How to Reseal Windows: A Step-by-Step Guide

Resealing windows means removing old, damaged sealant and applying fresh material around your window frame to stop cold air and water from getting in. It takes just a few hours, and all you need are some basic tools. If you're losing heat through poorly sealed windows, this guide walks you through the whole process.

So, how to reseal windows? Let’s find out!

Quick Answer: How to Reseal Windows?

To reseal windows, remove the old caulk, clean and dry the surface, fill large gaps with a foam backer rod if needed, and apply a fresh bead of high-quality silicone or polyurethane sealant around the frame. Smooth the sealant, allow it to cure fully, and replace worn weatherstripping if necessary. For double-pane windows with condensation between the glass panes, resealing is usually not possible, and the insulated glass unit typically needs replacement.

What Are Window Seals and Why Do They Fail?

Window seals are the layers of caulk and weatherstripping applied around the edges of your window, between the frame and the wall, and sometimes between the glass and frame.

Seal failure happens for a few reasons. First, Canadian winters are tough on sealants. Extreme temperatures cause your house to expand and contract, and over time, that movement can cause the material to crack. Secondly, UV exposure dries it out. Lastly, moisture can get underneath and loosen the bond. Most sealants last 5 to 10 years before they need replacing.

If we’re talking about broken window seals in double-glazed units, we’re talking about a different type of seal. More precisely, it has to do with the fact that the Insulated Glass Unit does not perform at its best. If you see fogging or condensation between the glass panes, the inert gas between the panes has escaped - that's exactly what it means that a double-glazed window's seal has failed. In this case, it’s rarely possible to reseal the windows. The best long-term solution is to replace the IGU.

Do Your Windows Need Resealing?

If you feel cold drafts or cold spots on the walls near your windows, and you’ve noticed increased energy bills, your windows’ seals might have to be replaced. If you notice visible cracks, peeling caulk, and moisture seeping in through the windows, there’s definitely a sealing issue. You should also look for water stains or mold at the base of the frame.

Tools and Materials You'll Need to Reseal Windows

Get these together before you start. Having the right tools saves you from stopping halfway through.

• Putty knife or scraper
• Utility knife
• Caulking gun
• Silicone sealant or polyurethane sealant
• Foam backer rod (for large gaps)
• Silicone remover
• Rubbing alcohol
• Masking tape
• A damp cloth and a dry cloth
• Sealant tool or a damp finger for smoothing
• Weatherstripping, if it needs to be replaced

For most Canadian homes, a high-quality silicone sealant is the go-to choice. It handles extreme temperatures, stays flexible, and has good weather resistance. But if you want to learn more about different types of caulk for windows, you can check our comprehensive guide on this topic.

How to Reseal Your Windows: Step-by-Step

The basic process for window resealing is: remove old sealant, clean the surface, apply new sealant, and smooth it off. For interior windows, you can use silicone caulk or acrylic latex caulk; both are resistant enough. It is recommended to reseal the interior of the window first to avoid trapping moisture.

Step 1: Remove the Old Sealant

Score along the old sealing material with your utility knife. Get the blade as close to the frame as you can without scratching it.

Use your putty knife to peel away the loosened material. Go slowly. Carefully scrape along both sides of the joint, the frame side and the wall side. Get as much of the old caulk out as you can.

For stubborn residue, apply silicone remover according to the product instructions. Let it sit, then scrape again.

If you notice any mold growth, it’s of the essence to remove it before applying a new caulk bead.

Step 2: Clean the Surface

Wipe the joint down with rubbing alcohol. This strips any grease, dust, or remaining residue. Then wipe again with a damp cloth and let the surface dry.

The surface must be bone dry before you apply anything. Moisture under your sealant causes seal failure within months.

Inspect the window for damage before applying the new sealant. If your window frame is cracked or warped, for example, applying a new caulk bead won’t help much. You may not even be able to achieve a smooth bead.

Step 3: Fill Large Gaps with Foam Backer Rod

If you notice large gaps, use a foam backer rod to fill them. This gives the sealant something to bond to on both sides.

Cut the rod with your utility knife and push it in with a blunt tool or your finger.

Step 4: Apply Masking Tape

Masking tape can be used around the edges of window frames to protect adjacent surfaces and help maintain straight lines when applying sealant.

Run masking tape on both sides of the joint, leaving a clean gap where the sealant will go. Press the edges of the tape down firmly so the sealant doesn't bleed underneath.

Step 5: Load Your Caulking Gun and Apply Sealant

Cut the nozzle of your sealant tube at a 45-degree angle. The opening should match the width of your joint, usually 6-8 mm.

Load the tube into your caulking gun. Squeeze the trigger until the sealant reaches the nozzle, then release pressure.

Hold the gun at 45 degrees to the joint. Start at one end and move in one direction without stopping. Apply a continuous bead over the full length of the joint. Move at a steady pace. If you move too slowly, you might apply too much caulking. If you move too quickly, you might leave some gaps behind. Either way, it’s easier to deal with excess sealant than with a patchy sealant bead.

Work one side at a time. Finish one wall section before moving to an adjacent side. Never apply caulk to movable parts, as this will seal the window shut.

Step 6: Smooth the Sealant

Wet your finger and run it along the bead in one stroke. Press gently to push the sealant into the joint. This creates the concave profile that sheds water and bonds to both surfaces.

Remove the masking tape while the sealant is still wet. Peel at a 45-degree angle and go slowly. If you wait until it cures, you risk pulling the sealant with it.

Wipe up any smears with a damp cloth.

Step 7: Let It Cure

Leave it alone. Most silicone sealants skin over in 30 to 60 minutes, but they take 24 hours to set properly. Keep the window closed and don't let rain hit the joint during that time.

Check out our guide to learn more about curing times for different types of caulk.

Step 8: Repeat the Process on the Outside

Sealing from the inside and from the outside is done for different purposes. Do both for the best results.

On the exterior, you're protecting your windows against rain, wind, and temperature shifts. Hybrid caulks are the most resistant for exterior windows.

Step 9: Replace Weatherstripping If Needed

Weatherstripping seals the moving parts of your window: the sash, the edges, the corners. Weatherstripping can last up to 10 years, but if you notice signs of wear and tear, replace it before that.

To replace it, open the window and pull the old strip out. Most weatherstripping types peel or pry away easily. Clean the channel with a damp cloth and let it dry. Cut your new weatherstripping to length with a utility knife. Press it firmly into the channel or peel and stick it in place, depending on the type.

Check our comprehensive guide to learn more about different weatherstripping types, so you can choose the best for your windows.

Common Caulking Issues

Sometimes, as careful as you were during application, the new caulk bead just didn't adhere properly. Or it starts to crack. How do you solve the issue? You’ll find some scenarios below.

Does the new caulk bead not stick properly?

Cause: It was applied on dirty, damp, or oily areas.

Solution: Remove the caulk bead. Clean the area again with rubbing alcohol. Make sure there’s no caulk residue left. The area must be completely dry before applying the new caulk.

Is the new caulk bead cracking or shrinking?

Cause: You may have used the wrong type of caulk or applied a new bead that’s too thin.

Solution: Remove the caulk bead to replace it. Use high-quality, flexible caulk and apply a smooth, even bead.

Messy or uneven application?

Cause: You may have applied too much caulk or didn’t manage to smooth it properly.

Solution: Remove the caulk bead to replace it. Use painter’s tape along the edges before applying caulk. Smooth it with a damp finger or tool. You can also use a putty knife, which is useful for smoothing out the sealant bead and scraping up any drips or spatters.

Does the new caulk bead take too long to dry?

Cause: There may be high humidity in the environment, or it’s a type of caulk that simply takes a long time to cure.

Solution: Make sure the area is ventilated properly and avoid exposure to moisture until fully cured.

DIY Resealing vs Calling a Professional

DIY resealing is a straightforward process for most windows. If you're comfortable on a ladder, can work with a caulking gun, and have a few hours, you can handle it.

Call professional glaziers when:

• The sealant failure is inside a double-glazed window unit (between the window panes).
• The window frame itself is rotting or cracked.
• The windows are too high.
• The window is large, fixed, and difficult to reach safely.

Window resealing done by a professional costs more but guarantees a durable and airtight seal, and the work usually comes with a warranty.

Mistakes to Avoid when Resealing Windows

• Don’t apply too much caulk. A thick bead doesn't seal better. It just takes longer to cure and looks messy. Keep the bead no wider than the joint.
• Don’t apply sealant on a wet or dirty surface. The sealant needs to adhere properly, and it can't do that through moisture or old residue.
• Don't skip the foam backer rod on wide gaps. A sealant bridge across a large gap will crack.
• Don't apply sealant on cold days with temperatures below 5°C. Most products won't cure correctly in the cold. However, check the product label, as there are some low-temperature formulas made for Canadian winters. Either way, the best seasons for resealing windows are spring and fall, when temperatures are moderate.
• Don’t apply a new caulk bead without properly removing the old caulk bead.
• Don't apply caulk on rainy days.

Maintaining Your Seals Over Time

• Check your windows and doors every fall before winter. Look for cracks, gaps, or sealant that's pulling away from the surface.
• Clean the sealant with mild soap and water. Avoid abrasive cleaners that can scratch and weaken the surface. If you paint near your windows, use painter's tape to keep the paint off the sealant. Paint can cause it to peel.
• Proper window sealing done once and maintained regularly costs far less than dealing with water damage or replacing failed window frame components.

Why Do Properly Sealed Windows Reduce Energy Costs?

Properly sealed windows reduce the load on your heating and cooling systems because they reduce heat transfer and improve your home's overall energy efficiency.

Air leaks around windows are one of the main sources of heat loss in Canadian homes. When cold outside air comes in through window gaps, your heating system works harder to compensate. When the conditioned air escapes during the summer, you pay to replace it.

If the windows are properly sealed, that air exchange is significantly reduced. They won’t act like a solid wall, of course, but you’ll still notice the difference. In fact, it is estimated that drafts and air leakage through windows and doors can account for up to 25% of home heat loss.

If we’re talking about failed seals in double-glazed units, this means they’re not performing anymore. The inert gas between the panes is slowly escaping that space, so the energy performance of these units is diminishing day by day.

Need New Energy-Efficient Windows and Doors? Contact Magic!

Resealing extends the life of your windows, without a doubt. But if the window or door frame itself is the problem or if the double-pane window seal has failed, resealing is a short-term fix, whether it's a casement, sliding, or awning window. At some point (sooner than you think, most likely), you’ll have to replace your windows. If that’s something you might be interested in, you can book a free consultation with Magic to assess the condition of your windows and understand whether you need replacements.

Magic has been manufacturing windows and doors in Ontario since 1979. Our customers are happy with our technologically advanced systems: the Hybrid Fusion Frame, the Parallex Hardware, and the Slide’N’Hide technique, to name a few. Plus, we now also offer highly advanced front doors with superior weather sealing systems, so you can be comfortable in your house year-round. We serve the GTA and surrounding areas and install anytime, regardless of the season.

Ready to get the well-sealed windows you’ve been dreaming about? Give us a call!

FAQs

How to reseal double-pane windows?

If you notice condensation between panes in a double-pane window, the window seal has failed, and it cannot be replaced. Your best option is to replace the entire Insulated Glass Unit.

How much does it cost to reseal windows?

It costs around 80$ to reseal one window. The cost of hiring a professional to reseal windows can vary based on how many windows you want to reseal and the complexity of the job.

Can home windows be resealed?

Yes, you can reseal home windows by replacing worn caulking and weatherstripping. If we're talking about a failed window seal in a double-pane window, you'll likely have to replace the Insulated Glass Unit.

Do you reseal windows from the inside or outside?

You should reseal windows both on the inside and on the outside. Caulking needs to be applied both on the interior and on the exterior for superior weather protection.