Apply more of the sealant you wish to remove to the slate or affected area. Sealants can emulsify themselves if the first application is fresh enough.
Paint the new layer of sealer over the old with a foam paintbrush. Wait for 10 to 15 minutes and then begin wiping with a lint-free cloth.
If the sealer is emulsifying, but still tacky, apply more and wait longer.
Apply sealant stripper to the affected area with a foam paintbrush. The stripper will remove all layers of sealant from the stone.
Wipe up the stripper and the sealant with a lint-free cloth.
Clean the slate well with a stone cleaner. Stone cleaners are available in spray bottles.
Spray the cleanser on the stone, and buff with a lint-free cloth to remove any residue from the stripper or sealer.