Sand the textured wall using an electric sander with a medium-grit sanding belt. This will buff down the textures on the wall to create a smooth, even surface.
Vacuum the wall and surrounding areas using a shop vacuum to remove dust and debris caused by the sanding.
Spread a 1/2-inch thick layer of plaster mortar over the surface of the wall using a trowel.
Press 1/4-inch tiles halfway into the mortar, then scrape off the excess mortar using the trowel. Space the tiles 1/4 inch apart.
Spread a 1/4-inch thick layer of fine grout over the surface of the tiles, then scrape off the excess with the trowel. This will push excess grout into the cracks.
Wipe off the surface of each tile using a damp washcloth, then allow the tiled wall to dry for 12 to 18 hours.