What Is Pool Mastic? And How to Use It

You may already be familiar with more standard chemicals and tools like chlorine and muriatic acid. But one item you may not have heard of is pool mastic. So, what is pool mastic, and how do you use it?

In this article, I’ll explain everything there is to know about pool mastic so that you can use this to replace the mastic in your swimming pool when needed. Let’s get into it.

Main Takeaways

• Pool mastic, also called pool caulk or sealant, seals the area between the coping and the decking.
• Mastic is used to waterproof, allow for movement, and prevent debris from falling in the gap.
• Signs that signify it is time to replace the pool mastic include: cracks in the decking, peeling mastic, tiles falling off, separation between decking and coping, and deck heaving.
• To replace pool mastic, you’ll need to remove the old mastic, prep the area, insert a foam backer rod, apply the pool mastic, smooth it out, and allow it to cure.

What Is Pool Mastic?

Pool mastic, more commonly known as pool caulk or sealant, seals the pool so that the water from the pool doesn’t seep into the area surrounding the pool. If you have an inground pool, you will have coping around the pool, which not only makes your pool look more aesthetically pleasing but also helps with water splashing out of the pool and into the yard or deck. And this is where pool mastic comes in! The pool mastic seals the area between the coping and the pool deck, keeping your deck dry. Beyond that, it has multiple other uses.

What Is Pool Mastic Used for?

Pool mastic is vital to maintain your inground pool’s structural integrity and longevity by sealing the joint between the coping and pool deck. This joint is necessary because the coping and deck are constructed from different materials that expand and contract at different rates. Without proper sealing with mastic, this joint can cause severe and costly damage down the line.

Waterproofing

Pool owners mainly use pool mastic to keep the water out. Without mastic, water will seep into this expansion joint, which can cause soil movement, cracks, freeze damage, and more. All of which can lead to damage to your deck and coping. In other words, mastic gives your coping and deck the space to expand and contract as necessary.

Movement

Besides waterproofing, you can also use mastic to allow for movement. As temperatures fluctuate, your coping and deck will expand and contract. Pool mastic is flexible and allows for this movement, preventing your precious pool deck or coping from cracking.

Preventing Debris

Finally, if you leave your expansion joint unsealed, dirt, debris, and even seeds may lodge in this joint, which may lead to weed growth and debris collection. In particular, weeds can cause damage by pushing the joint apart. The pool mastic seals this joint, preventing issues from arising by keeping the area clean.

Signs That You Should Replace Your Pool Mastic

Pool mastic doesn’t last forever. So, when do you know it’s time to replace the mastic so that the expansion joint remains sealed and safe from the pool water and elements? Here are some of the telltale signs to look out for.

Cracks in the Decking

As you know by now, mastic is an important pool material that allows decking and coping to expand and contract. One sign that your mastic is older and not doing its job properly is if you notice cracks in your decking. This means that the mastic is struggling to absorb the movement between the pool and the deck effectively. These cracks may be minor at first, but it’s absolutely important that you deal with the issue right away before this becomes a more expensive fix.

Peeling Mastic

If the pool mastic is old, you may notice the mastic peeling away or perhaps even developing cracks. This can be caused by UV rays, pool chemicals, and even the weather. But, over time, if you notice the mastic beginning to peel, replace it as soon as possible, as it is quickly losing its effectiveness in sealing the expansion joint.

Tiles Falling Off

There are several different reasons why your pool tiles may be falling off the pool, but one potential issue could be underlying issues with the pool mastic. If it’s time to replace the mastic, it might not be able to prevent the concrete from moving around, leading to falling tiles. Remember that this is not the only reason your tiles may be falling off the pool, so make sure you troubleshoot thoroughly to determine the actual cause.

Separation Between Decking and Coping

Have you noticed that the decking and coping are starting to separate? This means the mastic is not properly bonded. Even if it’s a tiny gap, you’ve got to fix this as soon as possible by replacing the pool mastic to seal the gap once again.

Deck Heaving

While deck heaving doesn’t necessarily mean there is an issue with the pool mastic, it can lead to issues down the line. Deck heaving refers to when the decking shifts and rises above the level of the pool, which can be caused by soil expansion, erosion, and extreme temperatures. When this happens, the mastic between the coping and decking may no longer be holding firm, so check to ensure everything is still sealed.

Step-by-Step Process: How to Replace Pool Mastic

So, you’ve determined it’s time to replace the pool mastic. Don’t worry; this is not as difficult of a task as it may seem. If you have the right tools and DIY knowledge at hand, you should be able to replace it with relative ease.

Step One: Remove the Old Mastic

First, you’ll need to remove the old mastic before applying the new pool mastic. To remove it, use a putty knife to scrape away the mastic from the expansion joint. Make sure to get rid of all the remnants.

Step Two: Prep the Area

Once the old mastic is gone, clean the joint thoroughly to remove dust, mold, or debris. Use a damp cloth to clean and prep the area. At this point, you should also check the joint for any damage or cracks that may need repairing before you apply the new mastic. Ensure the joint is bone dry before proceeding to the next step.

Step Three: Insert a Foam Backer Rod (Optional)

The joint should be around the same depth and width. If it isn’t, insert a foam backer rod. The backer rod should fit snugly and leave enough room on the top for the new mastic.

Step Four: Apply the Pool Mastic

Use a caulking gun to carefully and evenly apply the new mastic. Follow the manufacturer’s instructions. Start at one end of the joint and work steadily to avoid gaps or air pockets.

Step Five: Smooth It Out

Probably the most difficult part about applying mastic is ensuring it looks nice and neat. Use a trowel or your finger to smooth the surface to create a neat finish. The mastic should be level with or slightly above the surface of the coping and decking.

Step Six: Cure the Mastic

Let the mastic cure according to the manufacturer’s instructions, which is generally at least 24 hours. Make sure no one enters the pool area around this time.

How Often to Replace Pool Mastic

Generally, you should replace the pool mastic every 1 to 10 years. Big range, I know! However, the lifespan depends on various factors, including climate and pool usage. Exposure to harsh sunlight, pool chemicals, and temperature fluctuations can cause the mastic to degrade over time, leading to cracks, peeling, and loss of flexibility.

While there is no hard and fast rule on how often you should replace the pool mastic, keep an eye on the warning signs listed above that indicate it is time to replace the mastic. I recommend checking your pool monthly for any signs of the mastic failing.

Frequently Asked Questions

Can I replace pool mastic myself?

Yes, absolutely! You can replace pool mastic yourself, especially if you have some DIY knowledge at hand. To replace the pool mastic, follow my step-by-step process highlighted above, which includes removing the old mastic, cleaning the expansion joint, and applying the new pool mastic.

How thick should pool mastic be?

Apply the pool mastic to a thickness of around 1/4 to 1/2 inch, depending on the width of the expansion joint.

Seal the Gap

Although small, pool mastic plays an important role in protecting your pool. Who would have thought something so small and seemingly insignificant could help waterproof, allow for ground movement, and prevent debris from falling in the gap between the coping and the decking? While you won’t need to replace it very often, keep an eye on the mastic as well as other telltale signs that signify it is time to replace it before it’s too late.

Any more questions about mastic? Let me know!