Thinset Over Painted Floor

The polymer modified thin set mortars might bond to a latex paint but not an oil based paint.

Thinset over painted floor.

Not that they would endorse going over an oil based paint what you should do is scarify the paint off the floor. The floor is a 4 inch poured concrete slab over an unheated utility room. Installing tile over painted concrete adds a few extra steps to your tiling job. First a surface more textured and solid must be applied over the painted concrete.

All paint will need to be removed before you begin installing the tile. The house was built in the late fifties and the slab floor has been painted at least once. Mortar cannot be installed directly over painted concrete itself. Whether you have cracks chips or just a stained concrete slab thinset helps cover the old surface and create a new problem free area.

It must be easy to work with and it must adequately fill in gaps between the tile and the substrate. Tile cannot be attached directly to painted concrete as the thin set will not adhere well to the paint. Tile will stick to most rigid level surfaces including painted wood provided the correct preparation work is done to ensure the adhesive or mortar will stick to the floor surface. It cannot cure too fast.

Otherwise you do. This surface is called a scratch coat. The safest way to approach questionable concrete is not to cover it over with cbus but to fix the concrete. Whether wall or floor tile that tile needs to thoroughly stick to its base surface demands placed on tile adhesive are both extensive and steep.

A scratch coat will give the mortar something to hold on to instead of the layer of paint over concrete. Paint used on concrete will not bond with the tile adhesive. Unfortunately the tile cannot be adhered directly to the painted surface. Mapei ultrafor plus data sheet says to use their keraply latex admix in lieu of water when going over impervious surfaces.