Cracked or peeling caulk around a window lets in drafts, rain and insects, and it pushes up heating and cooling bills. The good news is that resealing a window is one of the easiest DIY home repairs. With a tube of caulk, a caulk gun and about 30 minutes per window, you can stop most leaks yourself. This guide shows you how to reseal windows step by step, which caulk to use, how to remove old caulk and the mistakes to avoid.
In this article
Signs Your Windows Need Resealing
- Caulk that is cracked, shrunken, peeling or missing in places
- A draft you can feel around the frame on a windy day
- Water stains, peeling paint or soft wood around the window
- Condensation or mold along the inside edge of the frame
- A candle or incense flame that flickers when you hold it near the frame
Most window caulk lasts somewhere between 5 and 10 years, depending on the product and how much sun and rain it gets. Check your windows every fall before cold weather arrives. Which side needs it most depends on which direction your house faces.
What You Need
- Exterior-grade caulk (see the table below)
- A caulk gun, ideally a smooth-rod or dripless model
- Utility knife and plastic or metal putty knife
- Rubbing alcohol and a clean rag
- Foam backer rod for gaps wider than about 1/4 inch
- Painter’s tape (optional, for neat lines)
- A caulk-smoothing tool or a damp finger in a disposable glove
Best Caulk for Windows
| Caulk type | Best for | Watch out for |
|---|---|---|
| 100% silicone | Exterior gaps between the window frame and siding or brick. Very flexible and water resistant. | Most silicone cannot be painted, and it sticks poorly to bare wood. |
| Polyurethane | Exterior joints that move a lot, and wood, metal or masonry. | Messier to work with and can break down in sunlight unless painted. |
| Hybrid (polymer or “advanced” sealant) | Exterior or interior jobs where you want flexibility and paintability. | Costs more than basic caulk. |
| Siliconized acrylic latex | Interior trim, where the window casing meets the wall. Easy to tool and paintable. | Not flexible enough for exterior gaps on leaky windows. |
As This Old House points out, silicone and polyurethane are the strongest choices for the outside of a window, while siliconized latex is best kept indoors. Always check that the label says it is suitable for windows and for the material you are sealing.
How to Reseal Windows Step by Step
1. Pick the right day
Work on a dry day when the temperature is at least 45°F (about 7°C) and no rain is expected for 24 hours. Caulk struggles to stick to cold or damp surfaces.
2. Remove the old caulk
Cut along both edges of the old bead with a utility knife, then pry it out with a putty knife. New caulk does not bond well to old caulk, so take out as much as you can. For stubborn silicone, a caulk-remover product helps soften it.
3. Clean and dry the joint
Brush or vacuum out dust and loose paint, then wipe the joint with rubbing alcohol. Let it dry completely. If you find soft or rotten wood, repair it first, because caulk will not fix structural damage.
4. Fill deep gaps with backer rod
If a gap is wider or deeper than about 1/4 inch, press foam backer rod into it first. This saves caulk and helps the bead flex properly.
5. Tape the edges (optional)
Run painter’s tape along both sides of the joint if you want a perfectly straight line.
6. Cut the nozzle and load the gun
Cut the nozzle at a 45-degree angle, with a small opening (about 1/8 inch) for narrow gaps. Puncture the inner seal, load the tube and squeeze until caulk reaches the tip.
7. Apply a steady bead
Hold the gun at a 45-degree angle and push or pull it along the joint at a steady speed, squeezing evenly. Work in one continuous line along each side of the window. Release the trigger at the end of each run so caulk does not keep oozing.
8. Smooth the bead
Run a smoothing tool or a gloved, damp finger along the bead to press it into the joint and leave a slight concave finish. Pull off the tape straight away, while the caulk is still wet.
9. Let it cure
Most caulk forms a skin within an hour or two and cures fully in about 24 hours, but some products take several days. Check the tube before painting or letting rain hit it.
Inside vs Outside: Where to Seal
| Location | What to do |
|---|---|
| Outside | Seal where the window frame meets the siding, brick or trim. This is the most important seal for keeping out rain. Leave the small weep holes at the bottom of vinyl or aluminum frames open, because they let water drain out. |
| Inside | Seal where the window casing (trim) meets the wall and the frame. This stops drafts and makes the trim look neat. |
| Moving parts | Never caulk the sashes shut. Use weatherstripping on the parts that open and close instead. |
Caulk vs Weatherstripping
Caulk is for gaps that do not move, such as the joint between the frame and the wall. Weatherstripping is for parts that move, such as the edges of a sash. According to the US Department of Energy’s Energy Saver guide, caulking and weatherstripping are among the simplest and most cost-effective ways to cut air leaks in a home. A thorough window reseal often uses both.
Common Mistakes to Avoid
- Caulking over old, cracked caulk instead of removing it
- Working on a wet or freezing day
- Using interior caulk outdoors
- Blocking weep holes at the bottom of the frame
- Laying a bead that is too thin to bridge the gap, or so thick it sags
- Painting silicone caulk (the paint will peel)
When to Call a Professional
Call a window installer or contractor if the frame is rotten, the glass seal has failed (fog between the panes), water is getting into the wall, or the window is on an upper floor you cannot reach safely from a sturdy ladder. A fogged double-pane window needs a new glass unit; caulk will not fix it.
Frequently Asked Questions
How often should windows be resealed?
Inspect them every year and expect to reseal every 5 to 10 years, or sooner on sunny, exposed sides of the house.
Can I caulk windows in winter?
It is best to wait for a dry day above 45°F. Some cold-weather sealants exist, so check the label if you need to make an emergency repair.
How much caulk do I need per window?
A standard 10-ounce tube usually covers one or two average windows on one side, depending on the gap size. Buy an extra tube so you are not caught short.
Should I caulk the top of a window?
Yes, seal the top and both sides on the outside. On many windows the bottom edge is also sealed, but leave any weep holes open so water can escape.
Final Thoughts
Resealing windows is a cheap, quick job that pays off in fewer drafts, less moisture and lower energy bills. Remove the old caulk, choose the right product for each side and lay a smooth, continuous bead. For more practical home repair and design guides, explore the latest articles on The Urban Splatter.
