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Reasons Why Caulk Cracks: Tips to Prevent Cracks in Caulk

Matt By Matt January 4, 2022

Have you ever wondered why caulk cracks? Maybe you've noticed a crack or two around your home and wondered what caused them. This article will provide several reasons why caulk cracks. We'll also provide caulk replacement recommendations, cleaning tips, and suggestions for future caulk removal. It can save you money and prevent frustration if you know the causes and how to repair cracked caulk.

Reasons Caulk Cracks

Here are several of the most common reasons that caulk cracks.

Reason #1: Using the Wrong Type of Caulk Can Cause Cracks

Caulk comes in two types: flexible (such as elastomeric sealants and silicone caulk) and rigid (such as acrylic latex caulk).

Flexible caulk moves with the material to which it's bonded.

Rigid caulk doesn't flex well and cracks as the materials it's bonded to expands.

How can you tell if you need flexible or rigid caulk?

Well, it depends. The type of interior caulking you need depends on where you live. Even though indoor temperatures rarely change throughout the year, humidity levels do change and vary based on location. In the north, the winter months decrease indoor humidity. As the humidity level drops, the water level in caulked surfaces (for example, crown molding and trim) decreases, and the wood tends to contract. As the substrate contracts, the caulk expands, which generally causes cracks if the caulk is not flexible enough to adapt to the movement changes.

External caulking typically requires a more flexible caulk for both expansion and weatherproofing. It is not recommended to use a pure acrylic latex caulk on exterior applications like doors, windows, and masonry. For exterior applications, we usually recommend avoiding acrylic caulk, and buying a more flexible caulk, such as an elastomeric or silicone sealant for use on exterior applications.

So, the answer depends on where you plan to caulk. If you use the wrong caulk for the job, you will most likely get cracks.

Reason #2: Too Little Caulk in Your Caulk Bead Causes Cracks

Creating a caulk bead with too little caulk can result in cracks and gaps.

If you caulk too quickly, you may not have enough caulk in your caulk bead. It's easy to move the caulking gun too quickly, resulting in a thin bead. So the pro-tip is to move the caulk gun (or squeeze tube) slowly to avoid cracks. You don't want too much, but you don't want too little either.

You can also end up with too little caulk in your bead if you wipe too much off when smoothing it out. It's easy to accidentally wipe away too much caulk between a joint and drywall when using a putty knife. This is why we recommend smoothing out caulk beads with a soapy finger because you can feel how much pressure you're applying.

Another way to end up with too little caulk in your bead is if you apply "just enough," but the caulk shrinks as it cures. Some caulk shrinks by as much as 25% before curing, regardless of humidity or temperature. Make sure you check the label to see if the caulk shrinks before curing or not. If the label says it shrinks, then use a little more to prevent premature cracking.

Reason #3: Forgetting to Use a Foam Backer Rod Causes Cracks

If necessary, use a backer rod before you caulk.

A backer rod is designed to be used before caulking and helps prevent caulk slump which causes cracks. Most backer rods are made of a polyethylene closed-cell foam material and they resemble floppy pool noodles (but much smaller). We recommend using a backer rod before caulking large gaps.

Usually the caulk manufacturer sets gap size limits. If you go beyond those limits, then a backer rod is recommended. It's really easy to use a foam backer rod. Just insert it into the gap and then dispense the caulk on top of the rod.Backer rods prevent caulk from slumping, which could cause cracks and gaps.

Backer rods also add a little insulation to the area that you're caulking. It's not much, but it's better than nothing.

Reason #4: Old Caulk Usually Cracks

Old caulk may also crack over time. With age, caulk develops cracks in the same way that our faces develop wrinkles. When the caulk has reached the end of its useful life, it's probably time to replace it.

Be sure not to cover up the existing caulk with the new caulk. You might get away with it if you use silicone caulk, but it's not the best option. It's usually very easy to remove old caulk inside a house. All you need is a utility knife with a sharp blade.

When it comes to removing exterior caulk, it requires some finesse. In many exterior caulking applications, the surface is porous, so the caulk has really penetrated the brickwork, wood, and masonry over time. Using a utility knife and a pair of pliers, you should be able to remove most of the old caulk. Try mineral spirits if you didn't manage to remove all the caulk. Make sure to test the area first to make sure mineral spirits won't damage the substrate.

It is extremely important to follow several steps if you plan on covering the old caulking. Cleaning the old caulk well is critical, and if it is a painted surface, try to remove as much of the paint film as possible. It is also a good idea to clean up any joints that have caulk residue which may detract from giving you that professional look. To finish, dry the area with some rags or a paper towel.

Reason #5: Caulk that Fails to Cure Can Crack

Another way that caulk cracks is if it fails to cure. There are several reasons why your caulk might not cure.

If the caulk got wet during the cure process this might be one reason it failed. So before you caulk, check the weather and avoid caulking when it's going to rain or thunderstorm.

Another cause of cracks is if you start your interior painting or exterior painting before the caulk is cured. When you paint over caulk before the recommended time interval set by the manufacturer, it can prevent the caulk from completely curing and lead to cracks. Several caulks allow painting within a certain period after caulking but before cure, known as the "paint-ready period". As long as you follow the manufacturer's recommendations, you should be fine.

Best Tips to Avoid Cracking Caulk

That's all there is to it. Our best advice for avoiding cracks in your caulk is to pick the right type of caulk for the job, apply just enough based on the manufacturer's recommendations, go slow, use a backer rod if necessary, avoid caulking over old caulk, and let your caulk cure. You should be able to have caulk that lasts for a lifetime if you do those things.

Top Rated Exterior Caulk for Windows, Doors, & Brick: 3 Great Choices

Are you shopping for a new exterior caulk for windows, doors, & brick? Here are some of our favorites that we want to share. Also, if you need some help, then be sure to check out our detailed buying guide. It explains some of the important considerations when shopping for a exterior caulk for windows, doors, & brick.

Best Overall
OSI Quad
OSI QUAD is the best choice for most outdoor caulking jobs if you want superior performance. It comes highly recommended by the experts. OSI QUAD is the... Read More
Type of Caulk:Elastomeric Sealant
Durability:25 years
Fills Gaps:3/8 inches
Upgraded Gear is supported by its readers. We may earn an affiliate commission at no cost to you if you buy using a link on our site.
OSI Quad
Best for Large Gaps
Sascho Big Stretch
Sascho Big Stretch caulk is an elastomeric sealant with excellent indoor and outdoor performance. The caulk can fill gaps up to two inches wide without... Read More
Type of Caulk:Elastomeric Sealant
Fills Gaps:2 inches
Upgraded Gear is supported by its readers. We may earn an affiliate commission at no cost to you if you buy using a link on our site.
Sascho Big Stretch
Premium Choice
OSI Quad Max
OSI Quad Max is the professional caulking choice that offers superior adhesion to a wide variety of exterior surfaces and materials. Once it's dried, Quad... Read More
Type of Caulk:Elastomeric Sealant
Durability:15 years
Fills Gaps:5/8 inches
Upgraded Gear is supported by its readers. We may earn an affiliate commission at no cost to you if you buy using a link on our site.
OSI Quad Max
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