TT - Application Directly on Waterproofing Membranes
Craftsman Guide / Wet Rooms Directly on Waterproofing: Application & Preparation. Guidance for drain grate installation, skim-coating with tile adhesive, and drying times on wet-room waterproofing me…
Updated
by tomas martinsson
Craftsman Guide / Wet Rooms
Directly on Waterproofing: Application & Preparation
Guidance for drain grate installation, skim-coating with tile adhesive, and drying times on wet-room waterproofing membranes.
ℹ️ About This Guide: This guide does not cover the installation of the waterproofing membrane itself, but focuses on how substrate preparation is carried out once an approved waterproofing system is fully installed.
⚠️ Recommended Waterproofing Systems & Execution:
We recommend Kiilto or Zebra as they explicitly approve our systems. Contact us for training in these systems. Zebra provides comprehensive installation instructions and quality documentation for tiling and microcement.
Applying microcement over waterproofing membranes takes longer than traditional tiling. In terms of cost, however, it usually aligns closely with large-format tiles due to the higher material and handling expenses associated with large slabs.
Applying microcement over waterproofing membranes takes longer than traditional tiling. In terms of cost, however, it usually aligns closely with large-format tiles due to the higher material and handling expenses associated with large slabs.
1. Installation & Bonding of Drain Grates
Bond the grate frame to the waterproofing membrane using an approved moisture-curing adhesive (such as Tec7 or as specified by the manufacturer). (Note: Zebra requires a Purus grate for microcement).
🛡️ Workflow & Moisture Protection for FLOORS ONLY:
• Recommended System: We primarily recommend Forcrete for bathroom floors.
• Order of Work: Typically, the floor is always completed before the walls to prevent water from running behind tiles and into the adhesive bed. If the walls are already finished and the floor is done afterward, the grate must be set in tile adhesive.
• Moisture Barrier with Primapox: If using Topciment in this scenario, the adhesive bed must be primed and moisture-blocked with Primapox 100 Barrier prior to troweling the microcement. The epoxy prevents water from migrating underneath between the grate and membrane, which otherwise draws in moisture and causes permanent dark staining in the cement.
• Recommended System: We primarily recommend Forcrete for bathroom floors.
• Order of Work: Typically, the floor is always completed before the walls to prevent water from running behind tiles and into the adhesive bed. If the walls are already finished and the floor is done afterward, the grate must be set in tile adhesive.
• Moisture Barrier with Primapox: If using Topciment in this scenario, the adhesive bed must be primed and moisture-blocked with Primapox 100 Barrier prior to troweling the microcement. The epoxy prevents water from migrating underneath between the grate and membrane, which otherwise draws in moisture and causes permanent dark staining in the cement.
2. Application of Moisture-Resistant Tile Adhesive
Apply the specific tile adhesive prescribed by the waterproofing manufacturer. This step is critical for system warranties. A completely flat and uniform application is required—depressions in the adhesive will lead to standing water puddles and discoloration.
• On Walls: The adhesive is applied to secure bonding to the membrane and to flush out the overlap seams of the waterproofing sheet. Because microcement builds only 2–3 mm, sheet edges will otherwise telegraph through the finish.
• On Floors: Trowel the adhesive flush with the flange of the drain grate (e.g., 4 mm for mosaic grates, 6 mm for standard grates). Using a dedicated microcement grate with only 3 mm build height is recommended to minimize adhesive thickness.
• On Floors: Trowel the adhesive flush with the flange of the drain grate (e.g., 4 mm for mosaic grates, 6 mm for standard grates). Using a dedicated microcement grate with only 3 mm build height is recommended to minimize adhesive thickness.
🛑 Thicker Adhesive Beds & Linear / Wall Drains:
Linear wall drains often require a thicker layer of adhesive, significantly extending drying times.
• Increase Fall in Advance: Increase the slope slightly in the shower area during initial self-leveling to avoid building thick adhesive layers outside the shower zone.
• Reinforcement: When building thicker layers, embedding reinforcement mesh (160 g mesh) into the adhesive is recommended. Always consult your waterproofing supplier.
Linear wall drains often require a thicker layer of adhesive, significantly extending drying times.
• Increase Fall in Advance: Increase the slope slightly in the shower area during initial self-leveling to avoid building thick adhesive layers outside the shower zone.
• Reinforcement: When building thicker layers, embedding reinforcement mesh (160 g mesh) into the adhesive is recommended. Always consult your waterproofing supplier.
3. Techniques for Flat Skim-Coating
To achieve a completely uniform level, you can comb out material with a notched trowel everywhere except directly across the membrane overlap seams:
• Once the combed adhesive sets, fill in the ridges using a smooth trowel.
• On floors, choose a notch size that matches the build height of the drain grate.
• Skim the surface smooth an additional time if necessary so no ridges or texture remain.
• Crack Inspection: If any cracks develop in the adhesive before microcement is applied, they must be fully addressed in consultation with the manufacturer.
4. Priming and Drying Times
Once the tile adhesive is fully dry through, prime the surface with Primacem ABS or Acricem Resin.
Cure-Through Requirement:
Ensure the adhesive is 100% dry through. Trapped moisture within the substrate causes tension and shrinkage cracks that will propagate up into the microcement.
Always Use Rapid-Setting Adhesive: Always use rapid-setting adhesive when leveling floor surfaces. Standard adhesive takes too long to cure fully in thick layers, increasing the risk of subsequent settlement cracks.
Always Use Rapid-Setting Adhesive: Always use rapid-setting adhesive when leveling floor surfaces. Standard adhesive takes too long to cure fully in thick layers, increasing the risk of subsequent settlement cracks.
Next Steps: Application in Bathrooms
Once the adhesive has dried and is primed, proceed to reinforcement mesh and microcement application:
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