Swimming Pool Blog

Pool Caulking with Vulkem SSL

Best Pool Community Q&A
by Mark Garcia June 17, 2016

pool caulkingWHAT IS POOL CAULKING? Fair enough question, not everyone knows what pool caulking is - the rubbery strip of sealant that's placed between the back of the pool coping and the edge of the deck. The purpose of pool caulking is to keep the joint from filling up with grit and debris, and also keeping water out of the joint.

HOW LONG DOES POOL CAULKING LAST? Swimming pool caulking doesn't last forever. If you get 5-7 years from it, you've had a good run. It breaks down from the sun, UV exposure. Pool caulking can also fail not by deterioration, but by separating from the sides, from movement of the pool and deck.

WHY IS POOL CAULKING IMPORTANT? Three reasons; first is that when rain and snow melt continually pours into the expansion joint and runs under the pool deck and up against the pool walls, it could cause some problems with erosion or corrosion. Soils that are saturated in winter can cause frost heave, which can lift and tilt the concrete slab when saturated soil freezes beneath. 

The second reason that caulking is important in the expansion joint around the pool is that it is an expansion joint, to allow room for the pool and deck to expand (when weather heats up), without bumping into each other. When the joint fills up with grit, sand and pebbles, the space between the two is filled and they can move as one, and guess who wins? Pool deck, every time.

The third reason for pool caulking maintenance is that you want to keep water out of the joint during winter. Water expands nearly 10% when it freezes, and when it fills the joint and small spaces under the coping stones, it can slowly cause damage to the pool by loosening coping stones and tile, or even cracking the beam of the pool.

OK, I'M SOLD - HOW DO I CAULK MY POOL? You could just call your local pool company, or handyman, who may charge in the neighborhood of $7 per foot, or about $1000 for the average pool, to remove and replace pool caulk. Alternatively, you can do it yourself, DIY style for under $200 in materials and a day's work. 


Don't just squirt new caulk over top of old caulk, because it will fail again soon. although for very small hole repairs or small gaps, you could. But for a complete caulking job, you start by removing the old caulking, using long razor knives. Box cutters have too short of a blade, a full size razor knife is what we use. You can also use a reciprocating saw to saw through the caulking on both sides or edges; a cordless model is safer around pools. The coolest tool is a handheld scraper tool. It's important to try to remove as much bits of caulking from the edges as possible, but it could be impossible to remove them all. As you remove the caulk, inspect the foam backer rod, or foam strip that is beneath the caulk. Chances are, it's toast, although in some cases, it may still be intact and functional. Some cleaning of the deck and coping edges may be prudent, to obtain the best bond or seal, all grease and dirt should be removed. A pressure washer can be used, or a scrub brush and small amount of cleanser. No need to go overboard, just make sure you have a clean surface before caulking.


This important barrier serves to prevent your expensive caulking from running straight down into the joint, and allows you to pour a consistent thickness of caulking. A solid 1/4-3/8in thickness is usually best, and the backer rod foam, which supports the 'bed' or ribbon of caulk, is necessary to be consistent and prevent caulk waste. As mentioned above, your current backer rod may be toast, or you may be able to reuse it, or some of it. Backer Rod should be purchased in sizes slightly larger than the width of the joint, as measured from side to side, so that it can be squeezed into place and position, properly.

Push the backer rod with a large putty knife or spatula, stretching it just slightly with your leading hand, and pushing down with a tool in your trailing hand. In spots where the width of the joint changes, you may have to stop, cut the foam, and switch sizes. In some places you may need to use the razor knife to slice the backer rod foam into two smaller widths, to take up room in a corner, for example, but for smaller width joints, it's best to use smaller width backer rod, to get the best seal against the sides. Speaking of the seal, spend the time to make sure that you have no leakers or weepers. Holes or gaps in your backer rod where the ($25 per tube) caulking will run through. You can test suspected areas with water, although self leveling pool caulk is much thicker, of course, but it seeks its own level and will run out of surprisingly small holes. Also look for areas where the pool deck and coping aren't even, be sure to push it low enough below the lowest side, which is usually the deck.

DON'T USE SAND. Sand in the joint is the worst thing you can do, it does not compress and essentially removes all the expansion from the joint. In fact, if you notice areas of your expansion joint where it's filled with debris, sediment, concrete, plaster, etc... it may be good to remove with a pressure washer or wet/dry vac. It's important that your expansion joint be 'true', and clear to the earth, so that your pool and pool deck have room to expand independently, without bumping into each other.


For supplies, you'll need a large caulking gun, for the quart tubes. You'll also want to wear some type of thin gloves, and put on your old clothes. Cut a few large squares of cardboard that you can move around the pool with, and place a few rags in your back pockets. Clean the pool deck off and check your phone for dry weather ahead. The joint should also be very dry before caulking; wet joints trap wet air which rises through the caulk as bubbles. Self Leveling pool caulk, and even Vulkem SSL Semi-Self Leveling pool caulk is pretty runny stuff, so once you start laying it down you ideally want to continue until the tube is empty, although you can release the piston tab to stop the flow, lay the gun carefully over the joint, or on your cardboard piece. You'll work backwards, moving slowly backwards or sideways around the pool, squeezing in the caulk, carefully watching the flow to prevent overruns onto the topside of the deck or coping stone. Small drips and overruns can be quickly scraped up or mopped up, keep a wet sponge handy. 

Here's a great video of a Bowling Green, Virginia company Seastead Building And Remodeling LLC doing a pool caulking job, using Vulkem SSL pool caulk.




Thanks for Reading! (and watching)

Mark Garcia