7 Most Common Caulking Mistakes That Could Derail Your Project

Updated: Apr. 14, 2024

When the time comes for you to pick up that caulking gun and seal a shower or lay a new bead on an exterior siding seam, watch out for these aggravating pitfalls.

Failing to Prep

The first common mistake happens before you even open the caulk tube.

Without proper surface preparation, your new caulk will not last. As tempting as it is to quickly lay a new bead and forget about it, you need to ensure the surface is dry, clean and sound before applying caulk.

Completely remove the old caulk, flaking paint or crumbling grout. Repair any surface damage, wipe the area clean and then lay the new bead. “Be sure it’s as clean as possible and then completely dry to ensure a proper seal once caulking is laid,” Fabry says.

This is especially important when recaulking the seam between a bathtub and tile surround. Remove all old caulk before applying a new bead.

Overcutting the Tube Nozzle

When you open a tube of caulk, the tapered tip on each tube allows you to custom-size the opening for your specific job.

Many people cut the tip and start caulking without regard for the width of the crack they plan to seal. This can result in too much material on the surface, poor adhesion and/or a sticky mess. Fabry suggests starting small and then adjusting the opening if needed.

Cut your tip slightly narrower than the opening and use pressure and speed to adjust the width of the bead. I use a utility knife to cut the nozzle rather than the included cutting blade on most caulking guns. A utility blade allows for more accuracy and a cleaner cut.

Not Using Backing

Caulking openings wider than one-quarter inch or more than one-half inch deep requires backing material such as foam rope. Pumping a huge crack full of caulk is expensive and affects product performance. Caulk that is too thick will crack and shrink when it dries.

Backing material optimizes the thickness of the bead and allows for the best cosmetic finish. Tightly pack backing material into the crack, making sure it’s just below the surface. Then run your bead of caulk over it for great results that will last.

Not Practicing First

Many people charge right in, applying material immediately to the task at hand. Creating the best-looking, most effective bead of caulk takes some skill. Fabry suggests practicing first on a piece of scrap wood or trim. “It’s worth it to take a couple of practice swipes to get the hang of it first,” he says. I always warm up before caulking a highly visible area.

A consistent bead is key to success, so plan to avoid any sudden stops during application. Anticipate spots where you may run out of space for the caulk gun and begin rather than finish in corners. Do your best to keep pressure, speed and angle consistent. Avoiding sudden stops keeps your carefully crafted bead from becoming a mess.

Tooling Incorrectly

Don’t miss the final critical step in the process: Tooling. “After laying down a line of caulk, you have to spread it either with your finger or with a caulking finishing tool,” Fabry says.

Most of the time, the only additional caulking tools required are a fingertip, some water to dip it in and some paper towels. However, caulk finishing tools are available to make the job easier and less messy.

Either way, smoothing the bead with light, steady pressure does two thingsā€”it forces the caulk firmly against both surfaces and creates a clean, tidy appearance. Don’t overwork the bead, or you’ll risk removing too much product.

You’ll also want to work quickly before the caulk begins to dry. When I caulk bathtubs I complete one section at a time to avoid the silicone skinning over before I have a chance to tool it smooth.

Using the Wrong Caulk

Choosing the right caulk for the job is crucial. “Make sure you do your research and read labels very carefully,” Fabry says. If you are planning to paint, make sure the caulk is clearly labeled as ‘paintable’. If you are caulking a shower, make sure the product is 100% silicone and can withstand constant water exposure.

You may notice your mistake right away, or it may take time to materialize. Silicone caulk will immediately shed paint, but if you apply acrylic caulk around a tub it will look good at first. However, with use it will “turn slimy when wet, its integrity will degrade, and you will have leak issues,” Fabry says.

Extreme Temperatures

Follow the manufacturer’s instructions for storage and application temperatures for best results. If you grab a tube of acrylic caulk that sat in freezing temperatures overnight, it will be difficult to apply until it reaches room temperature and flows easily. Likewise, caulk that has sat in the hot sun will be runny and will not apply well to vertical surfaces.

“Temperature absolutely matters,” Fabry says, so pay close attention to the manufacturer’s recommendations. If temperatures are too warm or cold, caulking will not cure correctly.

“Your hard work will have been in vain,” Fabry says, “and will need to be redone when the temperature is in the recommended window.”

About the Expert

Matthew Fabry is a licensed contractor and owner of Roots Construction, a homebuilding and remodeling company in Easthampton, Massachusetts. He has over twenty years in the construction industry.