Discussion of thin-set mortars and Schluter-DITRA installations
Question: Can ceramic tile, including porcelain tile, be set on Schluter-DITRA 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 Schluter-DITRA 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 Schluter-DITRA 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 Schluter-DITRA and ceramic tile, including porcelain tile, drying takes place very slowly through the open joints in the tile covering. [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.
15 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 Schluter-DITRA in both interior and exterior applications. See relevant testing data for more details.
Remember, the type of mortar used to apply Schluter-DITRA depends on the type of substrate. The mortar must bond to the substrate and mechanically anchor the fleece on the underside of the DITRA. For example, bonding DITRA to wood requires latex-modified thin-set mortar. Additionally, all mortars (modified and unmodified) have an acceptable temperature range that must be observed during application and curing.
Relevant information to tile floor installation.Ditra Installation Instructions
Guidelines for the Placement of Movement Joints