Home Improvement Exterior Remodel Doors & Windows

How to Caulk a Window

Keep the home properly insulated and draft-free by caulking the windows.

Timothy Dale

Updated on 01/17/23

Reviewed by

Johnathan Brewer

How to caulk a window — BanksPhotos / Getty Images

Project Overview

Working Time: 1 - 2 hrs
Total Time: 1 hr, 30 mins - 3 hrs

Skill Level: Beginner
Estimated Cost: $$10 to $30

Leaks, gaps, and cracks between the window frame and the walls can increase energy bills, reduce home comfort, and leave the home vulnerable to air, moisture, and insect infestations. The most common solution to this problem is to use caulk to seal the gaps and cracks around the window frame to prevent warm air from escaping in the winter, cool air from escaping in the summer, and moisture from entering the home throughout the year.

Caulk is a flexible material with the consistency of thick glue. It comes in a tube and can be applied with a caulking gun, which squeezes the caulk out through a hole in the applicator tip, allowing the user to apply the caulk in long, straight lines. Depending on the type, it can be used indoors, outdoors, and in high-moisture locations, like kitchens or bathrooms. To learn more about caulking and to find out how to caulk a window, follow the steps below.

Before You Begin

It's necessary to figure out what type of caulk you need before starting this project. Consider where the caulk will be applied, what type of conditions it will be subjected to, and whether you want to be able to paint over the caulk bead or not. Common types of caulking include acrylic latex caulk, siliconized latex caulk, silicone caulk, and polyurethane caulk.

Acrylic latex caulk can be painted, making it a good option for interior use in areas that are not high in moisture. However, due to the proximity of most windows to the outdoors, acrylic latex should not be used to seal a window. This is because acrylic latex caulk doesn't flex or expand in response to temperature changes, so seasonal temperature shifts can crack the caulk. Additionally, moisture reduces the durability of this product.
Siliconized latex caulk can also be painted over, but you can use this caulk in high-moisture areas, like kitchens or bathrooms. It also responds better to temperatures, exhibiting more flexibility than acrylic latex. Though, it may still suffer when exposed to rough outdoor weather, like heavy rain, sleet, ice, and snow.
Silicone caulk is one of the most durable caulks available, allowing it to be used in a wide variety of applications. This type of caulk is known for its high water resistance, though it's worth noting that silicone caulk can have problems adhering to wood and it shouldn't be painted.

Polyurethane caulk is one of the best choices for sealing window gaps because it adheres to a range of materials, including metal, wood, and glass. However, if you are applying this caulk outdoors, make sure to paint the caulk because polyurethane caulk is not resistant to UV radiation. Extended exposure to the sun can cause the caulk to break down.

Equipment / Tools

Putty knife
Utility knife
Cloth
Bucket
Caulking gun
Caulk smoothing tool

Materials

Window caulk

Remove Old Caulk

To start this project, you need to use a putty knife to remove the old caulk surrounding the window. If you are having difficulty pulling the caulk out of the gap with just a putty knife, considering cutting through the caulk with a utility knife so that it can be removed from the window frame.

It isn't recommended to apply new caulk over existing caulk because the old, cracked, and hardened caulk will act as a barrier, preventing the new caulk from adhering properly to the window frame and wall.
Prepare the Area

After removing most of the old caulk, use the putting knife or utility knife to scrape off any remaining bits of caulk or old paint. Inspect and repair any damage on or around the window. If the windowframe and wall are in good condition, use a cloth and a bucket of warm, soapy water to clean the area.
Load the Caulk Gun

While you are waiting for the newly cleaned window frame and wall to dry, place the tube of caulk into the caulk gun. Squeeze the handle on the caulk gun just enough to move the plunger cup securely against the end of the tube.

With the tube held in place, use your utility knife to cut the applicator tip at a 45 degree angle, about 0.25 inches back from the tip. After cutting the hole in the end of the applicator, use a long nail to pierce the seal inside the tube.
Apply Caulk to the Window

Don't try to run a continuous bead the entire length or width of the window. Instead, start at one end and squeeze the handle of the caulk gun to run a uniform bead of caulk to the middle of the seam. Then start at the opposite end and run the bead of caulk along the seam until it meets the first bead in the middle.

Make sure to press the tip firmly against the seam as you apply the caulk, so that it fills the gap. Repeat this process on all four sides of the window to seal the opening between the window frame and the wall.
Smooth Over the Caulk

Once you have applied beads of caulk to all four sides of the window you need to smooth the caulk in a process known as tooling. You can use a popsicle stick, your finger, a thin rag, or you can purchase a caulk smoothing tool to complete this process.

Regardless of your tool of choice, to smooth over the caulk, you simply need to run the tool or your finger over the bead of caulk. Drag it with light pressure to smooth the caulk into the joint. This helps to prevent the caulk from slipping out of the seam or drying unevenly.
Allow the Caulk to Dry

After application you will need to allow the caulk to dry for at least 24 hours. Check the manufactuer's directions for the drying and curing time for a more detailed breakdown on exactly how long the caulk will require to fully cure.

How Often to Replace Window Caulking

Window caulking is made to last, so you won't have to worry about your beads of caulk failing just a few weeks after applying it to the windows. However, many people believe that once installed, caulking never needs to be inspected or replaced. Unfortunately, this isn't the case. In a brand-new house, you may need to replace the caulking around the windows and doors after just one year because the house tends to settle during the first year, impacting the integrity of the caulking.

In an older house, the structure has already settled, so the caulking can last much longer. You should inspect the caulking about once every year or two and plan to replace the caulk about once every five to 10 years, depending on the condition of the caulk. If you notice drafts in your home or that your energy bills have spiked, this is a sign to replace the caulk around your windows and doors.

When you are replacing caulk, make sure to first remove the old caulk. In most cases, if you apply new caulk over old caulk that has hardened and cracked, the new caulk will not be able to form a clean seal or adhere properly to the window frame, wall, or old caulk bead. Instead, clean out the old caulk and apply a new bead, using two hands to control the caulking gun for accurate application.

Don't try to run a continuous bead from the top to the bottom or from one side to the other because the position and angle of your hands will change as you move. It's better to start at one end and run the bead to the middle of the seam and stop, then start a new bead at the other end and run the caulk until it meets the first bead in the middle.

However, if you have shaky hands or you are unsure of your accuracy, you can use painter's tape to tape off the seams. Leave the gap that you want to caulk and apply painter's tape on either side of the gap to prevent your bead from going astray.