Installing Slate in Bathrooms

Sure, slate tile requires a little more maintenance than ceramic or porcelain tile, but its unique colors and textures are appreciated by many homeowners. Slate tile installations owe their warm, rustic appearance to the fact that the tiles are natural stone, and so will vary in color and texture from one tile to the next.

For installing slate in bathrooms, one of the most important factors is selecting the correct type of slate. Slate types include New England Slate (from the Slate Valley area of Vermont and New York), Brazilian, Welsh, (which varies in hue from green tint, to purple, to blue to brown and to black) Chinese, African, Indian, and Portuguese slate. You must select for your bathroom a slate type which will accept a moisture and stain resistant sealer, and for use in shower stalls and tub surrounds, a type which will not degrade due to constant moisture exposure.

Best Slate Tile Types

Typically, domestic slate from Vermont as well as the Brazilian and Italian slates, come with a honed finish. These slated are a very dense material and so stains are only superficial. The drawback is it does not absorb an "impregnator"-type sealer well. In fact, most domestic slate tile producers recommend to not seal it. If you want to apply sealer to it anyway, for whatever reason, then test a small area of the slate tile first. You do not want to spoil the natural look of the stone, it's best characteristic.

Shower stall and tub surrounds: find out what type of slate you are buying, from where? Not all slate is acceptable for water exposure applications. Take a home sample piece and place it in a bucket of water for a while and let it soak. Then scrub the tile with a scrubbing pad. If the water turns muddy and the slate looks like it's falling apart, don't use it in the shower, go with something else on your walls like ceramic.

Good slate that can be sealed is fine for a shower, but don't use it on a shower floor. Instead, use dark-colored porcelain 2x2 tile there; slate is just too high maintenance, needs sealing, absorbs moisture and tends to be a little too slippery. One drawback to be aware of with using slate for shower walls is it is a dark material and can make a shower stall seem like a dank, dark cave if the lighting is not right.


Another key to a successful tile installation is having an underlayment, or subsurface, that is stable, particularly for floors. In general, cement backerboard is a good underlayment for natural stone tiling. Your main issue for flooring is not supporting the weight of the stone, but in the amount of deflection, or flex in your floor. This will depend on the joist spacing. The wider the spacing of the floor joists the stronger the likelihood it that the floor will move up or down as it is walked on it and as it shifts due to expansion from temperature or humidity changes.

For joist spacing of 16" inches to center, use a 1/4" underlayment over your sub-floor. If it is 19.2" inches on center you can use either a 3/8" or 1/2" material, if it is 24" inches on center then you will probably need 3/4" material.


It's a matter of design style, but slate tile is usually installed in bathrooms using wide grout joints. Try 3/8" for the 12"x12" size tiles and 1/2" grout width for the 16"x16" tiles. Because of the subtle variations in tile sizes using tile spacers is not recommended with slate tile. After grouting, you may find a slight haze on the tiles; this can be caused by the grout. Some installing try to prevent grout haze by presealing the tile.

However, the best method is to do a good job cleaning the grout off your tiles as you go along. A microfiber cloth works wonders for this. Keep a damp tiling sponge handy also to work out any grout that catches in crevices. Wait for the grout to dry and then seal the tiles and grout all in one go.

The exception to this method is if you are picky about your grout coloring. Some of the enhancing type sealers will darken grout or give it a glossy, wet look. If this is a concern, then pre-seal your tiles before the installation. But be careful not to get sealant on the surfaces of the tile you want the grout and mortar to adhere to.

See Also:

How to Seal Grout