How To Fill a Gap Between a Brick Wall and Swimming Pool

How do you fill the gap between a brick wall and a swimming pool?

If the gap you are looking at is the one under the edge coping pavers or tiles, use Selleys Brick & Concrete Silicone Sealant. It is a waterproof seal with superior adhesion and resistance to lifting, and it gives a long-lasting flexible joint between the masonry and the pool surround.

The reason a silicone is the right answer here rather than a water-based gap filler comes down to two things: this joint gets wet constantly, and it moves a lot. A pool surround sits between a concrete shell and a brick or paved edge, and those two elements expand and contract at different rates in the sun. Brick & Concrete Silicone is rated at ±50% movement capability (ISO 9047, Method B), which is double what the water-based No More Gaps products carry. That headroom is the whole reason the joint survives a few summers.

What the numbers mean in practice

Skin time	70 minutes (23°C, 50% RH)
Tooling time	35 minutes
Tack-free time	90 minutes
Cure rate	2mm per 24 hours
Full cure	Approximately 72 hours
Movement capability	±50% (ISO 9047, Method B)
Tensile strength	1.2 MPa

These are indicative figures, not intended for the preparation of specifications.

The 35 minute tooling time is generous by silicone standards — most wet area silicones give you five to ten minutes — so you can lay a long run around a pool edge and still come back and tool it properly. The trade-off is at the other end: a 2mm per 24 hour cure rate means a bead 6mm deep is still curing three days later. Plan the job so the joint is not flooded, walked on or scrubbed during that period, and expect full cure at around 72 hours.

Where this sealant suits and where it does not

Brick & Concrete Silicone is intended for joints in walls, patios and floors, fencing, window joints and expansion joints in concrete around the home. It bonds to bricks and mortar, fibre cement, metal, ceramics, porcelain, concrete, marble and stone, wood and most plastics.

The limitations matter a great deal around a pool, so read these before you buy:

• Not suitable for below waterline applications. This is the important one. The product is for the joint under the coping, above the water — not for sealing anything that sits permanently submerged. A leak below the waterline is a different job and a different product.
• Not for use in below ground applications.
• Not paintable. Complete any painting seven days before you apply the sealant.
• Not for use on polyethylene, polypropylene or Teflon. Pre-testing on plastics is recommended.

If your pool is fibreglass and the joint you are sealing is between the coping tile and the top of the shell, the answer is different again — see the best product to seal a fibreglass swimming pool.

How to apply it

1. Rake out any old, failed sealant and loose mortar. Silicone bonds to the substrate, not to the remains of the previous bead.
2. Clean the joint so both faces are free of dirt, dust, grease and loose material, and let it dry. On a pool edge that means giving it time after rain or a hose-down.
3. Cut the nozzle to the width of the joint and cut it at an angle. Fit it to the cartridge and load a caulking gun.
4. Extrude the sealant into the joint with steady pressure, forcing it into the gap so it makes full contact with both faces rather than bridging across the top.
5. Tool the bead with a spatula within the 35 minute tooling window, so it is compacted into the joint and finished with a smooth face that sheds water.
6. Leave it alone. Skin forms at about 70 minutes, tack-free at 90 minutes, and full cure takes around 72 hours at 2mm per day.

Common questions about sealing a pool surround

Can I use No More Gaps for this joint instead?

No. The No More Gaps water-based fillers direct you to a Selleys silicone sealant where excessive joint movement occurs or where the area is prone to frequent water immersion. A pool coping joint is both.

Can I paint over the sealant to match the coping?

No. Brick & Concrete Silicone is not paintable — any painting has to be finished seven days before the sealant goes on.

Will it seal a leak below the water line?

No. The data sheet is explicit that it is not suitable for below waterline applications. It is for the joint above the water, under the coping pavers or tiles.

How long before the pool can be used again?

Allow for full cure at around 72 hours, and remember the cure runs at about 2mm per 24 hours, so a deep bead takes proportionally longer than a shallow one.

How much movement will it take?

±50% movement capability under ISO 9047 (Method B), which is why it suits the joint between two elements that heat and cool at different rates.

Will it stick to pavers and natural stone?

Its listed substrates include bricks and mortar, concrete, ceramics, porcelain, marble and stone, so yes, provided the surface is clean, dry and sound.

What about a plastic pool edge or a plastic drainage strip?

Do not use it on polyethylene, polypropylene or Teflon, and pre-test any other plastic in an inconspicuous spot first.

How long do I have to tool the bead?

About 35 minutes, which is unusually forgiving. After the 70 minute skin time, tooling will tear the surface rather than smooth it.

Can I use it below ground, for example on a retaining wall behind the pool?

No — below ground applications are excluded in the limitations.

Is there a related guide for pool edges?

Yes — how to repair loose pool tiles covers the neighbouring problem of tiles lifting around the waterline.