Slate, a very dense but soft material with low porosity, can be used effectively outdoors as well as indoors. Slate is a fine grained metamorphic rock formed by the metamorphism of shale and clay under lower pressures and temperatures which tends to split into sheet-like (cleavage planes) structures formed in response to differential stress. It comes in a multitude of colors and has two lines of breakability (cleavage & grain).
Composition: Mainly grains of mica and quartz, plus smaller amounts of chlorite, hematite, and other minerals. Most slate is gray to black, but the rock may be red or purple, depending on its mineral content. The surface of slate is generally uneven and cleft planes can spall, due to the cleaving of the stone along its layers. Has low to medium absorption of oils and other liquids. Should be sealed with an oil-repellant penetrating sealer to prevent staining and reduce soiling. Because of the cleft planes and strong possiblility of spalling, it should never be cleaned at pressures above 800 PSI and then only if the grout is in good condition.
Vermont type slate is typically smoother, denser, one color (red, green, black, blue). Indian and Chinese slates are dense and soft, of all colors and variegated colors. Brazilian slate is typically dense and hard, interesting colors and patterns of color.
Slate is very stain resistant. However, some foods can cause stains. Many people make the mistake of applying heavy waxes or floor finishes that rob the slate of its natural beauty and slip resistance. High Gloss Stone Sealer can also be used where a glossy finish is desired (interior only).
Slate has a hardness of 6 on the MOH Scale (a scale for determining the relative hardness of a mineral according to its resistance to scratching). The hardest mineral, at 10, is diamond. The softest mineral, at 1, is talc.
What are the DO’s and DON’Ts of Slate?
•DO clean up spills immediately to minimize damage to your stone.
•DO use trivets or mats under hot dishes and cookware.
•DO use place mats under china, ceramics, silver and other objects that can scratch your stone’s surface.
•DO use coasters under glasses, especially if they contain alcohol or citrus juices.
•DO clean surfaces regularly with cleaner & protector.
•DON’T wait to clean up spills on stone.
•DON’T use cleaners that contain acid such as bathroom cleaners, grout cleaners or tub cleaners.
•DON’T use vinegar, bleach, ammonia or other general-purpose cleaners.
•DON’T use abrasive cleaners such as dry cleansers or soft cleansers.
•DON’T use alkaline cleaners not specifically formulated for stone.
•DON’T use scouring powders and abrasives because they will scratch the surface.
•DON’T clean at high pressures.
Maintenance Cleaning of Slate Tile
Highly alkaline, acidic, ammoniated, abrasive cleaners and/or bleach may break down the sealer, adversely affecting repellency and may not be good for the stone. Use a neutral cleaner specially formulated for natural stone.
For routine cleaning with protection (not recommended for lacquered surfaces):