How to Adhere Slate Over Tile

Clean the surface of the existing tile installation completely to prepare it for a new tile installation. The thinset mortar cannot bond through layers of grime, grease, dirt and other buildup over the years, so you need to get the tile as clean as it was on the day it was installed. Use a professional flooring machine with an all-purpose cleaner to scrub the surface clean.

Rough the entire surface of the existing tile installation with a professional floor sander, also known as a drum sander. Tiles are generally glazed, making them a polished surface that is difficult for the thinset mortar to bond with. The surface needs to be scratched or roughed up. Clean the area completely with a commercial vacuum cleaner designed to be used with construction and heavy duty dust.

Prepare the installation surface. Mix up a batch of thinset according to the manufacturer’s instructions on the bag and skim coat the entire installation area. Use the flat trowel to apply pressure as you spread the thinset across the floor, filling in the old grout joints and backfilling everything so you have a totally flat surface ready for the slate tile.

Install your slate tile as you would in any other type of tile installation after the skim coat layer has dried for a minimum of 24 hours. Lay out your installation area, spread thinset mortar on top of your old floor with an appropriate-sized trowel depending on the size of your tile and adhere the slate to the bed of thinset mortar.