Schlüter®-DITRA 25 | Schlüter-Systems
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Schlüter®-DITRA 25

Application and Function

Schlüter-DITRA 25 is a polyethylene membrane with a grid structure of square cavities, each cut back in a dovetail configuration and an anchoring fleece laminated to its underside. Designed for tile and natural stone installations, Schlüter-DITRA 25 serves as a waterproofing membrane, a vapour pressure equalisation layer to accommodate construction moisture occurring within the substrate and an uncoupling layer for problematic substrates.

The substrate must be even and load bearing. To bond Schlüter-DITRA 25, use a bonding adhesive that is appropriate for the substrate. Apply the adhesive using a 3 x 3 mm or 4 x 4 mm notched trowel. The anchoring fleece on the underside of Schlüter-DITRA 25 must be fully engaged in the adhesive to provide a mechanical bond to the substrate. Please observe the open time of the bonding adhesive.

Using the thin-bed method and following all applicable industry standards, set the tile or stone covering directly on the Schlüter-DITRA 25 in such a way that the tile adhesive becomes mechanically anchored in the square, cut back cavities of the Schlüter-DITRA 25 matting. 


Summary of functions

a) Uncoupling
Schlüter-DITRA 25 uncouples the floor covering from the substrate and neutralises the tensions between the substrate and the tile covering that result from the varying deformations of the materials. Likewise, stress cracks in the substrate are bridged and are, therefore, not transferred to the surface covering. 

b) Waterproofing
Schlüter-DITRA  25 is a waterproof polyethylene membrane with a relatively high vapour diffusion density. Provided the mat joints and the connections to walls and built-in elements are properly installed, Schlüter-DITRA 25 can be used to create a certified bonded waterproofing assembly with the tile covering. Schlüter-DITRA 25 can be installed in accordance with the German waterproofing standards 18531-5* as well as 18534. Water exposure classes: W0-I to W3-I*. Furthermore, Schlüter-DITRA 25 features the national technical approval (abP) required in Germany. 

Moisture load class according to ZDB: 0 to B0, as well as A and C.

Schlüter-DITRA 25 has the required European Technical Assessment (ETA) as specified in ETAG 022 (bonded waterproofing assemblies) and bears CE marking.

Exclusively use system-approved thin-bed adhesives for areas that require CE conformity or compliance with the general certificate of national technical approval (abP). Please contact us at the address shown in this data sheet for further information about suitable thin-bed adhesives and the corresponding test certificates.

Therefore, Schlüter-DITRA 25 protects the substrate against damage due to moisture penetration and aggressive substances.

c) Equalisation of vapour pressure
The interconnected air channels between the cavities on the underside of the Schlüter-DITRA 25 matting remain open. This allows moisture in the substrate to evaporate, therefore neutralising vapour pressure.

d) Load distribution (load impact)
Tiles that are installed in floor coverings with Schlüter-DITRA 25 should have a minimum size of 5 x 5 cm and be at least 5.5 mm thick. The bottom of the square cavities in Schlüter-DITRA  25, which are filled with thin-bed adhesive, directly transfer the load impact on the tile covering to the substrate. As a consequence, tile coverings installed on top of Schlüter-DITRA  25 are highly load resistant. If high traffic loads are expected (e.g. in commercial areas) or if the floor must accommodate large point loads (such as concert pianos, fork lifts, shelf systems), the selected tiles must have adequate thickness and pressure stability for the corresponding application area.

The requirements of the mandatory guideline “Ceramic Floor Coverings With High Impact Resistance,” published by the German Construction Industry Association (ZDB) must be followed.

In areas with high impact loads, the tiles must be fully embedded in the thin-bed adhesive. The contact surface of Schlüter-DITRA 25 amounts to approximately 50% of the total surface. This can reduce the load bearing capacity in case of point loads. For high point loads, select a tile thickness that is capable of distributing the loads. Ceramic tile coverings should not be exposed to the direct impact of hard objects. 

e) Adhesive properties
Due to the bond of the fleece fabric with the adhesive over the substrate and the mechanical anchoring of the adhesive. in the cut-back indentations, Schlüter-DITRA 25 creates a lasting bond between the tile covering and the substrate. Consequently, Schlüter-DITRA 25 can be used for wall and floor coverings. Anchor plugs may be used with wall coverings if necessary. 


Schlüter®-DITRA 25

Installation

1.The substrate must be free of bond inhibiting components, be load bearing and even. Any unevenness in the substrate must be levelled prior to the application of Schlüter-DITRA 25.

2.The adhesive used for bonding Schlüter-DITRA 25 must be selected to suit the substrate type. The adhesive must bond well with the substrate and mechanically set in the anchoring fleece of Schlüter-DITRA 25. Standard C2 adhesives are suitable for most substrates. It is therefore advantageous to prepare the adhesive in-line with manufacturers recommendations. Check for any incompatibilities of materials. If using covering materials with a lateral length ≥ 30 cm, we recommend bonding the covering material to DITRA 25 using a water-binding tile adhesive for rapid curing and drying.

3.Apply thin-bed mortar on the substrate with a notched trowel (recommended size: 3 x 3 mm or 4 x 4 mm; mortar requirement approx. 1.5 kg/m²).

4.Individual courses of Schlüter-DITRA 25 are cut to size. Solidly embed the anchoring fleece on the underside of Schlüter-DITRA 25 in the adhesive so that its entire surface is bonded and immediately work it into the adhesive using a float or screed trowel. Among other tools, an orbital sander is well-suited for this purpose. Please observe the open time of the bonding adhesive. When initially positioning Schlüter-DITRA 25, it is advisable to align and position the matting while slightly stretching it. This is best done with an additional helper. Tightly abut the individual membranes.

 


Schlüter®-DITRA 25

Material

Schlüter-DITRA 25 is a polyethylene sheet with a grid structure of square cavities, each cut back in a dovetail configuration. An anchoring fleece is laminated to the underside. The rib height is approximately 3 mm. Polyethylene is not permanently UV stable. Prolonged exposure to intensive sunlight should be avoided when storing the material. 


Material properties and areas of application

Schlüter-DITRA 25 is flexible, bridges cracks and will not rot. In addition, it is highly resistant to watery solutions, salts, acids and alkalis, as well as many organic solvents, alcohols and oils.

Its resistance to specific stresses must be examined separately on the basis of the expected concentration, temperature and exposure time. The vapour diffusion density is relatively high. The material is physiologically safe.

Schlüter-DITRA 25 is used with a great variety of applications. Its suitability for specific chemical or mechanical conditions must be evaluated for each individual case. The instructions below provide some general guidelines.

Coverings constructed with Schlüter DITRA 25 may have a certain hollow sound when they are walked upon with hard shoes or tapped with a hard object.


Schlüter®-DITRA 25

Waterproofing with Schlüter®-DITRA 25

Provided the mat joints and the connections to built-in elements and upright structural fixtures are carefully sealed, Schlüter-DITRA 25 can be used to create a certified bonded waterproofing assembly with the tile covering. Schlüter-DITRA 25 can be installed in accordance with the German waterproofing standards 18531-5 as well as 18534. Water exposure classes: W0-I to W3-I. Furthermore, Schlüter-DITRA 25 features the national technical approval (abP) required in Germany.

Moisture load class according to ZDB: 0 to B0, as well as A and C.

Schlüter-DITRA 25 has the required European Technical Assessment (ETA) as specified in ETAG 022 (bonded waterproofing assemblies) and bears CE marking. Exclusively use system-approved thin-bed adhesive for areas that require CE conformity or compliance with the general certificate of national technical approval (abP). Please contact us at the address shown in this data sheet for further information about suitable thin-bed adhesive and the corresponding test certificates.

We recommend the use of our waterproofing membrane Schlüter-KERDI (see product data sheet 8.1 Schlüter-KERDI) for applications of Utilisation Class B, “pools.” Schlüter-DITRA 25 therefore protects the substrate from damages due to the penetration of moisture and aggressive substances.

The abutting joints are covered with the sealing adhesive Schlüter-KERDI-COLL-L and Schlüter-KERDI-KEBA (minimum width: 12.5 cm) is solidly embedded over the joint. For floor to wall transitions, adhere the Schlüter-KERDI-KEBA in the appropriate width. The sealing band should overlap at least 5 cm.

Schlüter-KERDI-KEBA is also suited for sealing joints with existing fixtures such as door frames, window frames and balcony edge profiles of metal, wood or plastic. Start by applying Schlüter-KERDI-FIX to the part of the fixture that is to be adhered. The remaining width is fully embedded on Schlüter-DITRA  25, using the adhesive Schlüter-KERDI-COLL-L.

The suitability of Schlüter-KERDI-FIX for the material of the corresponding fixtures must be verified beforehand.

Cut Schlüter-DITRA 25 above structural and seismic expansion joints, then cover the joint with Schlüter-KERDI-FLEX.

Schlüter-KERDI-FLEX can also be used for flexible finishing edges. Alternatively, Schlüter-KERDI-KEBA may be used, provided a loose fold is left above the joint.

Note regarding floor drains:

Schlüter-KERDI-DRAIN and Schlüter-KERDI-LINE are components that were specifically developed for connection to bonded waterproofing assemblies. Schlüter-DITRA 25 can be quickly and reliably abutted in these cases with the use of Schlüter-KERDI collars.


Schlüter®-DITRA 25


Schlüter®-DITRA


Schlüter®-DITRA 25

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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, lime - stone, 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 levelled 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.


Schlüter®-DITRA 25


Schlüter®-DITRA 25

Frequently asked questions

Heated screed

What are the work steps for heating up an in-floor heating system for the first time?

Show answer

The uncoupling membranes Schlüter®-DITRA 25 and Schlüter®-DITRA-DRAIN make it possible to install the mats and tiles on unheated screed. Seven days after the completion of the covering assembly, the screed should then be heated to the required operating temperature in steps of 5°K per day.

The system does not require any conventional functional heating for interface coordination.  Our ceramic thermal comfort floor Schlüter®-BEKOTEC-THERM is a complete system for the construction of heated floors.

Seaming tapes

Is it necessary to use seaming tapes for Schlüter®-DITRA 25 in areas without exposure to moisture?

Show answer

No, seaming tapes are not required in areas without exposure to moisture. One exception may be the installation of moisture-sensitive natural stone on green substrates. In this case, seaming tapes would be used with Schlüter®-DITRA 25 to prevent any moisture from the screed to permeate the natural stone.

Expansion joints

Can I cover expansion joints from the substrate with Schlüter®-DITRA 25 or Schlüter®-DITRA-DRAIN?

Show answer

No, expansion joints from the substrate always have to be continued.

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