I have been seeing more and more swimming pool & spa rebound cracking in (gunite) pools and have been asked to post photos of what rebound cracks look like.
(This will article will be updated occasionally so check back for new information and photos.)
Rebound is excess gunite that bounces off the wall upon application that has a low cement to sand ratio and is weak in strength. It should be removed from the pool. Unfortunately, to save yardage, it is common practice for gunite crews to throw rebound into the spa to form and shape the steps. Upon immediate visual inspection it is impossible to see any issues. As the pool/spa ages and settles, the steps built with low cement content don’t have the strength to withstand the stress and the weakest areas crack. Usually the crack runs horizontally under the step. By far, I see most rebound cracks in spas, typically on the top step or the foot well seat (I also see cracks in pool steps and pool love seats, just not as frequent as in the spa).
Make no mistake: workmanship guidelines (published in ACI) state that REBOUND SHOULD BE REMOVED from the pool!
Photos of rebound cracks:
(note: a pool engineer taught me to listen for the hollow areas above rebound cracks by tapping on the plaster with a crow bar).
In my experience, rebound cracks typically don’t allow water to escape the pool/spa shell.
Although the cracks are extremely unsightly, I have found that most pool owners wait until resurfacing to correct the issue. At resurfacing, the plaster company will strike the cracks with a jack hammer and the loose material will effortlessly fall off. The step(s) are rebuilt with plaster and is no longer an issue.
Excellent reference articles on rebound:
– Use of Rebound in Swimming Pool Construction
Mike the Poolman
Pool Service & Repair in Folsom, CA since 1995