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Mosaic Grout

There is nothing unique about mosaic grouts. The grouts and sealers used for mosaics are the same ones used for ordinary bathroom tiling, and the techniques of applying are the same. To learn more about grouting techniques, ask at you local building material store or look at a basic book on home improvement if you need pictures.

Estimating how much grout is needed

How much grout you need depends on three things: the area of the mosaic = L x W, the thickness of the tiles and the gaps between the tiles. If the tiles well-spaced (all gaps under 1/4"), then you should be able to cover the entire mosaic of 18" x 18" with 2 lbs of grout. This is assuming your tiles are under 3/8" thick. I always set my mosaic on an old shower curtain or piece of plastic to catch all the wet grout that falls off the side as I'm spreading it. That way, I can scoop it up and use it. Otherwise you need a lot more grout because most is wasted.

If the gaps between your mosaic tiles are greater than 1/8" then you may need grout with sand in it. The sand reinforces the grout to prevent cracking if the gaps are greater than 1/8 inch.

How to grout a mosaic

Mix the grout according to instructions on package and avoid breathing dust. Spread the grout into the cracks. Wipe off the excess grout. Use a sponge instead of a rag because the rag will catch on any sharp edges. Don't try to wipe it perfectly clean all at once. Rinse out the sponge after each pass. Make sure your sponge isn't dripping water after you rinse it out. Wipe flat across the surface. Don't rub down in the cracks or you will erode the grout between the tiles. Keep the surface damp as the grout cures or it will crack. Return to Top

Selecting a grout color

I always choose a grout color which contrast the colors of the mosaic tiles so that the design is highlighted. Otherwise the individual tiles are lost to the eye, and the mosaic looks more like an ordinary picture and less like a mosaic made from pieces. I avoid situations like gray grout with gray tile. A nice red-brown grout works better in that instance. The key concept is color contrast.

Color is best provided by the tile, not the grout. In terms of a visual element, the grout is supposed to act like a thin gray pencil line that just makes each tile distinct. I don't think I've ever seen a mosaic that used colored grout that wouldn't have looked better if all tile had been used instead. For example, let's say you wanted red tile in pink grout. A better way to get the same color effect would be to mix in a few pink tiles randomly throughout the red tiles, or maybe use a few lines of pink tiles. Often this means you have to cut your tile just a little bit smaller.

There are mineral concrete dyes sold at building material stores, and these can be used, although the range of colors is limited to black, brown, gray, terracotta, etc. Vegetable dyes such as food colors will not be permanent.

The best color grout to use overall is medium-gray. Here's why: The purpose of grout in visual terms is to make each tile distinct like a gray pencil line in a watercolor. A medium or "natural" gray provides just enough contrast to most colors, unless you have gray tile, and then you might want to consider black or a dark gray. Avoid pure white unless you are trying to make something that looks like a little kid's summer camp project. Most building material stores such as Lowes and Home Depot cary about 30+ colors of grout. Bring a few of each color of your tiles with you, and you can pick the color grout that works best with all the tile.

Grouting stone tile and unglazed ceramic

If after grouting your mosaic, the stones turned the same color as the grout, it may be because you did not seal the stones. You should always seal stone tiles and unglazed ceramic tiles with a tile and grout sealer BEFORE you grout. This is necessary for all porous materials that can be stained by grout. You should seal using a Stone Enhancer instead of tile and grout sealer if you want to darken and enhance the natural color of the stone. Both of these products are available at local building material stores. Ask there. For a stone mosaic that is already stained, you might want to try some of the muratic acid that contractors use to clean cement from bricks. Also ask at the building material store about this product.

Cracking and crumbled grout

You shouldn't let the grout dry out as it cures. Lightly mist with a spray bottle, but don't let drops accumulate on the surface of the mosaic. Mix the grout according to instructions. It should be like a thick moist dough when you start with no dry material or lumps, and it should stick to your mixing wand, not drip, slide or crumble off.

With sanded grout, if there was too much water in the grout mixture, when the water evaporates, the remaining grout may not be dense enough, which leads to cracks or crumbly grout. With premixed unsanded grout, the most common reason for cracking is too-large grout lines. This grout will shrink when it dries, so if the grout lines are too wide, the grout will no longer fully fill the space between the tiles.

Disposal of grout waste

Never pour grout down your drains. Grout is concrete and that isn't good for your plumbing. It will clog the pipes. I always just dilute the grout water and pour it in on my compost heap. The grout is a limestone product, so it actually helps balance the pH when there is excess decaying organic matter. Of course, this only applies to traditional grouts. I am not familiar with the synthetic epoxy grouts that some craft sites are selling. For easy cleanup, I always do my grouting in the backyard instead of indoors.

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