Which Primer Do I Use Before Plastering?

Choosing the right primer before plastering depends on the surface you're working with and whether you need to control suction, improve water resistance or create additional grip.

There are three main options: PVA, SBR and Pre-Grit.

Why prime before plastering?

Priming prepares the background so the plaster can bond and dry correctly. Depending on the surface, it can:

• Improve grip between the background and new plaster.
• Control suction so porous surfaces don't draw moisture out of the plaster too quickly.
• Seal dust and loose particles that could affect adhesion.
• Promote even drying, reducing the risk of cracking and poor adhesion.

PVA – for porous internal surfaces

PVA is the traditional, cost-effective option for standard internal plastering applications.

On absorbent surfaces such as old plaster or brick, Bond It PVA Bond controls suction and prevents the background from drawing moisture too quickly from freshly applied plaster.

Apply two diluted coats before plastering. The first seals the porous background, while the second provides the bonding layer. Plaster should be applied while the second coat remains tacky.

Best for: General internal dry rooms, old plaster, porous brick and other absorbent backgrounds.

Avoid: Using neat PVA, allowing the second coat to dry completely, or leaving heavy puddles and runs.

SBR – for demanding or moisture-prone areas

SBR (Styrene Butadiene Rubber) is an alternative to PVA where greater water resistance, durability and adhesion are required.

Bond It SBR Admixture is a versatile bonding agent and admixture that can be used as a primer before plastering, particularly in demanding or moisture-prone applications.

Unlike PVA, SBR doesn't re-emulsify when exposed to moisture once cured, making it particularly suitable for more demanding applications.

Best for: Bathrooms, kitchens, external walls, damp-prone areas, sand-and-cement renders and highly porous backgrounds such as old brick or breeze blocks.

Depending on the substrate and application, SBR can be used neat or diluted, so always follow the product instructions.

Avoid: Applying SBR over dusty, greasy or contaminated backgrounds. Surfaces should always be clean and properly prepared first.

Pre-Grit – for smooth and low-suction surfaces

If you're plastering a smooth, painted or low-suction surface, controlling suction isn't the main issue – you need to give the plaster something to grip.

Bond It Pre-Grit contains fine silica aggregate that dries to form a hard, textured surface. Think of it as creating a Velcro-like mechanical key between the background and the new plaster.

It's supplied ready mixed, so there's no dilution or need to plaster while the product remains tacky.

Apply one even coat with a suitable brush or medium/long-pile roller and allow a minimum of 24 hours to dry before plastering.

Best for: Smooth concrete, glossy or low-suction surfaces, suitable tiled surfaces and existing plaster being prepared for re-skimming.

Avoid: Diluting the product, applying it too thickly or plastering before it has completely dried.

So, which plaster primer do I need?

A simple way to choose is:

Porous internal surface? → PVA
Need greater water resistance and adhesion? → SBR
Smooth or low-suction surface? → Pre-Grit

Correct surface preparation is essential whichever method you use, so always check the relevant product instructions before application.