Installation Guide

QUESTION: Can ceramic tile, including porcelain tile, be set on DITRA-HEAT with unmodified thin-set mortar?
ANSWER: YES. In fact, we recommend it. Here’s why:
Portland cement-based unmodified thin-set mortars are dependent on the presence of moisture for hydration in order to gain strength. Since
DITRA-HEAT is impervious, it does not deprive the mortar of its moisture. This allows the cement to properly hydrate, resulting in a strong,
dense bond coat. In fact, after the mortar has reached final set (usually within 24 hours), unmodified thin-set mortars achieve higher strengths
when cured in continually moist conditions.
QUESTION: Can ceramic tile, including porcelain tile, be set on DITRA-HEAT with latex-modified thin-set mortar?
ANSWER: In general, we DON'T recommend it. Here’s why:
Latex-modified mortars must dry for the polymers to coalesce and form a hard film in order to gain strength. When sandwiched between two
impervious materials such as DITRA-HEAT and ceramic tile, including porcelain tile, drying takes place very slowly through the open joints in
the tile covering. [According to the TCNA Handbook for Ceramic, Glass, and Stone Tile Installation, this drying period can fluctuate from 14
days to over 60 days, depending on the geographic location, the climatic conditions, etc.]. Therefore, extended cure times could be required
before grouting if using modified thin-set mortars between DITRA-HEAT and ceramic tile, including porcelain tile. If extended cure times were
not observed, the results could be unpredictable.
QUESTION: Can Schluter ALL-SET
®
and Schluter FAST-SET
®
modified thin-set mortars be used to set tile over Schluter boards
and membranes?
ANSWER: Yes.
All Schluter
®
thin-set mortars, including the Schluter ALL-SET
®
and Schluter FAST-SET
®
modified varieties can be used to set tile over DITRA,
DITRA-HEAT, KERDI, KERDI-BOARD, etc. non absorptive substrates.
QUESTION: How is this possible?
ANSWER: The key is predictability.
Schluter Systems’ modified thin-set mortars have been specifically formulated to set and gain strength in a timeframe that fits typical
installation practice, even when sandwiched between Schluter
®
membranes or boards and porcelain tile. The proportions of cement, water-
retention agents, polymers, and other components in the mixtures were balanced to ensure that extended dry times are not required. This
was validated through both laboratory and practical testing. Now, the installer can select from either unmodified or modified thin-set mortar
to install tiles within our systems according to his or her preference.
QUESTION: Why did Schluter Systems change its position on thin-set mortar?
ANSWER: We haven’t changed our position on thin-set mortar use within our systems.
Developing our own setting materials has given us the ability to guarantee consistently positive results. And since we control the formulas,
we can be sure no changes will be made that have a negative impact on setting times and strength gain in these environments.
QUESTION: Does this mean I can use other manufacturers’ modified thin-set mortars to install tile over Schluter boards and
membranes?
ANSWER: No.
Our position on thin-set mortar use within our systems in general has not changed. We have no control over the formulation of other
manufacturers’ products and therefore cannot guarantee consistently positive results with their modified thin-set mortars.
QUESTION: Can I still use other manufacturers’ unmodified thin-set mortars to install tile over Schluter boards and membranes?
ANSWER: Yes.
We still warrant the use of unmodified thin-set mortar meeting ANSI A118.1 to install tile within our systems because we have confidence in
the performance of this product category. This is based on the science of cement hydration and years of positive testing and field experience.
Please note, if Schluter
®
thin-set mortars are used with Schluter membranes an extended system warranty is available.
ADDITIONAL NOTES
Pre-mixed thin-set mortars and mastics are not suitable for use in conjuction with DITRA-HEAT and DITRA-HEAT-DUO.
Remember, the type of mortar used to apply DITRA-HEAT depends on the type of substrate. The mortar must bond to the substrate and
mechanically anchor the fleece on the underside of the DITRA-HEAT. For example, bonding DITRA-HEAT to wood requires latex-modified thin-
set mortar. When bonding DITRA-HEAT to particularly dry, porous concrete with unmodified thin-set mortar, the slab should be moistened to
saturate the concrete and help prevent premature drying of the mortar. Excess or standing surface water must be removed prior to installation.
Additionally, all mortars (modified and unmodified) have an acceptable temperature range that must be observed during application and curing.
Discussion of thin-set mortars and Schluter
®
-DITRA-HEAT installations
THIN-SET FACTS
THIN-SET FACTS 25
Schluter
®
-Systems offers thin-set mortars designed for use with Schluter
®
membranes and boards. All Schluter
®
-Systems’ thin-set mortars,
including the Schluter ALL-SET
®
and Schluter FAST-SET
®
modified varieties, can be used to set tile over Schluter
®
-DITRA, DITRA-HEAT,
KERDI, KERDI-BOARD non absorptive substrates. If Schluter
®
thin-set mortars are not used, we require unmodified thin-set mortar when
setting ceramic or porcelain tile over DITRA-HEAT.