above instructions were written for children and beginners who just need to play around with tile to make simple designs. However, you may have more advanced students capable of making more sophisticated images from many small pieces of tile. I have written a second article Mosaic Transfer Instructions which explains how to lay up a more complicated design on a pattern and transfer it all at once to thinset or cement using mosaic mounting tape or clear packing tape.

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 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.

How To Use Found Objects In Mosaic Art

Making and grouting a mosaic from ordinary flat tile is relatively straight forward. However, adding three-dimensional objects such as porcelain figurines or even simple rounded stones can complicate the grouting process. Instead of using a grout float or damp sponge to wipe away the excess grout, you may need to use a gloved hand as we often do, and you may have “excavate” some objects using brushes or dental picks if they have very complex shapes with nooks and crevices. An old toothbrush can be useful for cleaning wet grout from crevices in objects, but note that brushes of all type remove grout very aggressively, so take care that the toothbrush doesn’t gouge out any grout from where it needs to be.

If your mosaic is mostly dimensional objects, then the amount of labor required to remove excess wet grout may be excessive, and the easiest way to solve the problem is to avoid the grouting process entirely. Also, unsealed porous objects such as seashells cannot be grouted without staining them with the grout.

For these situations, it is better to press the objects into thinset mortar instead of the usual glue-the-grout method used for making indoor mosaics.

Thinset is a type of concrete, so if you spread it on slightly thicker, then a little bit will press up around the sides of the objects and serve as grout between the tesserae (“tile”). The key is to not spread so much thinset so that the object sinks in too deeply or too much thinset squeezes up and around the object.

Before you start pressing your childhood treasures and precious souvenirs into the sticky wet concrete that is thinset, you will want to practice for a few minutes with some ordinary rocks on piece of scrap. That way you can figure out how thickly to spread the thinset to avoid problems and practice keeping your hands clean while working with wet concrete. Otherwise your fingertips are likely to get wet concrete on objects that aren’t easily cleaned.

Your quick experiment on a piece of scrap should use more than one size of rock and include pressing objects close together. That way you can decide how closely you want to space your found objects in your actual mosaic and see how small objects have the potential to be buried in thinset pressed out by large objects nearby.

Keep in mind that small experiments like this do not require any extra time. Whatever time that is required to do them is almost always made up for in the time they save you on your project.