Use Isolation Membrane to Tile Over Uneven Concrete

Using isolation membrane to install tile over concrete that is uneven may take a little than it would take to apply it to a backer board made of concrete. Isolation membrane is used on cracked or uneven concrete that needs to be tiled over. It prepares the surface before tile is actually applied to it. If you do not use the isolation membrane before laying the tile over uneven concrete surfaces, the new tiled floor will more than likely crack on the same spot that is already in the concrete floor. If there are expansion joints existing in the slab, the tile will ultimately crack there also. It does not take much work in installing tile over concrete that is cracked or uneven using isolation membrane. The tools and instructions you will need for this job are listed below.

Tools and Materials Needed:

  • Chalk line
  • Hoe
  • Broom
  • Permanent marker
  • 2 by 4 lumber
  • Leveling compound

Step 1 – Cleaning Off Concrete Floor

Use a gardening hoe to scrape away any debris that may be sitting on concrete floor. Once debris has been moved, sweep it using the broom.

Step 2 – Marking the Spots

All of the low or high spots in that concrete floor will need to be marked. Slide the 2 by 4 lumber all over the narrow edge floor. If there are any gaps between lumber and the floor, mark the area as low. Permanent marker can be used for your markings.

Step 3 – Leveling the Floor and Placing the Isolation Membrane

Pour leveling compound over low areas. This will raise these low areas of the floor to become level. After leveling compound has dried, place a thin layer of the isolation membrane onto the middle of all existing cracks which is found in the floor. Use a flat trowel to spread the membrane out. When spreading the membrane, try to work out the tile adhesive excess and feather the edges out. Allow the adhesive to sit overnight to dry.

Step 4 – Laying Out the Tile

To determine the middle point of the design of the tile, lay out one row in two directions. Snap chalk line from the walls facing opposite each other to mark the center. Use those lines to lay the 2 rows at the start. 

Step 5 – Installing the Tile

Move by 2 feet square areas to install the tile. Apply the mortar until it has covered the 2 feet square in its entirety. Take note that the chalk line is not covered.

Step 6 – Lining Up the Tiles

Lay the tile where one edge of it is on the chalk line. Lay the second tile next to the one just laid. This step is to be repeated with the other tiles. Use tile spacers to make sure that the spacing between them remains even. Let tiles sit overnight to dry.

Step 7 – Grouting the Floor

Grout floor and wipe the tile surfaces clean using a damp cloth or sponge. This removes any haze left from the grout. Allow the grout to dry completely, and apply grout sealer.