How to seal an exterior window

Of course, you can always hire professionals to seal the perimeter of your exterior windows, but imagine how satisfied you’ll feel after doing it yourself!

At Adfast, we firmly believe that with the right sealants and tools, sealing exterior windows is a project that anyone can accomplish.

We have prepared a short guide that will teach you how to properly seal windows in 7 steps.

Let’s get started!

Why is it important to seal exterior windows?

If you’re not feeling very motivated about sealing your exterior windows, keep in mind that well-sealed windows prevent a variety of problems.

Poorly sealed windows leave gaps for water to infiltrate between the window and siding, causing the siding to deteriorate more quickly.

These gaps also allow air flow into and out of the building, resulting in higher heating and air conditioning costs.

The condensation generated by this air flow can also cause the building structure and windows to deteriorate prematurely.

How to seal exterior windows properly

There are several steps you can take to seal windows like a professional.

Here is a 7-step procedure to follow for durable, efficient and aesthetically pleasing perimeter joints.

1 – Choose the right sealant

The first step is to choose the right sealant for your project. Neutral cure silicone adhesive sealants like the Adseal DWS 4580 Series are ideal for exterior window perimeter joints.

These products generally adhere very well to window frame and siding construction materials such as aluminum, glass, masonry, certain plastics, painted and unpainted metals, and other surfaces.

They also have excellent resistance to UV rays and will retain their flexibility and volume despite exposure to extreme temperature variations.

It’s important to note that silicone sealants cannot be painted. We therefore recommend selecting a product in a colour that complements your building with the help of our sealant colour matching tool.

2 – Remove old sealant

If you’re sealing the windows of a brand-new building, there’s no need to worry about removing old sealant. However, if you’re re-sealing a window, you’ll need to remove all traces of the old sealant before applying new product.

Old sealant can sometimes be very dry and difficult to remove. To make the task easier, you can try to soften it by heating it gently with a heat gun or welding torch.

Then, make an incision along the seal with a small utility knife (X-Acto or similar). You should be able to grasp the end of the sealant and pull it out in one piece.

Finally, use a flexible blade to scratch away any sealant that is still stuck on, taking care not to damage the surface.

3 – Clean the surface before sealing it

Once the old sealant has been removed, clean the surface with a cloth soaked in an alcohol-based cleaning product. The alcohol will act as a solvent, breaking down the last of the old sealant and making it less sticky and easier to wipe off.

Let the surface dry for at least 20 minutes, and take the opportunity to vacuum the gaps around the window to remove any last bits of old sealant that might have gotten lodged in during cleaning.

4 – Apply sealant primer

One of the secrets to a really strong seal is to apply sealant primer to the surface once it’s clean. This extra step will make the sealant adhere better to surfaces that are more difficult to stick to.

Always make sure the primer is compatible with your sealant and remember that primer should not be used as a replacement for preparing and cleaning the surface. Our Adseal sealants are compatible with Adseal Primer MK60095.

5 – Place backer rods if necessary

If the gap between your window frame and siding is wider than a quarter of an inch (about 6.5 mm), don’t hesitate to insert backer rods to bridge the gap before sealing it.

These small, compressible foam logs are used to control the depth of joints and help the sealant assume the optimal hourglass shape while filling any gaps and spaces that are too deep. They are available in multiple sizes.

6 – Apply the sealant

While it’s possible to make sealant joints without a gun, using a caulking gun is practically a necessity for large projects like sealing exterior windows.

Once you have your caulking gun, insert the sealant cartridge and cut the tip at a 45-degree angle. The closer you cut to the base of the cartridge, the wider the line of sealant will be.

Fore more information, watch this short tutorial video.

Start by applying a line of sealant somewhere that is not very visible, just in case you make a mistake. Hold the nozzle opening parallel to the exterior wall and apply a 2- to 3-foot line of sealant, maintaining consistent pressure on the trigger so the product spreads evenly.

It’s important to only apply 2 to 3 feet of sealant at a time, since you’ll need time to shape it before it starts to cure. If you make a mistake, quickly scrape off the freshly applied sealant, wipe the surface clean and start over.

7 – Shape the joints

You’ll need to shape your joints in order to remove any excess sealant and give them a professional look. An easy way to do this is to use a joint shaping tool that is wide enough to cover the gap the sealant is going to fill. The tool will help you obtain the ideal thickness and a 45-degree angle.

Position the tool at an angle that makes it easy to slide and move it gently in a straight line.

Adfast: your resource for professional sealing products and advice

Now you know how to seal exterior windows like a professional!

If you’d like more information about how to make perfect sealant joints or which products to use for best results, don’t hesitate to contact our specialists or check out the “News” section of our website.