Collection: Primers & Surface Preparation

Not always — it depends on the substrate type and membrane system. Water-based acrylic membranes often require an acrylic primer for bonding and surface stabilisation, while two-part polyurethane membranes usually need an epoxy or compatible solvent-based primer to control moisture and improve adhesion. Some products (like Mapelastic Smart) are self-priming on damp, clean concrete. Always check the system data sheet — priming is about creating the right bond, not just following a rule.

Acrylic primers are mainly for absorption control and surface bonding, whereas water-based epoxy primers (such as Planiseal MR or Gripset E60) also act as moisture and vapour barriers. Acrylics prepare the surface — epoxies seal it. Use acrylic primers for general wet areas or porous substrates, and epoxy primers when dampness, negative pressure, or hydrostatic risk is present.

Yes, but only if the primer is designed for it. Many water-based epoxies and moisture-tolerant primers are formulated for saturated surface-dry (SSD) conditions. However, most acrylic primers need the substrate to be visibly dry. Applying the wrong primer to a damp slab traps moisture, leading to blistering or bond failure.

A simple check: spray a small amount of clean water onto the concrete. If it absorbs evenly and darkens, the surface is open and ready. If water beads or sits on top, contaminants or laitance are present and need removal by grinding or mechanical abrasion. Good preparation ensures the primer penetrates rather than forming a skin on a dirty or sealed surface.

Use a water-based epoxy primer such as Mapei Planiseal MR or Gripset E60. These primers tolerate residual moisture and create a vapour barrier that prevents debonding of subsequent waterproofing layers. They are ideal for early-age concrete or internal wet areas where residual moisture can’t fully evaporate before coating.

Yes. Water-based epoxy primers like Planiseal MR can be applied as a negative-side moisture barrier on internal slabs or basement walls where dampness is migrating through. Once cured, flexible membranes such as Mapei Aquadefense can be applied directly over the primed surface. This approach is common in below-ground bathrooms or retaining walls where moisture pressure is present.

Remove dust, laitance, oil, and efflorescence by mechanical grinding or wire brushing. The goal is an open, clean surface with consistent porosity. Patch voids with compatible repair mortars (Planitop Fast 330, R4, or similar). Vacuum all dust before applying primer. A properly prepared substrate ensures even absorption and strong adhesion — skipping this step is the main cause of primer failure.