Schluter DHERS/BW Installation Guide download pdf (Page 21)

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: We DON'T recommend it. Here’s why:

Latex-modiﬁed mortars must air 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 would

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.

ADDITIONAL NOTES

25 years of ﬁeld experience and testing by the Tile Council of North America (TCNA) support the efﬁcacy of using unmodiﬁed thin-set

mortars to bond ceramic tile, including porcelain tile, to uncoupling membranes.

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 21

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Schluter DHERS/BW Installation Guide Page 21