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Schlüter®-DITRA 25

Substrates for Schlüter®-DITRA 25

Substrates on which Schlüter®-DITRA 25 is to be installed must always be checked for their suitability 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. Any unevenness or height and slope differences in the substrate must be levelled prior to the application of Schlüter®-DITRA 25.

Concrete
Concrete is subject to lengthy deformation processes due to shrinkage. Concrete and pre-stressed concrete may build up tension because of deflection. Thanks to the installation of Schlüter®-DITRA 25, the tensions occurring (in the floor and wall area) between the concrete and the tile covering are absorbed.

Mortar screeds
With Schlüter®-DITRA 25, tiles can be installed on green cementitious screeds as soon as they are ready to bear weight. According to the applicable standards, mortar screeds must cure a minimum of 28 days prior to the installation of tile and their residual moisture content must be below 2% (percentage by volume). In particular, floating screeds and heated screeds tend to change shape or develop cracks after installation, e.g. due to load stresses or temperature changes.
Schlüter®-DITRA 25 absorbs inherent stresses between the concrete and tile covering so that the tile can be installed as soon as the concrete is hard enough to be walked upon, (depth of screed does need to be considered and additional drying time should be allowed in some instances, please contact us for advice).
Cracks and curling forming in the screed over time will be neutralised by DITRA 25 and will not be transferred to the tile covering.

Gypsum based screeds
According to the applicable standards, the residual moisture of gypsum based screeds should not exceed 0.5% (percentage by volume) prior to the installation of tiles. With the application of Schlüter®-DITRA 25, tile coverings can be installed as soon as the residual moisture is below 2.0% (percentage by volume).
If required, the screed surface may need to be pre treated (sanding, priming) in accordance with the applicable industry standards and manufacturers’ recommendations.
Schlüter®-DITRA 25 can be applied using thin-bed tile adhesives that are suitable for the substrate. Schlüter®-DITRA 25 protects the screed against moisture penetration from the surface. Gypsum based screeds are sensitive to moisture and must be protected from additional moisture penetration, especially on the underside.

Radiant heated screeds
Schlüter®-DITRA 25 may be used over heated screeds as described in the sections on mortar screeds and gypsum based screeds. With Schlüter®-DITRA 25, tiles can be heated seven days after installation.
Starting at 77 ºF (25 ºC), the radiant heated floor temperature can be raised gradually by +9 °F (+5 °C) per day, to a maximum of 104 ºF (40 ºC). The air channels of Schlüter®- DITRA 25 allow for a quick and even distribution of heat below the tile covering.
Note: For radiant heated floors, we recommend our system Schlüter®-BEKOTEC-THERM, the ceramic thermal comfort floor.
Schlüter®-DITRA 25 is also recommended for uncoupling of radiant heated floors consisting of thin electric heating mats. Schlüter®-DITRA 25 may be installed either above or below the heating mat. However, the uncoupling function is more effective if Schlüter®-DITRA 25 is installed above the heating mat.
Schlüter®-DITRA-HEAT is a special uncoupling membrane that was developed for attachment of the matching system heating cables of electrical floor/wall heating systems. Further information can be found in product data sheet 6.4.

Dry screed elements
Following the professional installation of the dry screed material according to manufacturer instructions, the maximum tile size can be freely chosen with the use of Schlüter®- DITRA 25.

Masonry / mixed Substrates
Masonry consisting of brick, stone, limestone, cement block, lightweight concrete, or similar is generally a suitable substrate for Schlüter®-DITRA 25. Uneven areas must be levelled in advance. Particularly in refurbishments or extensions, different materials (mixed masonry) may be encountered. At the transitions, movement can cause cracks. With Schlüter®-DITRA 25, stresses and cracks do not transfer to the tile covering.

Stucco / plaster
Plaster substrates should be examined in accordance with the applicable building codes to ensure they are dry. The surface may need to be pre-treated with a primer. Schlüter®-DITRA 25 can be applied using thin-bed tile adhesives that are suitable for the substrate.

Balconies / terraces
As an uncoupling membrane, Schlüter®-DITRA 25 neutralises the stresses between the substrate and the tile covering that are caused by the frequent and extensive temperature changes occurring on balconies. Moreover, Schlüter®-DITRA 25 can serve as the sole waterproofing membrane in tile assemblies for cantilevered balconies and terraces that are built directly on the ground (note instructions for waterproofing). The substrate (concrete, screed) must be sufficiently sloped.
For refurbishments, the existing surface assembly can generally remain, provided it is sufficiently sloped and load bearing. Prior to the application of Schlüter®-DITRA 25 over existing and cracked tile floors, the loose tiles must be removed and the remaining cavities filled using an appropriate adhesive. The preparations also include ensuring a proper slope in the substrate.
We recommend Schlüter®-DITRA-DRAIN (see product data sheet 6.2) for coverings with side lengths exceeding 30 x 30 cm.

Rooftop terraces
In the case of roof terraces over residential/ commercial or other spaces as well as roof-covered surfaces, the surface needs to be designed as a flat roof, following the applicable technical rules for roof structures. In the case of heat-insulated residential and commercial spaces (as well as spaces with expected temperature differences from the outside), a vapor barrier as well as ceiling insulation is required in a standard-confirming assembly. National standards and/or the applicable technical data sheets need to be observed if applicable.
A drainage system such as Schlüter®-TROBA or Schlüter®-TROBA-PLUS must be installed over this top insulation layer. This is then topped with screed to act as a load distribution layer. Schlüter®-DITRA 25 is installed over this screed as an uncoupling layer with the tile covering and as a moisture barrier for the screed. Otherwise, any loose or insufficiently attached parts must be removed and defects and missing sloping leveled with a suitable suitable self-levelling compound prior to adhering Schlüter®-DITRA 25.
We recommend Schlüter®-DITRA-DRAIN (see product data sheet 6.2) for coverings with side lengths exceeding 30 x 30 cm.

Synthetic flooring and surface coatings
In principle, the surface must be load bearing and prepared in such a way that a suitable tile adhesive will adhere to it and anchor the fleece on the underside of the Schlüter®-DITRA 25 matting. The compatibility of the adhesive for the substrate and Schlüter®-DITRA 25 must be verified ahead of time.

Plywood and chipboard
These materials are particularly prone to deformation under the influence of moisture (or significant changes in atmospheric humidity). The plywood and chipboard panels used in construction should therefore be exterior grade. In principle, plywood can be used as backing materials for Schlüter®-DITRA 25 on both floors and walls in interior applications. The thickness of the panels must be sufficient to ensure stability in conjunction with a suitable supporting construction. Attach the panels with screws set at the required minimum spacing. The joints must feature tongue and groove connections and should be secured with additional adhesive.
Movement joints of at least 10 mm must be left at the transition to other construction parts. Schlüter®-DITRA 25 neutralises the stress occurring in the tile covering and prevents the penetration of moisture.

Structural plank subflooring
Sufficiently load bearing structural plank subflooring in tongue and groove construction, with the appropriate screws in place, is suited in principle as a substrate for ceramic tiles. The timber substrate should have reached the equilibrium moisture content prior to installing Schlüter®-DITRA 25. However, an additional layer of plywood panels is recommended. Uneven floors must be levelled using an appropriate levelling compound.

Bituminous screed (paving grade asphalt)
Schlüter®-DITRA 25 allows for the installation of ceramic coverings on standard weightbearing, unheated mastic asphalt screeds in indoor areas. The surface needs to be sanded or must be suitable to allow for the proper adhesion of the thin-bed tile adhesive for the installation of Schlüter®-DITRA 25.


Contact Schlüter-Systems Ltd

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

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