Schlüter®-DITRA-HEAT | Substrates | Schlüter-Systems


Substrates for Schlüter®- DITRA-HEAT:

Always check the substrates on which Schlüter®-DITRA-HEAT is to be installed to make sure they are level, load-bearing, clean and compatible with the materials to be used. Remove all surface components that may weaken the bond. Uneven or sloping areas must be levelled prior to the installation of Schlüter®-DITRA-HEAT. To guarantee the effective heating of the floor, thermal insulation must be included in all installations directly above the ground or over unheated rooms. For a faster heat-up response, we recommend the installation of Schlüter®-DITRA-HEAT-DUO with its thermal break property over unheated screed assemblies or the use of Schlüter®-KERDIBOARD as an insulation layer (see data sheet 12.1).


Concrete is subject to long-term form changes due to curing processes. Additional tensions may result from the deflection of concrete and pre-stressed concrete. Schlüter®-DITRA-HEAT uncouples the tensions between the concrete and the tile covering, which means that tiles can be installed as soon as the concrete reaches a sufficient level of stability.

Cementitious screeds

In accordance with the applicable regulations, cementitious screeds must be at least 28 days old and have a residual moisture level below 2 CM% before tiles can be installed. However, floating screeds and heated screeds are particularly prone to curling and cracking, for example because of weight loads and temperature fluctuations. With Schlüter®-DITRA-HEAT, tiles can be installed on green cementitious screeds as soon as they are ready to bear weight. Cracks and buckles forming in the screed at a later time will be neutralized by DITRA- HEAT and will not be transferred to the tile covering.

Gypsum screeds

According to the applicable rules, gypsum screeds may only have a residual moisture level of max. 0.5 CM% when the tiles are installed. When Schlüter®-DITRA-HEAT is used, the tile covering is ready to be installed as soon as the residual moisture level drops below 2 CM%. If necessary, treat the screed surface as recommended by professional standards and manufacturer instructions (sanding, priming). Schlüter®- DITRA-HEAT can be installed with suitable thin-bed adhesive. Schlüter®-DITRA-HEAT protects the screed against permeating moisture at the surface. Gypsum screeds are sensitive to moisture, making it necessary to protect the screed from further moisture, e.g., high humidity.

Heated screeds

Schlüter®-DITRA-HEAT may also be installed over heated screeds, with the above material notes to be observed (cement, gypsum). When Schlüter®-DITRAHEAT is used, the covering assembly may be heated up as early as 7 days after completion. Starting from 25 °C, increase the supply temperature by a maximum of 5 °C a day to reach an operating temperature of max. 40 °C.

Note: The use of Schlüter®-DITRA-HEAT over heated screeds allows for individual, partial warming that is separate from the central heating system. That allows for completely switching off the central heating system during seasonal transition periods. Schlüter®-DITRA-HEAT can also help cover peak loads. Due to the thermal separation property of Schlüter®-DITRA-HEAT-DUO, it is not recommended for use on heated screeds.

Synthetic coverings and coatings

All surfaces must be weight-bearing and be suitable or pre-treated to enable the bonding of a suitable adhesive with the anchoring fleece of Schlüter®-DITRA-HEAT. The suitability of the adhesive for the substrate and for Schlüter®-DITRA-HEAT must be verified in advance.

Plywood panels

These materials are heavily affected by moisture (or major fluctuations in humidity). It is therefore recommended to use plywood materials with special impregnation to prevent the absorption of moisture. In principle, panels can be used as a substrate on walls and floors in interior areas. The thickness of the panels should be selected to ensure sufficient impact resistance in conjunction with a suitable support structure. The panels must be sufficiently secured with closely spaced screw connections. All joints must either feature tongue-and-groove connections or be covered with adhesive. Edge joints of approx. 10 mm must be kept open at the connections with adjoining construction parts. Schlüter®-DITRA-HEAT neutralise’s the stresses in the tile covering and also prevents the permeation of moisture.

Wooden floors

The direct installation of ceramic coverings over wooden floors is generally feasible, provided the floorboards have tongueand- groove connections, are sufficiently load-bearing, and are tightly screwed down. The wooden substrate should have reached a balanced moisture level prior to the installation of Schlüter®-DITRA-HEAT. Experts recommend the installation of an additional layer of plywood. Uneven floors must be levelled before the installation of other materials.

Masonry/mixed substrates

Solid masonry made of bricks, lime sand bricks, cement-bonded stones, cellular concrete or the like is generally a suitable substrate for Schlüter®-DITRA-HEAT. Uneven sections must be levelled in advance. In case of restoration projects as well as renovations and extensions, substrates frequently consist of mixed materials (mixed masonry), which are prone to cracking at the edges due to varying deformation. The installation of Schlüter®-DITRA-HEAT ensures that the resulting stresses and cracks are not transferred to the tile covering.

Plaster/ gypsum

Gypsum-based substrates should be completely dry in accordance with testing that follows the recognized regulations – surfaces may need to be pre-treated with a primer. Schlüter®-DITRA-HEAT can be installed with dry-set mortars or other suitable thin-set mortars.

Contact Schlüter-Systems Ltd

Units 3-5 Bardon 22,
Beveridge Lane, Coalville,
Leicestershire, LE67 1TE
Phone: +44 (0) 1530 813396

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