Start by identifying the crack and your pool type
The right repair depends on two things: what your pool shell is made of and what kind of crack you have. Concrete, gunite and shotcrete pools crack differently from fiberglass shells, and vinyl liner pools do not crack in the same way at all (a liner tears or develops holes instead).
Many cracks are cosmetic. Thin lines in the plaster surface are common in older pools and may not leak. Others go all the way through the shell, lose water, or signal that the ground or structure is moving. Treating the second kind like the first usually means doing the job twice.
Is the crack structural?
No single test settles this, and a pool professional or structural engineer is the right person to decide. These signs make it more likely that a crack is more than cosmetic:
- The crack is wide, or wider at one end.
- One side of the crack sits higher than the other (the pieces have shifted).
- The crack runs through the pool deck or coping as well as the shell.
- The crack keeps growing or reopens after being patched.
- The pool is losing water steadily, or the wall or floor appears to be bulging or sagging.
- Tiles are popping off or the deck is separating from the pool.
If you see several of these, stop and have the pool inspected before you drain it or apply any patch. Hairline cracks that do not leak and do not change over time are often only monitored or patched cosmetically, but it is reasonable to have a professional take a look if you are unsure.
Confirm the crack is leaking
A crack is not necessarily the reason the pool is losing water. Before spending money, check:
- Rule out evaporation and plumbing. A common home test is to compare the water level in the pool with a bucket of pool water set on a step, both marked at the same level. If the pool drops noticeably more than the bucket, the pool is likely leaking.
- Look at where the water stops dropping. If the level settles at a certain height, the leak is often at or near that height.
- Try a dye test. With the pump off and the water still, squeeze a small amount of leak-detection dye or dark food coloring near the crack. If the dye is drawn into the crack, that crack is likely leaking.
Cracks are not the only source of leaks. Skimmers, light niches, returns and plumbing lines are also common culprits, so a leak detection service may be worthwhile if the dye test is inconclusive. For winter-specific situations, see our guide to an inground pool leaking in winter.
Before you drain: water level and ground pressure
Pool shells are designed to carry water weight and to resist groundwater pushing from outside. Draining a large amount of water, especially when the ground is wet or the water table is high, can in some cases allow groundwater to lift or damage the shell. For a repair above the waterline you usually only need to lower the water a few inches below the damage.
Do not fully drain an inground pool without checking with a pool professional or the manufacturer or builder first. Also check local rules about where pool water can be discharged.
Repairing a crack in a concrete or gunite pool
Surface hairline cracks
Cracks that are only in the plaster layer are often addressed with a cement-based pool patch or a plaster repair product. The process is much like the one in our guide to DIY pool plaster repair: lower the water below the crack, remove loose material, clean the area, apply the patch, and let it cure per the product directions.
Leaking cracks
For a crack that passes through the shell, common repair approaches include:
- Epoxy: used to bond and fill cracks in concrete (the injection steps are similar to those in repairing a crack in a concrete wall). Many products are made for pools; check that the one you choose is rated for wet or submerged use if that applies.
- Polyurethane foam injection: low-pressure injection kits are sold to seal leaking cracks and joints in concrete pools. The foam expands to fill the crack. Follow the manufacturer’s instructions closely.
- Hydraulic cement: sometimes used for patching actively leaking spots, though it is typically a short-term or supporting measure rather than a fix for movement.
The usual sequence is to find and mark the crack, open it slightly with a chisel or grinder so the repair material can bond, clean out dust and debris, apply or inject the repair material, then finish and cure before refilling. Wear eye protection, a dust mask or respirator, and gloves, since grinding concrete creates fine dust and many repair products can irritate skin and eyes.
Structural cracks
Structural cracks are often stabilized with metal or carbon fiber staples (also called stitches) set into slots cut across the crack and bonded with epoxy, followed by sealing and resurfacing. This is skilled work and the right design depends on why the crack formed. If the cause, such as soil movement, is not addressed, the crack may return. This is a job where a pool contractor or engineer is worth the cost.
Repairing a crack in a fiberglass pool
Fiberglass pools usually show cracks in the gel coat first. Surface crazing and small cracks can often be repaired with a fiberglass repair kit. The typical steps are to grind or sand the damaged area, apply fiberglass cloth or structural putty with resin, let it cure, sand it smooth, and apply a color-matched gel coat. Matching color and finish can be hard, so many owners hire a fiberglass pool repair specialist.
Large cracks, cracks accompanied by bulging, or shells that appear to be flexing may indicate movement behind the shell and need professional assessment.
What about vinyl liner pools?
Vinyl liners tear or puncture rather than crack. Small holes can often be patched with a vinyl patch kit, including some that work underwater. Cracks in the pool’s concrete or steel wall behind the liner are a different matter and need to be inspected by a professional.
What is the best crack filler or sealant?
There is no single best product, and the answer depends on the shell material, whether the crack is moving, and whether the repair will be above or below the waterline. As a general guide:
- Epoxy for bonding and filling non-moving cracks in concrete.
- Polyurethane for sealing leaking cracks that may flex slightly.
- Cement-based patching mix for surface chips and plaster-layer cracks.
- Fiberglass resin and gel coat for fiberglass shells.
Always read the product’s label for the surfaces it is designed for and whether it is safe for pool use, then follow the cure times before refilling.
Can you repair a pool crack underwater?
Some products are formulated for underwater application, such as certain putties, epoxies and vinyl patches, and they are commonly used for small repairs. They are usually seen as convenient or temporary fixes. For lasting repairs to concrete cracks, most guides recommend lowering the water level below the work area so the surface can be cleaned and the material can cure properly. If a crack is leaking significantly, an underwater patch is unlikely to be enough.
Common mistakes
- Patching over a crack without finding out why it formed.
- Skipping surface preparation, which causes the patch to fail.
- Draining the pool more than necessary.
- Using a general-purpose caulk or filler not intended for pool water or chemicals.
- Refilling before the patch has fully cured.
When to call a professional
Call a licensed pool contractor, leak detection specialist or structural engineer if:
- The crack appears structural (see the signs above).
- You cannot locate the leak, or water loss continues after a repair.
- The pool has shifted, bulged or separated from the deck.
- You need to drain the pool substantially.
- The repair involves cutting into the shell or structural reinforcement.
Insurance sometimes covers certain kinds of sudden damage but often excludes wear and tear or gradual leaks. Check your own policy or ask your insurer.
FAQ
Can I fix a crack in my pool myself? Small, non-structural cracks and chips often can be repaired by a careful DIYer. Structural cracks should be assessed by a professional.
How do I know if a pool crack is structural? Look for widening, offset edges, continued growth, or cracks that extend into the deck. If in doubt, have a professional inspect it.
Do I need to drain the pool to repair a crack? Often you only need to lower the water below the crack. Avoid fully draining the pool without professional advice.