Swimming Pool Blog
by Rob Cox, January 12, 2010
Frost Heave on a Concrete Pool Deck
Our last blog post on what to do with Frozen Pool Equipment encited a lot of responses from worried homeowners. I got several comments about busted heat exchangers and locked up pool pumps. One reader sent in questions about his deck suddenly raising up. Where it once was level with the pool coping, as it should be, it was now about 1/2" higher in one area. See photo of John's trouble below. He was especially upset at the time, being that he had just spent $10,000 for a new pool deck about 3 years ago.
I told John that chances are the deck will settle back into place after the weather turns - but "perhaps not". Hard to see in the picture, but the caulking has ripped and this section will need to be recaulked once the weather permits. In fact, my first question to John was "Did you have the caulking in place between the deck and the coping?" This is one reason to have a good caulking joint, to keep out the water that can erode the soil under the deck, and which can freeze, expand with such force, that it will lift up a concrete slab.
The photo at the top of the page is obviously a summertime photo. The problem here is not Frost Heave, but a problem with expansive clay soils used beneath the deck, which when wetted excessively, have incredible lifting power. John may also have a bit of marine clay or other expansive type soil beneath his deck, which more than soaks up water, they are actually electrically attracted to each other.
A third type of situation occurs when loose fill is used beneath the pool deck, especially where the ground slopes off near the edge of the concrete. A little "soil slip" and a little erosion, and you'll find the rear of the slab drops down, and the front of the slab raises up. This is not really heave at all, but a settling and slipping of the fill dirt used beneath the pool deck.
So what to do if your deck has done the 'ol heave ho? Not much you can do really. Just hope and pray that it settles down flush again. Usually it does. The caulking will need to be redone, but not much else can be done. Do consider the flow of water around the pool, does rain runoff come near this area? Redirecting runoff water can be helpful in preventing frost heave, to keep the soil beneath the deck drier.
If your pool deck is lower than the coping stone, a "sinking slab", you now have a potential trip hazard around the pool. To solve extreme slab sink, you can hire a team to come out and "slab jack", or pump a concrete mixture beneath the deck, although for small jobs removal and replacement will be cheaper. If your slab has settled only 1/2" or so, you can caulk the joint with an upward angle to reduce the potential for a trip and fall (and potential drowning) hazard.
John, thanks for a good blog topic. Pool ownership - it's always something!