Gripset P39

Gripset P39 is a fibre-enhanced polyurethane-hybrid waterproofing membrane for exposed or under-tile applications. It is highly flexible, UV and weather resistant, handles early ponding and permanently wet conditions after cure, and can serve as a light-foot-trafficable finish on suitable external areas.

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How it works

P39 Membrane combines hybrid polyurethane chemistry with fibre reinforcement to achieve high elasticity and a low vapour transmission rate. This formulation prevents water absorption in constantly wet environments, such as laundries, bathrooms, podiums, and parapets. The cured film withstands light foot traffic and resists UV degradation on exposed external surfaces, or it can serve as an under-tile membrane beneath polymer-modified cement adhesives.

Numbers that matter

• >300% Class III elongation: Accommodates thermal movement and structural shifting in aerated concrete blocks, balconies, and joint transitions without cracking.
• >3MPa tensile strength: Provides high tear resistance under light foot traffic and overlaid screeds or toppings.
• 1.6g/m² / 24 hours vapour transmission: Restricts moisture vapour movement through the subfloor to protect internal spaces from rising damp.
• 1.0mm minimum dry film thickness (DFT): The required specification for under-tile applications, achieved by applying a minimum of two coats at 1.5 litres/m² total coverage.
• 1.2mm minimum dry film thickness (DFT): The required specification for exposed, trafficable roofs, achieved by applying three coats at 2.0 litres/m² total coverage.
• 2 to 4 hour recoat window: Allows multi-coat application to proceed quickly under standard conditions (23°C and 50% relative humidity).

Where to use it

P39 Membrane bonds to common building substrates, provided they are primed correctly. Approved substrates include:

• Concrete, render, and masonry (concrete must cure for 28 days; sand-cement screeds for 7 days)
• Fibre cement sheeting and plasterboard
• Wet area timber sheeting and external grade plywood
• Aerated concrete panels and blocks

Required priming

The membrane must be applied onto primed surfaces. Select the primer based on substrate conditions:

• Porous or absorbent surfaces: Apply Gripset GP Primer by brush or roller at a minimum coverage of 1 litre per 8–10m².
• Non-porous or non-absorbent surfaces: Apply Gripset OP Primer at a minimum coverage of 1 litre per 12m².
• Green or damp surfaces with residual moisture: Apply Xpress Primer H2O Plus at a minimum coverage of 1 litre per 8m².
• Damp surfaces or rising damp: Apply 1 to 2 coats of Gripset E60 at a minimum coverage of 1 litre per 3m² per coat for mineral surfaces with residual moisture >80% RH (ASTM F2170) or >5% moisture content (ASTM F2659).

Detailing and bond breakers

Critical joints, junctions, penetrations, and cracks must be sealed prior to applying the membrane. Use one of the following systems:

• Option A (High Movement): Embed Elastoproof B50 Joint Band into a wet 150mm wide strip of P39 Membrane, press out all air pockets, and fully encapsulate with a second coat. Use prefabricated internal (90°) or external (270°) corners at junctions.
• Option B: Apply self-adhesive BRW PF Tape centrally over the joint, pressing firmly with a spatula or roller to remove creases.
• Option C: Install a bond breaker fillet at horizontal and vertical transitions using RLA Max SMP 25 sealant, tooled smooth.
• Penetrations: Fit Elastoproof Collars over protruding pipes and bed into wet membrane, seal with BRW PF Tape flanges, or apply a liberal bead of RLA Max SMP 25 sealant around the base.
• Static Cracks (1mm to 6mm) and Screw Holes: Clean out loose material, fill flush with RLA Max SMP 25, and overlay with RLA Waterproofing Bandage, Elastoproof B50, or BRW PF Tape.

Limitations

• Do not apply to areas when rain is imminent.
• Do not apply when the surface temperature is below 5°C or above 30°C.
• Do not use in areas subject to negative hydrostatic pressure.
• All finish coatings and toppings applied over this membrane must be solvent-free.
• When tiling directly over the cured membrane, you must use polymer-modified cement-based adhesives such as Gripset C-LITE, C-MASTIC, or C-RUBBER.
• If applying a screed, render, or concrete topping over the membrane, Gripset 11Y must be incorporated into the mix as a bonding agent.