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Installing Heating Cable and Schluter® DITRA-HEAT Uncoupling Membrane



Using a thin-set mortar that is suitable for the substrate, apply the thin-set mortar (mixed to a fairly fluid consistency, but still able to hold a notch) using a 1/4" x 1/4" square-notched trowel.

Apply DITRA-HEAT or DITRA-HEAT-DUO to the floor, fleece side down. Solidly embed the matting into the mortar using a float, screed trowel, or DITRA-ROLLER, making sure to observe the open time of the bonding mortar. If the mortar skins over prior to matting installation, remove and reapply.Note: It may be helpful to back roll the end of the matting before installation, or place boxes of tile on top of the matting after installation, to avoid curling.
Lift up a corner of the matting to check coverage. Proper installation results in full contact between the fleece webbing and the thin-set mortar. Note: Coverage may vary with mortar consistency, angle at which the trowel is held, substrate flatness, etc. If full coverage is not achieved, remove and reapply, making sure to verify proper mortar consistency and application.
Abut end and side sections of adjacent sheets. Note: Aligning the studs on the top of the matting during installation can help make subsequent heating cable installation easier.
Estimated thin-set coverage.
  • To bond DITRA-HEAT to the substrate: Use one 50 lb. bag of mortar per 100 S.F.
  • To bond the tile to the DITRA-HEAT, using a 1/4" x 3/8" square or U-notched trowel: Use one 50 lb. bag of mortar per 40 - 50 S.F.
  • To bond the tile to the DITRA-HEAT, using a 1/2" x 1/2" square or U-notched trowel: Use one 50 lb. bag of mortar per 30 - 40 S.F.
Before the heating cable is removed from the spool, conduct the first set of required tests and record values in the heating cable tests log in the installation manual. If a break or damage is detected during the tests, contact Thermosoft customer support.
Thread the heating cable cold lead through a conduit (where required by code) from the base of the wall to the thermostat electrical box. Floor temperature sensors may not be threaded through the same conduit as the cold lead.
Mark where the cold/hot splice will be placed, cut the DITRA-HEAT or DITRA-HEAT-DUO matting, and insert the splice. It may be necessary to temporarily secure the splice to the floor with thin-set mortar or adhesive (hot glue). Once the heating cable cold lead and remote sensors are threaded to the thermostat electrical box, install a metal protection plate at the base of the wall. This will help prevent any damage from fasteners (e.g., nails, screws, etc.) in the future.
Embed the heating cables between studs, at a spacing of 3 studs (3-1/2"). Closer spacing may result in overheating and damage to building structures. A wider spacing (e.g., 4 studs) will not provide sufficient power to warm the floor to the desired temperature. Exception: a two-stud spacing is used when connecting the 240 V cable to a 208 V power supply.
Use care not to damage the cables during installation, particularly before the cables are embedded in the matting.
The maximum allowable length of a single run is 5 ft.; the cable must be turned or a u-shaped "jog" created at this point (see image).
Install the thermostat sensors evenly spaced between two cable runs, at a distance of at least 24" from the wall. Mark the sensor location on the DITRA-HEAT and cut the matting to recess the sensor. It is recommended to temporarily remove the heating cable from the area while cutting the matting. It may be necessary to temporarily secure the sensor to the floor with thin-set mortar or adhesive (hot glue). Embed the sensor wire in the matting without overlapping or crossing the heating cable.
Once the heating cable and floor temperature sensor installation is complete, retest and record values in the heating cable tests log.
Waterproofing: The following 4 steps are required for waterproofing only.

Note: While the heating cable is protected by the DITRA-HEAT and DITRA-HEAT-DUO matting, be careful when applying the mortar to not damage the cable with the notched trowel. At the joints, fill the matting with unmodified thin-set mortar, approximately 8", centered over the joint.
Comb additional unmodified thin-set mortar over the joint using a 1/4" x 3/16" V-notched trowel or a 1/8" x 1/8" square-notched trowel.
Apply 5" wide KERDI-BAND, centered over the joint. Using the flat side of the trowel, firmly press the banding into the mortar to ensure 100% coverage and to remove excess mortar and air pockets.
At all wall junctions, apply KERDI-BAND as described in steps 1-3, centered where the wall and floor meet. In some applications the vertical section of the floor/wall transition will not accept a bond to unmodified thin-set mortar. Connections to such elements can be achieved using KERDI-FIX sealant and bonding compound or suitable trowel-applied waterproofing materials, such as those that require atmospheric moisture to cure (e.g., urethane sealant). Note: KERDI-BAND must lap DITRA-HEAT and DITRA-HEAT-DUO at seams and at floor/wall transitions by a minimum of 2" in order to maintain waterproof integrity.
Tiling
Note: While the heating cable is protected by the DITRA-HEAT and DITRA-HEAT-DUO matting, be careful when applying the mortar to not damage the cable with the notched trowel.
Tile can be installed over DITRA-HEAT and DITRA-HEAT-DUO immediately; no need to wait for the mortar to cure. Fill the matting with unmodified thin-set mortar and comb additional mortar over the matting using a trowel that is appropriate for the size of the tile.
Solidly embed the tiles in the setting material, making sure to observe the open time of the bonding mortar. If the mortar skins over prior to tile installation, remove and reapply.
Periodically remove and check a tile to ensure that full coverage is being attained.
Once the tile installation is complete, retest the heating cable and record values in the heating cable tests log.
Allow the assembly to cure for 7 days after grouting before putting the floor warming into service.
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