What is a Pool Expansion Joint?


The pool expansion joint is an important (and usually overlooked) element of your in-ground swimming pool. Often the line of delineation between the pool itself and your deck, it’s pivotal in keeping the two structures separate and independent of one another. This keeps surrounding concrete as well as pool tile from cracking due to the materials’ tendency to expand and contract.

Do all pools have an expansion joint?

Almost all in ground pools that are thoughtfully constructed will have an expansion joint. This is usually the gap between the coping stones that surround the pool from the decking. The joint is usually filled with caulk or some kind of sealant that lets the materials on both sides of it move without causing serious damage to either.

If the concrete were poured right up to the coping stones without any room left for a pool expansion joint, you would have serious cracking when the deck expands during warm weather after having contracted in the cold of the winter.

When is the expansion joint caulked?

If your pool is new, you can see a foam strip that is installed inside the joint when the deck was poured that separates the deck from the coping stones. That is referred to as your perimeter expansion joint.

The expansion joint between the coping and the deck is typically caulked or filled with elastomeric sealant approximately 30 days after the concrete was originally poured. This gives the concrete time to settle and assume its permanent structure. If it is caulked before then, it may not align properly. REMEMBER to always clean out this area before caulking because that’s the only way to give you true alignment.

You will also need to keep an eye on the joint and conduct regular maintenance. More on that later!


What are the benefits of caulking the pool expansion joint?

Pools can cost a lot of money and in order to protect your investment, you need to seal all the gaps that water can penetrate. If water gets behind coping and/or the tile band and then freezes, the tile can become damaged. The pressure of the ice can push the tile out and crack it, costing you a pretty penny in repairs.

Ice seems harmless but can be one of the most destructive forces in nature. It can damage steel, concrete, rock, or anything else that it settles into. When you properly caulk the expansion joint around your pool, you keep out water that can freeze and expand, potentially damaging the coping and beam. Eventually, these two problems with damage your tile. If you have cracked tile, there’s a chance your beam has cracked all the way through.

The beam in your pool is the top 6 or 8 inches of the pool wall which holds the tile and coping. If the beam damage is unattended, it will get worse with time and will eventually crumble. The beam will then need to be reconstructed. To avoid this expense, caulking and maintaining the pool expansion joint should be high on your list of priorities.

Can I use sand instead of a sealant?

Sand is typically discouraged from use in filling expansion joints because it doesn’t have the ability to expand and contract the way you need a pool joint to. Sand is also prone to washing away and/or becoming contaminated with other elements. But the number one reason not to use it is because it isn’t as accommodating as foam and caulk.

When the expansion joint is full of sand, very little expansion can take place. So if you were ever in doubt about whether or not to caulk your pool, think no longer. It will save you money in the long run.

How do I caulk an expansion joint?

  • A good caulk job should always begin with surface prep. The sides of the joint need to be clean, dry, and solid. If you have newly poured concrete, NEVER begin caulking until the concrete has settled for 30 days.
  • You should have backer foam already in the joint (DON’T use sand) to give the caulk something to sit on top of.
  • Use an elastomeric sealant (self-leveling) that is meant for outdoor use.
  • Tape off the joint to keep things neat and shoot or towel the caulk into the joint to a depth of 3/8th-1/2” deep.
  • Remove the tape before the caulk sets up.
  • Check the caulking every year. If it starts to crack or pull away from either side of the concrete or decking, you’ll need to remove the existing caulking and conduct the job again. DO NOT just add new caulk over the top of the old. This is not very helpful, nor cost effective.
  • You can pay a professional to caulk the expansion joint. Most pool maintenance companies charge somewhere between $5-$10 per linear foot to complete the job.
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