The typical options for tile underlayment are plywood, cement boards and isolation membrane. Properly preparing the subfloor is key to any success tile floor covering project. Here are the steps required to sucessfully install plywood, cement boards and isolation membrane underlayments.

How to install Cementboards

Cementboards can be used for ceramic tile and vinyl floor coverings. Cement boards are better than plywood, especially when the thickness of the underlayment is a concern. It provides far better support for the same thickness.

  • Spred thin-set mortar strating at the longest wall using a 1/4″ notched trowel
  • Set the cement board on the mortar with the rough side up – make sure the edges are offset from the subfloor seams
  • Fasten the cement board using 1 1/4″ cementboard screws every 6″ at 8″ intervals in the filed of the cement board – make sure to flush all the screw heads with the surface of the boards
  • Cut cement board as required to follow the surface of the floor – make sure to leave 1/8″ gaps at all joints and 1/4″ around the walls
  • Place fiber glass mesh over the seams and fill all the gaps with thin-set mortar by using a putty knife
  • Allow the thin-mortar to cure per maufacturer’s instructions before starting tile installation.

How to Install Isolation Membrane

If ceramic tiles are installed on cement floors, installing an isolation membrane is the best solution to protecting ceramic tiles from movement of the cement floor.

  • clean the cement floor
  • apply thin-set mortar with a 1/4″ notched trowel – some membranes require a special bonding material instead
  • roll-out the membrane and cut its edges with a utility knife
  • Smooth out the membrane with a heavy floor roller – start from the center of the membrane to allow air trapped underneath to escape
  • continue with the next membrane – do not leave any seams between membrane sheets
  • Allow mortar or bonding material to cure per manufacturer’s instructions before installing the tiles.

For plywood underlayments, please follow the steps outlined in our earlier article “How to Install Plywood Underlayments”

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