The problem

The damage starts at the skirting

Concrete holds moisture, and an uncoated basement belt passes it into the masonry built on it. The wall finish shows it first: paint lifting and flaking, plaster softening and letting go, mould spreading across the surface.

Damp lifting the paint off an interior wall in a ragged band just above the skirting tiles, bare plaster showing through — Paint lifting in a band just above the skirting, down to bare plaster.

Grey-black mould spreading across the lower part of a painted wall, paint and plaster blown off the render at one side — Mould across the paint, and plaster blown clean off the render.

Product description

A separation layer between concrete and wall

PRIME GUARD AQUA BLOCK is a high-performance moisture-blocking coating developed specifically for concrete basement belts, concrete door frames and concrete window frames. It forms a durable protective barrier that helps prevent moisture migration from concrete surfaces into adjacent walls, reducing dampness and moisture-related damage.

The coating is designed to create a separation layer between concrete and masonry, helping protect paint, plaster and wall finishes from moisture penetration.

How Aqua Block works

It penetrates and bonds to the concrete surface, forming a continuous waterproof barrier rather than a film that sits on top.
On basement belts, door frames and window frames, that barrier blocks moisture movement through the concrete and reduces water penetration from the surrounding areas.
Keeping water out helps maintain structural integrity and reduces the risk of dampness-related damage to the finishes around it.

“Direct apply”: suitable for

Concrete basement belts
Concrete door frames
Concrete window frames
Concrete beams
Concrete columns
Masonry contact areas
Damp-prone concrete surfaces

Water beading into spheres on a coated dark surface instead of soaking in — Water beads on the cured film instead of wetting the concrete.

Key benefits

What you get from it

Blocks moisture transfer
Helps prevent wall dampness
Waterproof barrier protection
Long lasting durability
Strong adhesion to concrete
Reduces moisture-related damage
Easy application
New construction & renovation

Application

Two coats, one working day

It goes on during construction, before the wall does: on the top of the basement belt the wall will be built on, and on the face of a concrete frame that meets the wall.

Diagram of a stone basement with its concrete belt on top, Aqua Block coating the top face of the belt — Basement belt: coat the top of the belt, then build the wall on it.

Diagram of a concrete frame with Aqua Block on the face that meets the wall, moisture arrows stopping against the coat — Concrete door or window frame: coat the face that meets the wall.

1

Prepare the concrete

Make sure the surface is clean, dry and free from dust, grease, oil, rust and loose particles. Repair cracks or damaged concrete before you start.
2

Stir, then apply the first coat

Stir well before use. Brush or roller an even first coat of PRIME GUARD AQUA BLOCK directly onto the top of the belt, or the face of the frame that meets the wall.
3

Wait 2–3 hours, apply the second coat

Let the first coat dry for 2–3 hours to recoat, then apply the second coat over it.
4

Allow 5–8 hours for hard dry

Wait 5–8 hours for a hard dry, and allow complete curing before the wall is built on it or the surface is exposed to water. Keep the container tightly closed after use.