Pool Cracks: Surface Crazing or a Structural Crack?

A crack in a pool is either in the finish (the plaster, quartz or pebble surface) or in the concrete shell underneath. A Florida plaster maker says you cannot be sure which kind you have without draining the pool.

How to tell if a pool crack is structural

SGM, a Florida maker of pool plaster, is direct about it: “It is virtually impossible, without draining the pool’s water and cutting out a sample of the plaster, to determine whether or not this is a structural crack in the concrete shell or just a normal shrinkage crack.” So no checklist on a website can settle it. What you can do from the deck:

• Look at the pattern. A web of fine lines across the surface is what SGM describes as check or shrinkage cracking, “commonly” minor surface cracks.
• Check whether it leaks. Run the bucket test on is your pool losing water. A crack with no water loss is less pressing than one with it.
• Tap around it. SGM lists “areas that sound hollow when tapped” among the signs that a finish needs repair or resurfacing.

A contractor who sees the pool in person is the honest answer to the rest.

Surface crazing and check cracks

Check cracks, also called shrinkage cracks, form as the finish cures. SGM says they are “inherent to some degree in all cement mortar mixes, and are not considered a material defect”, and that “accelerated drying causes these types of cracks, which can be attributed to weather conditions such as wind, temperature and humidity.” Its installation manual adds that “hot, dry shells will cause rapid setting of the plaster and result in check or shrinkage cracking and delamination.”

Structural cracks in the shell

“Plaster is not designed to provide structural strength,” SGM says, and “structural cracks in the concrete shell may create cracks in the plaster that are beyond the control of the plasterer.” A crack in the shell is a different repair from a crack in the finish, and finding out which it is may mean draining the pool. Draining in Lee County has its own rules: the Florida Building Code requires a hydrostatic relief device where a water table is anticipated. Draining a pool in Florida explains why, and pool resurfacing covers what a drain and refill involves.

What each repair involves

SGM’s bulletin describes three levels of repair for minor check cracks. Filling the pool and keeping the plaster fully submerged can make the minor voids “expand and become difficult to detect”. In some slight cases, polishing the finish reduces how visible they are. In a more severe case, the crack is cut out with a concrete saw and filled with matching finish, though “it is nearly impossible to match the color when patching plaster.”

When cracks are part of wear across the whole pool, SGM says “resurfacing is the better fix”. A crack that leaks needs pool leak detection first, so the repair goes where the water is going. A shell crack found during a larger project can be handled as part of pool remodeling.