Slate and other stone floors don’t need to be sealed, though if left open they are porous and exposed. Too much moisture can stain the stone, so it is recommended that even if you don't seal all of your slate floors, you at least seal those parts in high traffic areas. Once sealed, slate floors will periodically need to be resealed, perhaps every one to two years. To tell if your floor needs to be resealed, put a drop or two of water on the stone; if it beads, then the seal is still intact, if it is absorbed, then you should reseal the floor.
How to seal your slate floor
This is a job that can be managed yourself. There’s no need to call in professionals, provided that you have the time and motivation to tackle the job. All you need is the sealant, a paint tray and a roller to apply it with. Before you start, check the application method listed on the sealant to ensure that you're applying it properly. The method below is an example of how it's normally done.
To start, mop the floor thoroughly and allow it to dry fully. Next, make sure the room is well ventilated, and pour your sealant into a paint tray. Start rolling the sealant on from one wall to the other horizontally across the room, making sure you don't paint yourself into a corner.
Allow the sealant to dry for the amount of time recommended by the manufacturer. Next you need to apply the second coat. Apply this coat vertically across the room this time, and allow adequate time for it to completely cure before you use it. This ensures that the floor will be kept in prime condition for longer.
How to fix scratches on slate
Most scratches on sealed slate floors can be repaired fairly simply. Superficial scratches can often be removed with a purpose-designed sealer solvent. In most cases, it's simply a matter of applying a small amount of sealer solvent, and working it in gently with a cloth or a scrubbing brush. Depending on how many times you do this, you may also need to reseal your floor to compensate for the solvent removed in the process. In most cases, using sealer solvent will remove or conceal scratches and marks on slate tiles.