Leveling a Concrete Subfloor with Isolation Membrane


Leveling a concrete sub floor with an isolation membrane is an easy way to increase the usability of the area while adding comfort to the subfloor. The only thing to remember when accomplishing this task is to level the sub floor and clean the entire area before laying the isolation membrane down, otherwise the floor will still be uneven and could have sharp objects protruding through it. This is a task that can easily be accomplished within a few hours, so instead of hiring a professional contractor gather up the following tools and materials, roll your sleeves up, and get to it.

Tools and Materials Needed:

  • Isolation membrane
  • Broom
  • Concrete filler
  • Level
  • Spray paint
  • Stiff wire brush
  • Putty knife
  • Thin set mortar
  • Trowel

Step 1 - Clean the Area

Begin this process by cleaning the entire area with a broom. All large particles need to be removed from the surface of the sub floor. If mud or paint has accumulated on it, then they will have to removed with a stiff brush or putty knife. If you have a multipurpose vacuum it would also be a good idea to use it after the sweeping has been done to ensure that all debris has been removed.

Step 2 - Check for Level

Walk around the entire area with the level placed flatly against the sub-floor. Any areas that are not level need to be marked with spray paint. If the floor happens to be higher in some places chip that section out because it is easier to fill in holes than it is to raise the entire floor up to level.

Step 3 - Apply Concrete Filler

Mix the filler (a self leveling variety) according to the directions given and begin filling all the areas that have been marked with spray paint. Use the level to ensure that you get the correct amount within the holes. Allow this filler to dry before continuing on to the next step.

Step 4 - Install the Isolation Membrane

Cut pieces of the isolation membrane to fit the length and width of the holes or cracks, and set them into place on top of a bed of thin set mortar. Cover the membrane with a layer of mortar and use the trowel to feather out the edges of the isolation membrane to ensure that it is level with the surrounding sub floor.

Repeat this step for all of the cracks and holes that need to be filled. Before walking on the surface make sure that the mortar has had plenty of time to dry and set properly.

Step 5 - Finishing Up

The reason for adding the isolation membrane into the cracks and the holes is to add strength to the floor while allowing it to be leveled. The low spots do not need to have isolation membrane added into them because the self leveling filler will work for such cases. However, cracks and large holes need to have the membrane installed otherwise the sub-floor will not remain level for long, and the holes and cracks could reappear within a matter of months.