top of page
  • Writer's pictureDunsmuir Hardware

How to Caulk a Waterproof & Airtight Seal

Caulk and sealant are an indispensable part of any homeowner’s toolbox. Whether you’re using them for waterproofing, or to keep your home airtight and energy-efficient, knowing how to properly apply them is a must so that they work effectively. These sealing and caulking tips will help your project be more successful.

Step 1: Prepare the Surface

Good surface and joint preparation will help you complete a professional-looking and long-lasting caulking or sealant job. Whether replacing old caulk or sealing a new joint for the first time, it is important to remember to clean out the old caulk from the surfaces, cracks, and crevices of the areas where you will be applying the new caulk. Traces of dirt, paint, oil and old caulk left behind will only lead to problems later on.

Use a putty knife, painter's 5-in-1 tool, or another similar tool to remove any old caulk in the joint. A heat gun can be used to soften old caulk and loosen paint to make removal easier. You can use a chemical indoor/outdoor caulk remover to remove all types of old caulk as well. The surface needs to be completely free of the old caulk, peeling paint, weathered wood fibers, grease, oil, wax, dirt, rust, frost, moisture, etc. A wire brush works well to remove contaminants, and a drill-mounted wire wheel is often the best answer for cleaning dirty, unsound concrete. To remove some contaminants (like oil or grease) it may be necessary to wipe the joint down with a solvent-laden rag (letting the solvent completely evaporate before caulking). Remember, the best caulk in the world won't work if it is applied to a dirty or imperfect surface.


If the joint or crack to be sealed is 1/4" wide or wider, it is best to install a foam backer rod in the joint before applying the caulk or sealant. This will give you better results and save you money. Backer rods are generally cheaper than a good quality caulking compound, and most of the joints can be filled with the backer rod before the actual caulk or sealant is installed. It also provides better caulk or sealant adhesion in the crack or gap.

Step 2: Watch the Weather

Weather can affect the long-term performance of caulks and sealants, so it's important to keep it in mind when you are planning on applying caulk or sealant outside. The best conditions include temperatures between 50 and 90 degrees Fahrenheit. When the contact area is too cold, the surface will contract and the joints will expand. Temperatures that are too hot will cause the surface to expand, which will make the joint contract. High temperatures can also make the caulk blister which causes poor adhesion.

Weather can affect the size of the joint at the time of caulking, the ability of the caulk to "wet" the surfaces of the joint for good adhesion, and the ability of the caulk to properly cure and develop its ideal physical properties.

Don’t apply caulk or sealant when it’s raining or snowing. Even if the weather is ideal the day you plan to work on the project, but it has recently rained, it may be necessary to wait one to three days to allow the surfaces to dry out or warm up adequately. Also, avoid applying sealants or caulk if the weather is expected to turn bad shortly after you’re planning on applying it.

Step 3: Cut the Nozzle Tip

Embossed markings on a caulk/sealant nozzle determine the size of the bead that can be dispensed when the nozzle is cut at each marking. By cutting the nozzle at these different measurements, you can form a caulking bead to match your joint size. Using a utility knife, cut the nozzle at a 45-degree angle, and place it in a caulking gun. You're ready to begin.


Note that most cartridges have an internal foil patch at the base of the nozzle that needs to be punctured with a nail or other slender sharp object).

Before you actually start to caulk, do some test caulking on a newspaper or paper towel to get a better feel for how the product dispenses. It is especially important to get the feel of keeping the caulking gun moving smoothly as you complete one stroke of the trigger and begin the next stroke.

Step 4: Apply a Bead of Caulk

As you begin applying caulk or sealant, hold the caulking gun at a 45-degree angle parallel to the joint being filled. Position the nozzle opening so that it forces sealant onto the joint surfaces. As you finish applying each bead of sealant, release the trigger and pull back on the caulking gun rod to stop the flow of caulk and relieve the pressure inside the tube. Releasing the trigger alone will not stop the caulk from flowing out of the nozzle. Only apply about 2 to 3’ of caulk at a time. This will allow you enough time to get it tooled before it begins to skin over and harden (which can make tooling very difficult or even impossible).

Be sure to pull the caulking tube nozzle along the joint rather than pushing it. Pulling the nozzle allows for a smooth application over any obstructions on the surface being caulked; while pushing the nozzle can lead to more hang-ups and sudden breaks in the flow of the caulk which can lead to messy blobs. Keep in mind, if you create an imperfect section of a bead, you can always scrape it out right away and start over.

Step 5: Tooling Your Caulk

Tooling the bead of caulk ensures good adhesion and good-looking results. Tooling is the process of smoothing over the entire length of the previously applied bead of caulk. This process smoothes out the thick caulk and forces it into the joint to establish good adhesion. Depending on the type of caulk used, tooling can be done with a latex glove-covered finger (wetted with some water or solvent) or with your bare skin, or with various tools like a piece of wood shaped like a spoon or a foam paintbrush. To avoid removing to much sealant from the joint and wasting caulk, it is important to avoid scraping an excessive amount of caulk out of the joint during tooling. Keep in mind that dried caulk is much more difficult to clean than wet caulk. Keep rags readily available to clean up any spills or problem areas right away.


Masking tape can be helpful in creating a smooth line with less mess. Just make sure the tape is removed immediately after tooling is complete and before the caulk skins over so that it will pull away cleanly and leave a smooth, even line.

That’s it! You’re ready to caulk and seal.

Project Shopping List

Here’s what you’ll need to complete this project successfully.

  • Putty knife, painter's 5-in-1 tool, or another similar tool

  • Heat gun (optional)

  • Chemical indoor/outdoor caulk remover (optional)

  • Wire brush

  • Drill-mounted wire wheel

  • Solvent (for oil stain removal)

  • Rag

  • Foam backer rod

  • Caulk or sealant

  • Utility knife

  • Newspaper

  • Latex gloves

  • Spoon

  • Foam paintbrush

  • Masking tape

Recent Posts

See All


Post: Blog2_Post
bottom of page