Should a penetrating or topical sealer be used for slate floors?
If you have slate floors, in most cases, you should use a penetrating sealer to protect them. A penetrating sealer will get deep down inside the slate and fill up any of the spaces in the porous stone.
A topical sealer will only provide a membrane that protects from the top, and it can easily wear off because it is on the top layer where you walk. When this happens, the sealer does not offer any protection for the slate tile. Because slate is so porous, it needs a sealer that will penetrate its holes to protect it from staining.