How To Seal Gap Between Window And Brick Wall: 6 Steps

A gap between a brick wall and the windows can allow outside air and moisture to get inside, resulting in damage and loss of heat or cooled air. 

Thankfully, you can seal this gap on your own with relatively low-cost materials such as caulk, expanding foam, closed-cell backer rod, and more.

How To Seal The Gap Between A Window And A Brick Wall

Sealing a gap between the brick wall and window is essential for keeping out bugs, moisture, and other nuisances. 

Follow these easy steps to make your home more energy-efficient.

What You’ll Need

  • Cleaning solution
  • Gap filler of your choice
  • Exterior caulk
  • Caulking gun with thumb release
  • Cleaning rags, brush, towels, sponge
  • Mineral spirits
  • Measurement tool
  • Water
  • Putty knife
  • Rubber gloves
  • Caulk removal and application tools
  • Mortar and application tools
  • Wide masking tape
  • Lighter and candle
  • Ladder 

1. Choose A Gap Filler

There are several fillers you can use to seal the gap between a window and a brick wall, but not all work for all situations. 

Generally, caulk is recommended for gaps that are 1/4-inch or smaller. Expanding foam combined with a backer rod works best for larger openings. 

Caulk is used for finishing seams as well. 

Measure the gap area to determine the materials that work best for you. 

Find the largest and smallest parts of the gap to pick a material that works in all areas surrounding the window.

MaterialGap Size Fitting
Caulk (Silicone or Polyurethane)1/4-inch or less
Low Expansion Expanding FoamExpands up to 30 times its liquid size
Adhesive StripsFrom 1/16-inch to 1 1/2-inch 
Closed-Cell Backer RodFrom 1/4-inch to 2-inch

Any materials that you use to fill in the gap should have the following requirements:

  • Formulated for exterior use. 
    • For example, it can deal with UV light, water, and temperature changes.
  • Compatible for use on different types of material. 
    • For example, it should work with both brick and aluminum window frames.

Exterior Caulk

Windows can be caulked to brick, but check the caulk label to make sure it is formulated for exterior use. 

Silicone or polyurethane caulk is often used for sealing gaps, but it may need replacement over time if it cracks or degrades. In addition to filling the gaps, caulk is also used for finishing. 

Clear caulk works well with mixed materials and colors that are joined.

Use a caulking gun with a thumb release to allow you more precise control in stopping the sealant from flowing. This will help you get a consistent caulk bead.

Expanding Foam

This kind of foam comes in a pressurized can and is best for filling large gaps around window frames

As it settles into a gap, it will expand and fill in all of the spaces, insulating the window and creating a moisture barrier. 

Typically, expanding foam is concealed with an exterior trim after filling the gap. This is why you should apply it sparingly to avoid overfilling and bulging.  

Check the product label for expansion specifics. High expansion foam can expand up to 300 times and could warp the frame of your window. Opt for low expansion foam that expands up to 30 times its liquid size.

Adhesive Strips

There are two kinds of adhesive window gap filler strips:

  • Foam: An adhesive foam window strip is used much like expanding foam. It is lightweight and flexible, yet durable and water-resistant, available in various widths and thicknesses. 
    • The adhesive that comes with this material works well with brick walls. 
    • Keep in mind that it may not fill in minuscule gaps, like expanding foam or caulk.
  • Rubber: Rubber is naturally waterproof; it is a great option for closing small gaps and keeping water and drafts out. 
    • However, it does not fill in small irregularities like expanding foam or caulk will do, so it works best in tighter fitting situations. 
    • It may also shrink or crack when exposed to heat.

Both strip types work well if applied to the window frame during window installation. It can be difficult to line these up perfectly once the window is already in place.

Closed-Cell Backer Rod

This material is used in conjunction with caulk or expanding foam when there is a large, deep, or wide gap. 

It is non-porous and compressible, offering a thick internal pressure and reducing the amount of other sealants used. It will force and press on the other materials to ensure that it touches and adheres to the surrounding surfaces, creating a stable “core” in the gap.

This product comes in various sizes ranging from 1/4-inch to 2-inches. Choose a backer rod that is approximately 30% larger than the width of the gap, but not less than 10% of the gap. 

2. Check The Weather

Ideally, you should wait to seal gaps and windows when there is no forecast of precipitation for several days. This helps you avoid trapped moisture or rain affecting your sealant materials negatively.

3. Prepare The Window And Gap Area

If necessary, remove any old caulk with caulk removal tools.

Repair any cracked or broken bricks with mortar. Allow the mortar to dry and cure before proceeding.

Keep in mind that brick is a porous material. You may see weep holes, and gaps between some bricks, which are a building code requirement to allow water to drain out of exterior brick walls. 

Do not fill these weep holes with mortar. These are located in the bottom row of bricks above the flashing.

Brush away dust, spiderwebs, and debris. 

Use a mild cleanser, such as vinegar, and spray down surfaces to remove mildew and grime. If desired, you can use white mineral spirits to remove oil or grease. Wipe down with clean water. 

Every affected surface should be dry before sealing the gap.

To keep the area surrounding the window free from sealing materials, use masking tape to mark off the area around the frame.

If you are using a ladder, you should have another person spotting you for your safety. The ground should offer a firm and stable surface for the ladder as well.

4. Fill The Gap

Apply your sealing material(s) according to labeling instructions. 

Ideally, you want all gaps filled with a material capable of filling the depth and width between the window and the surrounding brick, along all edges, corners, and supports. 

Work from the top and down. Allow drying times, if necessary for chosen fillers.

If you find your gap is slightly larger than 1/4-inch, and you wish to use caulk because other materials will not fit, you can do the following:

  1. Fill the gap with a bead, or line, of caulk deep inside the depths of the gap. 
  2. Allow it to fully cure. 
  3. Then, put on another layer, repeating, until you have filled the gap up to the surface point.
  4. The final top surface line of the caulk should be applied smoothly for a uniform appearance. 

5. Check The Gap

You can check the gap to see if there is any air movement by trying the following:

  • Candle: If it is not a breezy day, you can light a candle and hold it up near the seams. If the flame vibrates, air may be leaking from that spot. 
    • Recaulk as needed.
  • Water: Pour water along the cured seams. If you see bubbles or the water looks like it moves differently, there may be air. 
    • Allow the area to fully dry before adding more caulk to avoid trapping moisture inside.
  • Visual: Inspect the outer caulk layer up close. If you see any dark lines or spots that are inconsistent with the rest of the caulk, there may be a weak spot. 
    • Add another layer of caulk, making it thicker in width if necessary.

6. Trim And Finish With Caulk 

Window trims are used to cover filled-in gaps. Apply smooth and even caulk around all seams to create a waterproof seal and finished look. 

When connecting two surfaces with caulk, one may be bumpier than the other. Draw the caulk gun’s tip along the smoother surface to avoid bumps in your line, while allowing the material to settle onto the bumpy surfaces, connecting the seam. 

Conversely, you can use caulking application tools to ensure a finished smooth line. Again, you’ll want the edge of the caulking tool to rest on the smooth surface to avoid a bumpy motion.

Do not caulk around any moving parts of the window or the weep holes. Weep holes can be found on the bottom edge of storm windows which drain water away from the window sills.

If you get any caulk on the window glass, use a damp cloth to wipe it off immediately. If it has dried, carefully scrape it off with a putty knife. 

Remove the masking tape so it does not permanently adhere to the caulk. Let the caulk dry and cure according to the product’s instructions.

Benefits Of Sealing Window Gaps

Sealed window gaps offer a variety of benefits, including:

  • Prevention of drafts, keeping the home energy efficient
  • Energy efficiency reduces utility costs
  • Protection from moisture buildup and potential rot, mold, or mildew
  • Sound barrier to external noises
  • Keeps pests and insects out
  • Window longevity
  • Decreased risk for costly repair work

Key Takeaways

We hope this article has helped you learn how to fill exterior gaps around window frames and a brick wall on your own.

By cleaning the gap and then sealing it with expanding materials and caulk, you’ll create a barrier and protective seam.

The steps above will help you maintain and promote the longevity of your windows for continued years of enjoyment.

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