Tiling using slate can be very difficult due to the often random thickness of the edges of the tiles, obviously this can make the job much harder than using most other types of natural stone tiles.

Choose the colour of grout very carefully when using slate tiles as light colour grouts can make imperfections stand out like a sore thumb

Adhesive for slate tiles 

Choose an adhesive that is suitable for your particular application. If you are tiling onto a wooden floor you will need a flexible floor adhesive. Tiling a floor

Cutting Slate tiles

 slate tiles are best cut with a diamond wheel cutting machine Wet tile saw although you can use an angle grinder if you don't have a wet tile saw.

Drilling Slate Tiles

Slate tiles can be drilled with a standard tile drill but best results can be achieved with a Diamond coated drill bit / hole saw - Tile drilling | Diamond coated hole saws

Fixing Slate tiles

Lay the slate raw (Don't seal it first) and allow it to dry for at least 24 hrs, during this time if any white residues appear on the surface of any of the tiles, this is efflorescence, there are ways of removing it, but over the years I found it was far less hassle just to chop the tile out and replace it at this stage. Once it's all dry (and before you grout) seal it thoroughly, If you want a dull dusty finish as the slate appears raw then a product called Lithofin Stain Stop MN is your choice. If you prefer the enhanced colour of the slate as it appears when a damp cloth has been wiped across the surface, then Lithofin Slate Seal is the product you need instead of Stain Stop.

Grout with your choice of colour, with a black slate grey looks good, either BAL wide Joint or Ardex C2. However you might want to consider black grout or Ardex C2 Anthracite, which give a very nice appearance to the overall floor, and hide far more imperfections than a grey grout would. If the slate is machine cut give yourself at least 5mm joints Finishing Grout with your choice of colour, with a black slate grey looks good, either BAL wide Joint or Ardex C2. However you might want to consider black grout or Ardex C2 Anthracite, which give a very nice appearance to the overall floor, and hide far more imperfections than a grey grout would.

If the slate is machine cut give yourself at least 5mm joint. If the stone has split or rustic edges you'll need up to 20mm joints, in which case use Ardex C2 grout as it sets far harder than many alternatives and goes as wide as 25mm without a problem.

Once grouted clean the surface with an emulsifying pad (Big plastic pan scourer) let it dry at least 24hrs and the reseal the whole lot again including the grout.