Slate is a metamorphic rock. It is formed from shale by being under pressure and moderate heat. Shale itself is formed from muddy clay, and splits into thin plates. This characteristic splitting is carried over into slate.
Slate is a naturally cleft, flaky stone. For the first three months after installation, some small pieces may flake or break off of the tiles. This is called “spalling,” and is a natural process that occurs as the slate adjusts to the new environment. You may notice that the room where the slate has been installed becomes excessively dusty and that there are small chips underfoot.
Sweep the slate daily to help bring up the dust and chips. If you have a vacuum without a beater bar, you can also vacuum daily to help keep down the dust. The spalling will stop once the slate has settled.
Slate is a natural stone, so some acids and alkaline cleaners may etch its surface. Sweep the slate regularly to cut down on surface grit and dust. Wash the slate tiles as needed with either a stone cleaner or a mild detergent with a neutral pH. Do not use cleaners that contain lemon or vinegar, as these can cause etching. Rinse the slate with clean water, and dry polished and honed slates with a soft cloth to prevent water spots.
Slate may show chalky-looking scratches from time to time, particularly in high traffic areas. These can be disguised by applying mineral oil to the scratch and the surrounding area of tile. First, clean the slate well with a mild detergent and dry it thoroughly. Use a soft cloth to apply the mineral oil, rubbing it into the scratch until it disappears from view. The mineral oil will also seal the slate if the stone is porous.
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