The Schluter-Ditra membrane is an uncoupling and waterproofing layer used in tile installations, primarily over plywood or concrete substrates. Its purpose is to prevent tile cracks caused by substrate movement and to mitigate potential water damage. Proper installation involves substrate preparation, mortar application, membrane embedding, and optional waterproofing measures. This article details the recommended procedures based on available documentation.
Substrate Preparation
Prior to Ditra installation, the substrate requires preparation. This often involves removing existing tile and the associated mortar. Three methods can be employed to remove the old mortar from the plywood or concrete subfloor. The documentation does not specify what these methods are. Once the old material is removed, the substrate must be primed. If the primer does not readily come off the substrate, the surface is considered ready for the next step.
Dry-Fitting and Priming
Before applying mortar, it is recommended to dry-fit the Ditra mats to the substrate. This allows for accurate cutting and placement, minimizing adjustments while working with wet mortar. Cutting the pieces to fit the space before applying mortar speeds up the installation process and prevents the mortar from drying and skinning over.
For plywood or concrete substrates, priming is a necessary step. The documentation details a process for priming, but does not specify the type of primer to use.
Mortar Application and Membrane Embedding
The application of thinset mortar is a critical step. The mortar should be mixed to a loose consistency, with sufficient water added to ensure it bonds to the fleece backing of the Ditra membrane. Insufficient water is a common error. Schluter’s All-Set mortar is recommended for all Schluter-related installations, including Ditra over wood or concrete, tile installation over Ditra, Kerdi installation for waterproofing, and Schluter shower pan installations. Using All-Set may also provide an extended warranty.
The appropriate trowel size is essential for proper mortar application. A 1/4 x 3/16 V-notch trowel or an 11/64-inch square-notch trowel (specifically designed for Ditra) can be used. When using alternative products, it is crucial to consult the manufacturer’s instructions for the correct trowel size.
Directional troweling is also important. The notches should be troweled in the short direction of the membrane. This allows air trapped in the mortar channels to escape more easily. The documentation suggests visualizing the unrolling of the membrane and troweling perpendicular to that direction.
Installing Ditra in Sections
Working with small sections of Ditra at a time is recommended. The substrate should be dampened before spreading the mortar to prevent it from drying too quickly. The goal is to achieve a saturated surface dry (SSD) condition – a damp substrate with a dry surface.
The Ditra membrane can be folded in half (without creasing) to facilitate installation in sections. One half is embedded in the mortar, then the other half is peeled back and installed similarly. This technique is useful when pieces have already been cut and positioned.
Pressure and Air Removal
Once the Ditra membrane is placed on the mortar, applying good pressure is crucial to ensure proper embedding. This can be achieved using a roller, a wood float, or a piece of 2x4 lumber. Schluter manufactures a dedicated roller for this purpose. The technique involves starting in the middle and working towards the edges, collapsing the mortar ridges and pushing out any trapped air. Regularly inspecting the transfer of thinset to the membrane by lifting a corner is also recommended. Walking over the installed Ditra surface further ensures proper embedding.
Addressing Common Issues
Several issues can arise during Ditra installation. If the membrane does not stick to the floor, potential causes include improper mortar, incorrect mortar mixing, unsuitable substrate, non-directional troweling, mortar drying too quickly, incorrect trowel size, or “memory” in the roll.
If the edges of the Ditra membrane curl up, it is likely due to “roll memory” – the membrane retaining its rolled shape.
Optional Waterproofing
While Ditra provides a degree of waterproofing, additional waterproofing is recommended, particularly around toilets. This involves applying Schluter ALL-SET mixed to a membrane consistency using a KERDI trowel. KERDI-KERECK prefab corners are then embedded in the corners and overlapped with KERDI-BAND by at least 2 inches. The corners should be flattened to avoid interference with baseboards or tile flooring. This step is intended to mitigate potential damage from overflowing toilets.
Installation Steps Summary
The installation process can be summarized as follows:
- Mix the thinset loosely.
- Dampen the floor.
- Dry-fit the Ditra pieces.
- Use the correct trowel size.
- Trowel the notches in the same direction.
- Install in small sections.
- Apply firm pressure to embed the membrane.
Considerations During Installation
During installation, it is advisable to turn off the air conditioning and block any heat registers to prevent air from blowing across the exposed thinset notches. This helps maintain the mortar’s consistency and prevents premature drying.
Peel and Stick Variation
A variation of Ditra, Ditra Peel and Stick, offers a simplified installation process. This version features a pressure-sensitive adhesive backing. The installation steps for Ditra Peel and Stick include substrate preparation, dry-fitting, priming, mat installation (starting at the toilet and working towards the doorway), and pressing the mat firmly into the substrate using a wood float in two perpendicular directions. Optional waterproofing measures, similar to those described for standard Ditra, can also be applied.
Conclusion
The Schluter-Ditra membrane is a valuable component in tile flooring installations, providing uncoupling and waterproofing benefits. Successful installation relies on careful substrate preparation, proper mortar application, thorough membrane embedding, and attention to detail. Following the outlined steps and addressing potential issues proactively will contribute to a durable and long-lasting tile floor.