For subfloors and walls showing signs of rising damp, or green concrete slabs that need immediate coating, RLA Moisture Seal Primer acts as a two-part water-based epoxy barrier to block moisture vapour transmission and prevent subsequent floor finishes from blistering, bubbling, or delaminating. It seals mineral substrates prior to applying levelling compounds, membranes, adhesives, or decorative finishes, and resists hydrostatic pressure in below-ground installations like lift pits and basements.
How it works
This solvent-free, low-VOC epoxy system penetrates concrete, screeds, and masonry to form a dense, non-porous barrier. When mixed in a 1:1 ratio by volume, the cured film withstands substantial water pressure on negative-side underground structures and blocks water vapour transmission. It is fully compatible with RLA membranes, adhesives, and levelling compounds, and complies with AS 4020 for potable water storage applications.
Numbers that matter
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2.5 bar hydrostatic resistance: Withstands up to 25 metres of negative or positive hydrostatic head pressure, preventing water seepage in below-ground basements, lift pits, and retaining walls.
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1.8g/m²/24 hours water vapour transmission: Tested to ASTM E96 (Desiccant method) at a 2-coat thickness of 200 microns DFT to stop rising damp from bubbling overlaid vinyl, timber, carpet, and epoxy coatings.
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4-hour recoat window: Allows fast multi-coat buildup at 23°C and 50% relative humidity, with full drying for finishes in 24 hours.
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2-hour pot life: Generous working time to mix, apply, and work the epoxy into porous substrates before curing begins in the pail.
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10-day water immersion cure: The required curing period before putting the treated surface into service for potable water storage.
Where to use it
This primer is suitable for application over the following substrates:
- Concrete and concrete blocks
- Glass reinforced concrete (GRC)
- Sand and cement screeds and renders
- Masonry surfaces
- Timber
- Compressed fibre cement sheeting, including James Hardie Scyon™ Secura™
Application standards
Coverage and film thickness must be adjusted to match the job requirement:
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As a general primer: Apply 1 coat at 1 L per 10m² to achieve 100 microns WFT (50 microns DFT) over approved substrates like James Hardie Scyon™ Secura™ before applying RLA waterproof membranes.
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As a vapour barrier: Apply 1 coat at 1 L per 5m² to achieve 200 microns WFT (100 microns DFT) over green concrete or screeds before installing liquid membranes.
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As a moisture barrier / hydrostatic coating: Apply 2 coats, each at 1 L per 5m² (total dry film thickness of 200 microns) for subfloors, rising damp, efflorescence control, and potable water immersion. Apply the second coat at right angles to the first.
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High-strength repair mortar: To patch surface defects or build waterproof fillets, mix 1 part mixed Moisture Seal, 1 part Portland cement, and 3 parts fine washed sand by volume, then apply with a spatula or trowel.
Preparing for subsequent finishes
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Paints, epoxies, and liquid membranes: Overcoat within 72 hours under normal conditions. After 72 hours, the cured surface must be lightly sanded with 240-grit sandpaper to promote mechanical adhesion before applying the top coating or an additional coat of Moisture Seal.
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Tiling, screeding, and cementitious levelling: When applying polymer-modified tile adhesives, engineered screeds, or floor smoothing compounds, broadcast fine dry sand into the wet second coat of Moisture Seal at a rate of 750g/m² (minimum 90% coverage). Sweep or vacuum up excess sand once dry. Alternatively, for green substrates only, prime the cured first coat of Moisture Seal with RLA Universal Primer before pouring levelling compounds.
Limitations
- Do not apply if surface or ambient temperatures are below 10ºC or above 35ºC.
- Cure rates slow dramatically when temperatures fall below 10ºC or relative humidity exceeds 80%. Do not apply if rain is imminent.
- Do not apply over standing water or onto steel and metal surfaces.
- For structures subject to active water leaks under hydrostatic pressure, treat and stop the active leaks with a hydraulic water plug cement before applying Moisture Seal.
- Must be covered with floor toppings, coatings, or conventional floor coverings; this product is not designed as a trafficable surface or a finished coating under permanent UV exposure.
- Provide mechanical ventilation when curing inside enclosed tanks, pits, or reservoirs to allow water evaporation.
