Ardex Multiprime Primer

For porous substrates including CFC sheet, concrete, masonry, and jointing compound over plasterboard, ARDEX Multiprime prepares the surface to improve the adhesion of subsequent approved ARDEX products. This water-based liquid primer dries quickly in both internal and external applications, providing a reliable bond interface across varying substrate porosities.

How it works

Multiprime penetrates porous substrates to bind residual fine dust and equalise suction. By regulating the absorption rate of the surface, it prevents subsequent screeds, renders, or adhesives from losing water too rapidly into the substrate, preserving their strength and curing characteristics. The primer cures to a tough film with a minimum tensile strength of 5.03 MPa and a Shore Hardness A rating of 90, establishing a high-strength mechanical key on porous materials like autoclaved aerated concrete (AAC), screeds, and concrete blocks.

Where to use it

• CFC sheet: Seals the fibrous surface to ensure consistent adhesive contact.
• Jointing compound over plasterboard: Equalises the differing absorption rates between the paper face and the gypsum compound.
• Concrete and screeds: Prevents rapid water loss from overlying repair mortars, levelling compounds, or tile adhesives.
• Masonry, concrete blocks, and AAC: Shuts down high-suction substrates (AAC requires a second coat of Multiprime to completely seal the surface).

Numbers that matter

• 15 to 30 minutes drying time: Quick window at 23ºC and 50% relative humidity to keep the installation moving; drying times will extend on highly porous substrates or in cooler temperatures.
• 8m² to 9m² coverage: Total coverage yield per 15L pail based on a two-coat application, varying with substrate porosity and application technique.
• 5.03 MPa tensile strength: High cohesive bond performance to ensure the cured primer layer resists shear forces under stress.
• 10ºC to 35ºC application range: The critical temperature window for both the ambient air and the substrate to ensure proper film formation.

Limitations

• Do not apply if ambient or substrate temperatures are below 10°C or above 35°C.
• Do not add water or solvents to the product.
• Do not apply if rain is imminent.
• Do not use on concrete or masonry with moisture levels exceeding 80% relative humidity (tested to ASTM F2170) or 15g/m²/24hrs moisture vapour emission rate (tested to ASTM F1869). For these wet conditions, a minimum of two coats of ARDEX WPM 300 (HydrEpoxy) must be used.

Installation

Remove all dirt, dust, curing compounds, oils, grease, surface sealers, existing coatings, and other contaminants before applying. Prepare the surface to ensure it is clean, dry, sound, and free from sharp edges. Damaged concrete between 2mm and 30mm deep should be repaired with ARDEX A 46 before priming. Spalling concrete must be treated using the ARDEX Concrete Repair range, such as ARDEX BR 345.

Shake the container thoroughly before use. Apply evenly with a brush, roller, or sponge to the prepared substrate. Ensure the primer is completely dry before applying any subsequent ARDEX products. Clean all application tools and equipment with water and detergent before the primer dries; cured material requires mechanical removal.