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Schluter®-DITRA

FAQ

expand Q. Why should I use Schluter-DITRA in my tile installation?

A. Ceramic and stone tiles are durable, easy to maintain, and hygienic, representing the ideal surface coverings.  However, today’s lightweight construction methods can make the installation of hard surface coverings particularly challenging. In order to protect the integrity of the tile assembly, an underlayment that performs multiple functions is required.  Schluter-DITRA is specifically designed to allow the installation of ceramic and stone tile over any even and load-bearing substrate. The integration of DITRA’s uncoupling, waterproofing, load-distribution, and vapor management functions makes consistent results viable.

Tile has been successfully installed for thousands of years by incorporating an uncoupling layer, or forgiving shear interface, within the tile assembly. Schluter-DITRA provides uncoupling through its open rib structure, which allows for in-plane movement that effectively neutralizes the differential movement stresses between the substrate and the tile, thus eliminating the major cause of cracking and delaminating of the tiled surface.

Schluter-DITRA provides reliable waterproofing in interior and exterior applications.  Its polyethylene composition protects the substrate from moisture penetration, which is particularly important in today’s building environment where most substrates are moisture sensitive.

The distinguishing feature of Schluter-DITRA is the existence of free space created by the configured channels on the underside of the matting.  The free space provides an escape route for excess moisture and vapor that could otherwise cause damage to the tile layer above. Thus, DITRA effectively manages moisture beneath the tile covering.

When placed on a solid foundation, columns or pillars can support tremendous loads. The same physical principle applies to Schluter-DITRA installations.  Column-like mortar structures are formed in the cutback cavities of the matting.  Loads are transferred from the tile covering through these column-like mortar structures to the substrate.  Since DITRA is virtually incompressible within the tile assembly, the advantages of uncoupling are achieved without sacrificing point load distribution capabilities.  The ability of DITRA installations to support and distribute heavy loads while preserving the integrity of the tiled surface has been verified through extensive laboratory and field testing, including applications exposed to vehicular traffic.


expand Q. I’m planning to install my tile using Schluter-DITRA. Where do I begin?

A. The first thing to do is plan out the installation according to the Schluter-DITRA Installation Handbook.  The Handbook is available on our website for download or you can call Customer Support to request a print copy.  The comprehensive Handbook features all the warranted Schluter-DITRA details for ceramic and stone tile installation in both interior and exterior applications over various substrates, such as plywood, OSB, concrete, poured gypsum underlayments, and heated floors.  Each application features a detailed illustration and provides direction on substrate preparation, appropriate setting and grouting materials, movement joints, etc.


expand Q. What size trowel should I use to install Schluter-DITRA?

A. A 1/4" x 3/16" or 5/16" x 5/16" V-notched trowel is recommended.  Mix your thin-set mortar to a fairly fluid consistency (but still able to hold a notch) and solidly embed the Schluter-DITRA into the fresh mortar with a float or screed trowel.  It is good practice to periodically lift a corner of the DITRA after embedding it in the thin-set mortar to check the fleece for full coverage.


expand Q. What type of thin-set mortar should I use when installing Schluter-DITRA?

A. The type of thin-set mortar used to install Schluter-DITRA depends on the substrate material.  For example, to set DITRA over plywood or OSB, a modified thin-set mortar meeting the requirements of ANSI A118.11 is used.  To set DITRA over concrete or gypsum, Schluter-Systems recommends an unmodified thin-set mortar meeting the requirements of ANSI A118.1.  Please consult the Schluter-DITRA Installation Handbook before beginning your tile project to confirm the proper materials selection.


expand Q. What type of thin-set mortar should I use when setting tile over Schluter-DITRA?

A. Schluter-Systems requires the use of an unmodified thin-set mortar meeting the requirements of ANSI A118.1 to install ceramic (including porcelain) and stone tile over Schluter-DITRA*.

We don’t recommend the use of modified thin-set mortars to set tile over DITRA because these mortars must air dry to cure properly.  When sandwiched between two impervious layers such as DITRA and porcelain tile, drying takes place very slowly through the open grout joints.  [According to the TCA Handbook for Ceramic Tile Installation, this drying period can fluctuate from 14 days to over 60 days, depending on the geographic location, the climatic conditions, and whether the installation is interior or exterior].  Therefore, extended cure times would be required before grouting if using modified thin-set mortars between DITRA and ceramic tile, including porcelain tile. If extended cure times were not observed, the results could be unpredictable.  This is even more important to consider in exterior applications that are exposed to rain, as there is the additional concern of latex leaching.

*Exception:  Certain moisture-sensitive stones, e.g., green marble, or resin-backed tiles may require special setting materials.  Please consult your stone supplier and Schluter-Systems for more information.  For an acid-resistant covering, use an epoxy adhesive to set and grout the tile.


expand Q. How do I know if the thin-set mortar is modified or unmodified?

A. In general, unmodified thin-set mortar is a blend of Portland cement, sand, and water retention agents that is mixed with water by the user.  The appropriate product standard for unmodified thin-set mortars is ANSI A118.1.  Look for this standard on the packaging (e.g., product meets ANSI A118.1 when mixed with water).  Unmodified thin-set mortar may also be referred to as dry-set mortar by the manufacturer.

Modified thin-set mortars are similar to unmodified thin-set mortars, but include additional polymers such as latex.  The additional polymers are introduced in either liquid or powder form.  In the first case, the user mixes an unmodified or dry-set mortar powder with a liquid polymer additive instead of water.  In the second case, the polymers are added by the manufacturer to the dry blend in powder form.  The user then mixes the powder with water.  The appropriate product standards for modified thin-set mortars include ANSI A118.4 and ANSI A118.11.


expand Q. Can I use a premixed thin-set mortar to install Schluter-DITRA and tile?

A. No.  Schluter-Systems does not recommend the use of premixed thin-set mortars (mastics/adhesives) in any Schluter-DITRA installation.


expand Q. Do I need to provide movement joints when I use Schluter-DITRA in my tile installation?

A. Yes.  Schluter-DITRA does not eliminate the need for movement joints.  Movement joints are essential in any tile installation to prevent the development of stress in the tile layer due to changes in temperature, moisture, and loading.  These include perimeter joints at field edges and restraining surfaces, and surface joints within the tile field at regular intervals.  Please refer to the Schluter-DITRA Installation Handbook for further discussion and guidelines for movement joint placement.

Note:  Schluter-Systems’ prefabricated movement joint profiles protect tile edges and prevent sound bridges and surface water penetration, resulting in a permanent, maintenance-free installation.  The family of Schluter-DILEX prefabricated movement profiles includes a variety of shapes, sizes, and materials to suit different applications.


expand Q. Can I install glass tile over Schluter-DITRA?

A. Schluter-Systems does not recommend the use of glass tile over Schluter-DITRA.


expand Q. I tried to snap chalk lines on Schluter-DITRA before setting my tile, but the chalk rubs off the plastic easily while I am working. What can I do?

A. One option is to apply hair spray over the chalk lines.  You don’t have to worry about the hair spray acting as a bond breaker because the thin-set mortar applied over Schluter-DITRA is locked into the cut-back cavities on top of the membrane.  Another option is to use an ink line instead of a chalk line.


expand Q. I need to remove and reinstall a tile on Schluter-DITRA. How can I do this safely?

A. If you are in the process of setting the tile and the thin-set mortar is still fresh, simply run your margin trowel under the surface of the tile to break the suction created by the thin-set mortar and remove the tile.  If you have already set the tile and the thin-set mortar has cured, you will need to take a different approach.  Cut through the tile assembly down to the substrate around the tile to be replaced.  Remove tile, DITRA, and thin-set mortar from the substrate, taking care not to disrupt adjacent tile work.  Reinstall a new section of DITRA and tile using the appropriate setting materials per the Schluter-DITRA Installation Handbook.