Pool Deck Crack Repair: How to Fix Cracks and the Coping Joint

What do you need to repair a pool deck crack?

A flexible, UV-stable crack kit, dry silica sand and a few hand tools. A pool deck sits in full sun, gets wet every day and moves with the seasons, so a rigid filler cracks loose and a filler without UV protection breaks down.

How do you repair cracks in a pool deck?

Open up thin cracks, clean and dry them, pack them with sand soaked in urethane, then top them with a polyurea filler. That’s the method in the UV slab kit’s instructions, and it suits cracks up to 1/4 inch with flush edges.

1. Check the crack

   Lay a straightedge across it. If one side is higher, or it’s wider than 1/4 inch, read the section on cracks that need more than a filler first.

2. Protect the water

   Lay plastic along the coping near the crack so dust doesn’t end up in the pool.

3. Open up thin cracks

   For cracks 1/8 inch wide or less, the kit’s instructions say to grind the crack out to 1/4 inch wide and 1/4 inch deep. Wider cracks skip this step.

4. Clean and dry the crack

   Vacuum out the dust and loose concrete. The instructions say the crack must be dry, so keep splash and sprinklers off the deck until it is.

5. Prime with urethane

   Wet the inside of the crack with the kit’s urethane.

6. Pack in sand

   Pour dry silica sand into the crack until it’s 1/4 inch below the surface.

7. Soak the sand

   Saturate the sand with more urethane and let it set for about 30 minutes.

8. Top it off and scrape

   Fill the last 1/4 inch with the polyurea filler, which levels itself. Scrape any overflow flush with a razor scraper.

How do you fix cracks around pool coping?

Most cracks around pool coping aren’t cracks. They’re the joint between the deck and the pool, where the old sealant has split or pulled away. You fix it by cutting out the old sealant and resealing the joint with a flexible filler.

That joint is there on purpose. The pool shell and the deck are separate pieces of concrete that move differently, so they’re kept apart. The NRMCA describes this kind of isolation joint as one that lets the slabs have independent vertical and horizontal movement (opens in a new tab) without cracking.

Pool rules require the seal. Michigan’s swimming pool rules say the joint between the coping and the walkway must be sealed with a flexible waterproof sealant (opens in a new tab), and Maryland’s require a durable, watertight sealant (opens in a new tab) at the coping to deck joint. Those rules are written for public pools, but the reason applies to yours: water that gets into the joint soaks the soil under the deck.

Here’s the pool deck joint repair, start to finish:

1. Cut out the old sealant

   Slice along both sides with a utility knife and pull it out. Scrape the joint walls clean down to bare concrete and coping.

2. Clean and dry the joint

   Vacuum out the debris and let the joint dry fully.

3. Set backer rod

   Press in backer rod slightly wider than the gap so it fits snug. It sets the depth of the sealant and keeps it from sticking to the bottom of the joint.

4. Tape the edges

   Run painter’s tape along the coping and the deck edge for a clean line.

5. Fill the joint

   Fill it flush with the deck. Self-leveling fillers flow flat on their own; tool non-sag ones smooth.

6. Pull the tape and let it cure

   Remove the tape while the filler is wet, then keep traffic and water off it for the cure time on the label.

The backer rod guide covers sizing. For the filler, use one made for control and expansion joints, not a crack filler or caulk. The expansion joint repair guide has more on joint fillers.

If the coping stones themselves are loose, cracked through, or the tile line below them is cracking, the problem is in the pool’s top beam, not the deck. That’s a job for a pool contractor.

How long before you can use the pool deck again?

About an hour in mild weather. The polyurea used to top cracks and fill joints takes light foot traffic in 30 minutes and full traffic in 60 minutes at 70°F, according to its data sheet. Apply it only when the concrete is at least 50°F.

Cold slows every cure. Keep splash-out off the repair until it's ready for full traffic.

What mistakes make a pool deck repair fail?

Water and rigid fills cause most of them. A crack that was damp when filled, or a joint packed with mortar, comes loose within a season or two.

• Filling a wet crack. Pool decks rarely dry out on their own. Keep splash, sprinklers and wet feet off the area until the crack is dry.
• Putting mortar or caulk in the coping joint. The joint has to move. Use a flexible joint filler made for it.
• Skipping the grinding on a thin crack. Filler can’t get into a crack 1/8 inch or narrower, so it sits on top and peels off. Open it up to 1/4 by 1/4 inch first.
• Leaving a ridge. Filler above the surface catches bare toes. Scrape the overflow flush before it sets.
• Filling a deck that has moved. If the deck sank or drains toward the pool, the crack will open again. Fix the movement first.

Is it a crack or a joint in the pool deck?

Straight lines are joints. Control joints are the grooves cut or tooled into the deck to give it a planned place to crack, and a crack running down the bottom of one is doing its job. Random, wandering lines across a panel are cracks.

The crack or joint guide shows how to tell them apart. Control joints on a pool deck get the same flexible joint filler as the coping joint if you want them sealed. Cracks get the urethane crack filler.

Which pool deck repair do you need?

Match the damage to the fix before you buy anything. A crack, an open joint and a deck that has moved each need something different.

When does a pool deck need more than a filler?

When it has moved. A deck section that has sunk, tilted back toward the pool, or has one edge higher than the next is sitting on soil that settled. Filling the crack hides that but doesn’t stop it.

Slope is the thing to check. Maryland’s pool rules set deck slope away from the pool at not less than 1/4 inch per foot (opens in a new tab), and no more than 1/2 inch per foot. If water now runs toward the coping or sits in puddles, the deck has moved, and every rain sends more water into the joint and the soil.

An offset edge is also a trip hazard on a wet, barefoot surface. Your options for a deck that has moved are lifting the slab, grinding the high edge, or replacing the section, and a concrete contractor can price those. If the pool shell itself is cracked, or a deck next to the house is moving along with cracks in the foundation, have a structural engineer look first.

Why do pool decks crack?

Mostly because of the soil under them and the water around them. Pool decks are often poured over soil that was dug out and backfilled around the pool, and they get wet constantly.

• Settling backfill. The soil around a new pool is backfill, and it can keep settling for years. The deck drops where it’s softest and cracks over the low spot.
• Water under the deck. An open coping joint or a deck that drains toward the pool lets water soak the soil, which softens it or, with clay, makes it swell.
• Joints too far apart. The NRMCA says joint spacing for a 4 inch thick slab should be about 10 feet (opens in a new tab). Decks with long, narrow panels crack between joints.
• Freeze-thaw. In cold climates, water in saturated concrete expands as it forms ice (opens in a new tab), which flakes the surface and opens cracks wider each winter.

The why concrete cracks guide covers each cause in more detail.

How do you keep a repaired pool deck from cracking again?

Keep water out of the deck and the soil under it. Keep the coping joint sealed, point downspouts and splash-out drainage away from the deck, and seal the concrete once the repairs cure.

Check the coping joint every spring when you open the pool. A split in the sealant is a small fix if you catch it early. Left open, it lets water reach the soil under the deck.

For freeze-thaw protection, the NRMCA recommends sealing the surface with a commercial breathable sealer (opens in a new tab). On a pool deck, pick one that won’t make the surface slick when wet.

The sealing after crack repair guide covers which sealer to use over a repair and how long to wait.