What is slate, and does it belong in a bathroom?

How does slate form, and where is it quarried?

Slaty cleavage runs perpendicular to the direction of compression, not along the original sediment layers. Fresh cleavage surfaces look dull, and the mica layers inside are typically under 100 micrometers thick.

Spain produces about 90% of Europe's roofing slate, and Wales, Cornwall, Cumbria, France, Belgium, Italy, Portugal and Germany also quarry it. In North America the main sources are Newfoundland, Pennsylvania, Virginia, Vermont, New York and Maine. Brazil is the world's second-largest producer, mainly from Minas Gerais, and China and Australia also hold deposits. A stone-care maker adds that Vermont slate is typically smoother, denser and one color, Brazilian slate dense and hard, and some Indian and Chinese slates soft enough to flake or powder under foot traffic.

What colors and finishes does slate come in?

Slate is often gray, but it also occurs in purple, green and cyan, and North Wales slate runs from pale to dark gray and can be purple or green. Red tones come from iron, which a stone-care maker says can keep worsening unless the stone is treated with a lasting water repellent. One tile importer lists more than 25 colors.

Finish changes both look and behavior. Cleft or riven faces keep the natural split texture and give the most grip. Honed or sawn faces are smooth and flat. A flooring guide says honed finishes reduce flaking, while another trade source says some soft slates with cleft finishes begin to disintegrate in water.

Does slate work on bathroom floors and shower walls?

On floors, yes, with conditions. Riven slate gives traction and hides water marks, and small mosaics on a shower floor help slope and drainage. Behind the tile, a waterproofing membrane is not optional in any wet area. Check with a licensed installer and local code for your substrate and floor load.

On shower walls the limits are real. Slate has two lines of weakness, cleavage and grain, and cleft faces can spall, which means small pieces flake off. A stone-care maker says some small pieces may break off in the first three months. The tile setter quoted in Journal of Light Construction adds that keeping porous slate sanitary is hard and that topical sealers can yellow and chip.

Is slate slippery when wet?

It depends on the face. Riven slate has a rough, natural texture that grips and hides water marks, which is why flooring guides recommend it for wet floors. Honed slate is smoother, and polished slate is the least suited to a bathroom floor because it reduces traction.

Slip behavior also changes with sealer. The tile setter quoted earlier warns against topical coatings on slate, and a topical film can change traction. Ask the supplier for a wet dynamic coefficient of friction on the exact tile, and keep a small mat at the shower exit.

Does slate need to be sealed in a bathroom?

Yes for most slate. A stone-care maker says slate must be sealed to limit staining, that untreated slate will not release stains fully, and that it should be resealed yearly. Its test is simple: pour water on the surface, and if a dark area remains after 10 minutes, seal it.

Use a penetrating, oil-repellent sealer rather than a surface coating. Dense honed slate can resist sealer altogether, which is a sign it is already tight. Clean with a pH-neutral stone cleaner, and keep pressure washing below 800 psi where it is used at all. Slate does not react to acids the way marble does, so etching is not the main concern, but abrasive grit and harsh scrubbing are.

How do you tell slate from stones that look similar?

Dark honed slate is often mistaken for basalt, soapstone or black granite. Slate splits into sheets and shows fine layering on a cleft edge. Basalt is an igneous rock cooled from lava, so it has no layers and a denser, more uniform look.

Soapstone is far softer and feels waxy, because it is mostly talc, which the Mohs scale defines as 1. For a dark stone that behaves differently, see Nero Marquina, a black marble that etches in acid where slate does not.

Does Pietra Fonte make pieces in slate?

We don't currently offer slate. We carve marble, travertine, onyx and a small range of other stones to order. Browse the stone library for what we do work in, or talk to us about a one-off piece through bespoke.