Schluter Underlayment Costs $70 to $2.20 per Square Foot to Buy
Schluter Ditra tile underlayment is more costly than cement backer board (CBU), but it offers the benefit of adding a layer of waterproofing between the tile and underfloor substrate, making it useful for spaces like bathrooms or kitchens. Ditra is additionally more elastic than CBU, permitting greater substrate movement and preventing potential stress fractures and cracks.
January 10, 2023, by: Rob Parsell
To help you decide whether Schluter-DITRA underlayment is the best option for your tile project, we have provided detailed information on this popular underlayment in this tile installation report. Click here to learn more about purchasing, setting up, paying for, and maintaining tile and stone floors.
DITRA VS. CBU: WHICH MATERIEL IS RIGHT FOR YOUR PROJECT?
Let’s compare the benefits and drawbacks of each material side by side.
Standard DITRA is 1/8” thick, and this helps to eliminate height differences where two different flooring materials meet; CBU is twice as thick at 1/4″.
DITRA is fully waterproof; CBU allows water to pass through it, but is not damaged by the water. DITRA is the right choice when installing flooring over concrete or other material that requires a moisture barrier to prevent damage to flooring.
DITRA, as a decoupler, helps prevent substrate movement from damaging flooring; When using CBU, the tile is mortared directly to the board, and expansion or shifting of the subfloor is likely to crack or pop the tile or grout.
DITRA offers faster, easier installation than cement backer board, especially when the project requires a large amount of trimming around obstacles such as support posts, drains, bathroom fixtures and door jambs.
Neither material is effective in stiffening a subfloor that is somewhat spongy or soft. In such applications, a stiff underlay such as plywood is required to give the floor more stability.
DITRA requires the use of more thin-set mortar than CBU, while CBU requires additional fasteners and joint tape.
Schluter recommends the use of its specially-designed trowel for the application of mortar used to install DITRA, but it is not essential.
The underside of the DITRA membrane contains free spaces between the cavities. These spaces allow excess moisture and vapor to escape, reducing the potential for it to damage the layer of tiles above. CBU structure does not offer this protection.
ADDITIONAL STEPS FOR WATERPROOF APPLICATION
The next step is to cover the seams with an 8″ wide layer of unmodified thin-set centered on the seam after the DITRA membrane has been installed but before any tile is set. It must fill all of the cavities.
Next, use a 1/4″ x 3/16″ trowel or the Schluter KERDI trowel, which has a 1/8″ x 1/8″ square-notched design, to apply and comb a top layer of unaltered thin-set.
To ensure solid mortar coverage to the back of the Schluter KERDI-BAND, lay a 5″ wide strip over the seam and press it down firmly with the flat side of your trowel to remove air and extra mortar.
Use a 10″ wide strip of KERDI-BAND in the corner, centered, to ensure a waterproof seam where the wall meets the floor. Follow the same procedure as described for waterproofing seams.
Here’s a tools and materials list for installing DITRA matting:
DITRA or DITRA-XL depending on the requirements of the job
DITRA-Set mortar or similar thin-set mortar
DITRA trowel or other suitable option (see Step 2 above) for applying mortar to the substrate
A 1/4″ x 3/8” trowel for applying mortar to the top of the DITRA for tile installation
Utility knife for cutting the DITRA underlayment
Chalk line for laying out the DITRA (optional)
Flat trowel
Grout float
5-gallon mixing pail
Mixing paddle
Electric drill – A hammer drill with a handle works best
Tips on Schluter®-DITRA-HEAT under Alternative Floor Coverings
Here’s a tools and materials list for installing DITRA matting: