How to Install Tile Over a Tar Paper Concrete Floor
Concrete can make the ideal subsurface for laying tile over if properly prepared. A concrete slab is strong and durable, leaving little cause for concern as to its ability to support even heavy stone tiles. The slab also has fewer movement-related issues when compared to a wooden subsurface, causing less stress to the tiles over time from weather-related expansion and contraction. One drawback, however, is in how moisture affects concrete. Moisture can leak readily through your slab into the tiles unless you place a vapor retarder between the surfaces. A layer of tar paper serves this purpose. Placed between the concrete and the tile, the paper protects the tile from moisture that could degrade the bond between the tile and the concrete.
Clean the surface of the concrete, first by sweeping away any loose dirt or debris and then by mopping the surface with a pH neutral cleanser. Wash any oil or grease from the floor with a concrete degreaser, rinsing away cleanser residue with clean water. Allow the floor to dry completely after cleaning before proceeding further.
Check the level of the surface with a level bar. Drag the long flat side of the level bar across the surface of the slab while looking beneath the bar for any high or low areas in the slab. Mark these areas with a pen for later leveling.
Grind the high levels of the slab down to the level of the surrounding concrete with a concrete grinder. Sweep away the ground concrete. Fill shallow dips in the slab, one-eighth of an inch or less, with self-leveling compound. Spread the compound so that it is even with the slab’s surface using the flat of a trowel. Fill deeper depressions in the slab with concrete mortar. Level the mortar with the trowel so that the depression is also level with the surrounding slab.
Clean out concrete cracks with a wire brush and then fill the cracks with concrete joint repair. Push the repair material into the cracks with a putty knife, and then drag the knife across the surface of the filled crack to scrape away excess material and level the patch out. Wait overnight for the material used in both the leveling and repair process to dry.
Spread a row of asphalt mastic along the edge of the slab that is the width of your tar paper, using the flat of a notched trowel. Tilt the trowel to a 45-degree angle and go over the mastic with the notches to raise ridges in the mastic. Let the mastic set for 30 minutes.
Roll a layer of tar paper over the mastic, butting the ends of the paper together where needed to get complete coverage of the mastic row. Spread another row of mastic alongside the first and repeat the coverage process with the tar paper, only overlap the edges of each row by four inches.
Spread a layer of mastic onto the placed tar paper, notching the surface as you did with the underlayer.
Mount the tiles directly into this layer of mastic, pressing the them down firmly to ensure complete coverage of the tile rear. Place tile spacers between the tiles to allow for even rows and grout lines. Leave a quarter-inch space around the edges of the tile surface between the tile covered floor and the wall for expansion. Allow the mastic to dry overnight.
Remove the tile spacers and grout the tiles. Spread the grout over the tile using a grout float to push the grout firmly into the joints between the tiles. Wipe the surface of the tiles with a damp sponge to remove the excess grout from the tile surfaces. Wait two hours and then go over the surface of the tile with a clean lint-free cloth to remove any remaining grout. Allow the grout to cure for 36 hours.
Brush a layer of tile and grout sealer over the grout to protect the material from staining.