The Blue Crab mosaic I recently completed is a good example of how to create a grout gap by making use of imperfect cuts instead of spacing the tiles intentionally.
The “imperfect cut” method makes the process of creating a mosaic faster, easier, and less tedious -first in the cutting and placing of tiles but also in the grouting process.
That “error” will create the grout gap for you.
Tracy Kaplan recently emailed us a picture of her FIRST mosaic, and it is nice solid work, impressive even, especially considering that her instructor gave her some problematic advice concerning the grout color. Tracy’s teacher had recommended a chocolate or nutmeg colored grout, but Tracy wisely considered how a dark brown might cause adjacent tree trunks to no longer be distinct and separate.
Perhaps Tracy’s instructor had meant a lighter shade of those browns, but I still think that those could have caused problems with the adjacent tree trunks.
Most likely, the instructor only saw a portion of the mosaic without adjacent tree trunks. Tracy admits that she only finished about an eighth of the work during the course and spent many months afterward working to complete it.
If so, this is yet another example of how artistic advice isn’t one-size-fits-all and can be counterproductive or even disastrous if the advice isn’t specific to a particular artist or even a particular work of art in its entirety.
Fortunately, Tracy emailed us for advice.
Mosaicists sometimes mix in artist acrylic paint to create custom colors from white grout, but you can also use acrylic paint to “stain” grout after it has hardened (for dry indoor mosaics).
Like the process of staining wood, “staining” grout with paint is a process of wiping on and wiping off. The paint sticks to the rough grout but wipes off the glass tile.
In my recent blog article about black and white grout, I wrote the following tip for minimizing the width of grout gaps and working a little faster at the same time:
If tiles only touch at points but not along the length of their sides, then tiles can be positioned very closely and yet still be grouted. Consider working in this way instead of carefully cutting each tile to maintain a uniform grout gap.
I need to clarify what I meant by that.Uniform Versus Consistent
Sometimes novice mosaicists will carefully cut each tile to maintain a perfectly uniform gap, which can be a little tedious, and worse yet, they make the gap a little wider than it should be because the artist does not have the experience to visualize what it will look like when grouted.
I think it is better to work a little less uniform, and to err on the side of being slightly narrow, even if that means tiles occasionally touch at a point or corner. By better, I mean more efficient, less tedious, and better looking.
All that being said, it is extremely important that the mosaic have the same type of grout gap in all regions. You want to be consistent in your style of gap. You do not want to have loosely executed in one place and tightly uniform in another, nor do you want wide gaps in one region and narrow gaps in another.
Black grouts bring out the intensity of tile colors while white grouts overwhelm them. Natalie Knox’s Day of the Dead Skull mosaic is a good example of how well black grouts work and how a light colored backer isn’t a good indicator of the mosaic would look with white grout.Don’t Be Fooled
If you lay the mosaic out on a white backer and try to use that as an indication of what the mosaic will look like with white grout, remember this:
When the gaps are filled with grout, they won’t have all the contrast provided by empty gaps, which have depth and shadow. A lot of white concrete at the same level as the surface of the glass tends to make the colors look washed out.
Artist Sherri Grasmuck created a mosaic facade of Guatemalan women on her house in Philadelphia that is the perfect case study for choosing a grout color.
Choosing a grout color is more of a situation where you want to avoid making a mistake that causes the tile to look wrong than it is an opportunity to tie in the room’s color scheme by selecting some optimal color.A Case Study
Should you match grout color to a room’s color scheme? Not necessarily. Making sure the grout color works with the tile colors is much more important.
Recently a customer emailed us the photo above and asked for advice on how to match the grout color to the room’s color scheme, which includes rich gunstock brown cabinets and paint that is pale green or taupe and a black counter top. The mosaic backsplash itself is made from long gray and black tile in varying lengths.Choosing By A Process of Elimination
Grout colors should always contrast tile colors enough so that each tile is visually distinct. If you were to use a gray grout on this mosaic, the gray tiles wouldn’t stand out as individual tiles. If you used black grout, you would would have the same problem with the black tiles. Since the mosaic is a gray and black color element, a white grout of some shade makes sense. A pure white grout is likely to be too bright, and so an off-white grout that is more or less the same color as the exposed backer between the tiles would be a safe choice.Too Clever for Your Own Good?
What if you still thought that you needed to tie in the grout color to the room’s color scheme? Then you might consider using some sort of terracotta or brown grout in either a light or dark shade. The problem with that approach is that there are many different hues of gray, and not all of these will look good with a particular brown, even if that brown is optimal for the room.
If you are bent on using some sort of brown or other color for a black-white-gray backsplash such as this, then make sure you take some of the tile with you to the building material store and actually hold the tile up to the grout swatch. That way you can see if the hues look odd together. Avoiding that mistake is much more important than trying to match the other colors in the room.How You Know This Is Good Advice
Notice how the counter top is black, and the stove and microwave oven are black and silver in color. They don’t have any brown or taupe color elements, but they are perfectly at home in the room’s color scheme. Similarly, the mosaic backspash is a black-white-gray color element that needs nothing extra to tie it in.
Black and White Telescope Mosaic. Mark’s grandson gazes at the stars.Stylized or Photorealistic?
Mosaic is usually used to make stylized images, meaning images that are simplified in certain ways, and that is done because the constraints of working with tile that only comes in certain colors and can only be cut so small forces the artist to simplify the details. Think about how ancient Roman mosaic faces and figures are outlined like cartoons and how scenes are composed of 6 to 8 colors, and you will know what I mean. I strongly prefer this type of art because it is a dialog between the symbolic and visual aspects of the artist’s mind, and it produces a lot of quirky and interesting details that would never be possible in mere realism.
BUT, it is important to remember that you can use mosaic to render images in a naturalistic or photorealistic way even if you can’t find tile in all the colors you think you need. First, you can use two colors in place of one. For example, if the teal color you think you need is not available, use small pieces of blue and green tile positioned closely together and rely on the eye blending the two colors together.
Another means of working photorealistically is to make a monochomatic mosaic or a black and white mosaic, such as Mark did using our 8mm recycled glass mosaic tile when he made the mosaic of his grandson peering through a telescope.
Note that Mark’s mosaic doesn’t use concentric rows of tiles to convey a sense of motion such as seen in the andamento of most stylized mosaics. Rather, the tiles are treated as pixels in a grid, which is how most though not all photorealistic mosaics are made. The alternative to gridded pixels is to use large irregularly-shaped pieces in a mode similar to stained glass artwork.Patterns For Mosaics Made From Photos
I didn’t ask Mark how he made the pattern for his mosaic, but I know how I would do it:
I would take the photograph I wanted to use and convert it to a black and white image using Photoshop or another photo-editing software package.
Then I would enlarge it to the actual size I needed and print it out in sections, and then tape these together on my work table.
Then I would would cover this pattern with clear contact paper, WITH THE STICKY SIDE STICKING UP.
Then it just a matter of positioning tiles over the pattern and filling in the design.
The only question is: Do I put the tile right side up or upside down?Upside-Down Tile
If the mosaic is relatively small. I can spread adhesive on the backer and then press the backer onto the mosaic. In that case, I would want to position the tile upside down. Of course, this reverses the mosaic design from left to right as if in a mirror. Complete instructions for working in this way are given in my blog article Using Contact Paper To Transfer A Mosaic Design.
TIP: If you don’t want the above method to reverse your design from left to right, then reverse your pattern from left to right in the photo-editing software that you use to make the pattern.Right-Side-Up Tile
If I would like to work with my tile right side up so that the mosaic is not reversed, then I can use clear mounting tape or opaque mounting paper to pick the mosaic off the contact paper and then press it onto an adhesive-covered backer. This method is commonly used for laying up large mosaics such as murals. Instructions for this method are given in my blog article Mounting A Mosaic On Clear Adhesive Film.To Grout Or Not To Grout?
Grouting can totally change the look and feel of a mosaic, and so this question can be critical for photorealistic work depending on the colors and grout gap used. You can minimize the visual impact of grout by making sure that your grout gap isn’t too large. For most mosaic tile, the recommended grout gap is 1/16 inch, but for 8mm and 10mm tiles, use a grout gap of 1/32 inch.
For dry indoor mosaic, you can mount the tiles so closely together that they touch and simply not grout the finished mosaic.
You should also test grout colors before you apply them to the mosaic. The “test” can be as simple as taking some of your tile to the building material store and holding them next to different color swatches in the grout aisle.
For his mosaic, Mark did exactly what I recommend: he glued some of his tile to a scrap piece of plywood and grouted them with different grout colors to see what they looked like in situ.
The visual impact of grout color on a mosaic can be evaluated by gluing some tile on a scrap piece of backer and grouting it.
If that seems like a lot of extra work, the simple truth is that it isn’t. An experiment like that can be done in 15 minutes of gluing one night and 15 minutes of grouting the next, and what is that compared to the amount of time spent on the mosaic itself? Before you dump concrete on something you spent a month creating, make sure you are using the right color concrete.
Grout does not shrink, but it is prone to forming voids and bubbles if it is not rubbed thoroughly into the grout gaps. These holes are easily repaired.
My friend Fredrik reported a problem while grouting his mosaic portraits of famous rock icons. He described the grout as having shrank in the grout gap.
The grout didn’t actually shrink, which isn’t possible with traditional grout made from portland cement, sand, and water. (I can’t speak for the newer epoxy-based grouts because we haven’t used them.) What actually happened was that voids were left in the intersections of the groutlines, and these voids got covered with a thin film of grout that then dried out without curing.Press Grout DOWN Into The Gaps
When you grout a mosaic, it is important to press the grout down between the tiles, and to rub and press the grout thoroughly. Otherwise, voids and bubbles will be left down in the gaps and get covered over with a superficial layer grout similar to how a thin layer of wind-driven snow and ice will sometimes form over a crevasse in a glacier. That is why pressing down is important, and you shouldn’t just rub tangentially across the surface.
You can also “pull” voids into grout by rubbing it repeatedly in the same direction. That is why it is best to rub in circles and to vary the direction of the rubbing randomly.Avoid Dry Air: Use Humidifiers
Fredrik reported that he wasn’t able to able to spend very long pressing the grout into the gaps because it started to harden almost immediately. It takes grout a while to harden, and this hardening happens by binding water not by drying out, but grout can become prematurely stiff and difficult to manipulate if it starts drying out. Since Fredrik was working in Sweden in February, I suspect the air was very dry due to the heat running, not to mention the already low humidity of the winter air. You can avoid this problem by running a humidifier near your mosaic and by doing the grouting away from heater vents. You can also cover the grouted mosaic with plastic kitchen wrap such as the Saranwrap brand.How To Fix Holes In A Groutline
The good news is that it is possible to grout voids and holes and bubbles in a mosaic that is already grouted. The only caveat is that the old grout can suck the moisture out of the new grout before it can properly cure and harden. To prevent this, mist the mosaic thoroughly with water before you begin so that the old grout is saturated with water. Note that the mosaic should not be coated with water because droplets of water or a thin layer of water could interfere with intimate bonding. It really helps to have a humidifier running near the mosaic, and you should start the humidifier an hour or so before you grout so that the old grout isn’t bone dry.
Before you regrout, you need to expose all the hidden voids and bubbles. You can do this by pressing on the grout with a small screwdriver and vacuuming out all the loose crumbles. Of course, you need to do this in places that look like there is a problem, and but you also need to press in places that look deceptively fine. You don’t want to have to grout a third time.
I prefer to press straight down instead of dragging the screwdriver because I want to avoid scratching up grout that is fine. If you do get some scratched up grout from your probing, use a stiff bristle brush and a little water on the finished mosaic to buff out the scratches and make them less noticeable.
If you notice that your grout is crumbly in general, you should scrape it all out and regrout. In that case, you might want to use the grout removal tool.Mixing Up Small Amounts of Grout
One objection to fixing small grout problems is that people don’t want to mix up a whole container of grout and end up wasting almost all of it. The good news is that you don’t have to waste any or at least very much, and you don’t have to be paranoid about whether or not you are adding the right amount of water. You can easily mix up a small amount using a few rules of thumb:If you have a small postal or kitchen scale, use 1 part water by weight to every 4 parts dry grout. If you don’t have a small scale, add a little water and mix thoroughly. Stop adding water when the grout has the consistency of dough. Once you have enough water in the grout, mix it thoroughly to ensure even consistency with no tiny lumps of dry material. These can sabotage the grout hardening process.
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 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
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 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.
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.
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.
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.
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.
The primary reason for grouting tiled surfaces is to prevent water from penetrating behind the tile and weakening the adhesive or the backer and the structure beneath the backer. In mosaic artwork, the grout also has a visual function, and that is to contrast (not match) the tile colors. If the grout color does not sufficiently contrast the tile colors, than all the tiles blend together visually, and much of the “mosaic effect” is lost.Grout Color Should Contrast Not Match
There are some novices who doubt my advice about contrasting grout color and even try to match their grout color to the tile colors. These are the people who later email me in a complete panic. They usually use the words “completely ruined” to describe what grouting did to their once beautiful mosaic, and from the pictures they send, I’m inclined to agree with them. (Note that these mosaics can be saved, but it requires either scraping the grout out with a grout removal tool or painting the grout with acrylic paint or some other ad hoc solution.)A Medium Gray Grout
Since experience has shown time and again that the best grout color is one that contrasts tile color, the question becomes which grout color best contrasts ALL the different colors used in the mosaic. For MOST combinations of tile colors, the best contrast is usually provided by a medium to dark gray, with darker being the better guess if in doubt. Always keep in mind that the color of the grout will be significantly lighter when fully cured compared to how it looks when wet.A Notable Exception: Lighter Blues
There are a few notable exceptions to the rule of gray grout being best. The most obvious exception is when you are using gray tile (duh), but the one that usually catches people by surprise is when tiles of lighter blue colors are used. Unfortunately, these are just the shades of blue that are popular for water and sky elements, so this is a significant exception. In this situation, a warm light brown or sand colored grout might be a good choice for contrasting the blue tile, but what if there are light brown tile used elsewhere in the mosaic? Is there a good standby color of grout for this situation? The answer is no, but there is a quick solution.Go Look At Grout Colors With Your Tile
Building material stores such as Home Depot and Lowes usually carry about 30 or more colors of grout, and they have color swatches on the shelves and/or packaging so that you can pick out grout similar to how you pick out paint, only with much more limited options. The trick or tip is to not to try to do this from memory without the benefit of having your tile with you. Take one or two tile of each color used in the mosaic with you to the store and hold them up against the color swatches. I have even gone into the store with small mosaics, just as I have taken in parts of plumbing I was trying to match or replace. Don’t be self conscious about it. The people who work there are accustomed to seeing professionals at work, and you will be quite unobtrusive compared to the building contractors dealing with emergencies. At least you won’t be covered in dirt and holding a toilet seat or something like that.Some “Advanced” Tips
From the many emails and pictures I have received in the past 12+ years, I can state with some confidence that novices tend to regret choosing grout colors as an attempt to add another color to the mosaic. Matching grout color to tile color tends to be even more disastrous.
If you already have your figures rendered in tile using a relatively small grout gap, and you like how those figures look, then your main objective while grouting should be to not mess up the visual art that was already working, especially if you are a novice at mosaic.
Of course, even a novice can take a few of each color tile and create an abstract experiment on a scrap piece of plywood and try a novel grout color on it.
The monochromatic nature of medium gray grout makes it contrast colors intrinsically, in the same way that back and white contrast colors intrinsically. All three are balanced in hue. The keep-it-simple and less-is-more principles really come into play when you decide to second guess some shade of medium to dark gray when grouting figurative mosaic artwork.
On the other hand, there are all those earth tones to play with…
Just remember to experiment on a piece of scrap before trying it out on a mosaic where 90% of the work was spent cutting and mounting the tile.