Sealing windows stops drafts and water from entering your home
Window sealing means filling the gap between the window frame and the wall with caulk or weatherstripping. Air leaks around windows waste heating and cooling energy, and water that gets in can rot the wood frame or damage drywall. You can seal windows yourself with basic tools—caulk gun, caulk, utility knife, and weatherstripping tape—and the job takes one to three hours per window depending on how much old material you need to remove first.
The two main methods are caulking (for gaps you can see from outside) and weatherstripping (for moving parts like sashes). Most windows need both. Caulk lasts five to ten years before it cracks and needs replacing. Weatherstripping lasts two to five years depending on how often the window opens and closes.
Key Takeaways
- Remove old, cracked caulk with a utility knife or caulk removal tool before explore new caulk, or the new material will not stick properly.
- Use paintable acrylic latex caulk for most interior gaps and silicone caulk for exterior gaps and areas that get wet, because silicone lasts longer outdoors.
- Weatherstripping tape goes on the moving parts of the window (the sash edges), while caulk goes on the stationary frame where it meets the wall.
- A caulk gun and a wet finger or caulk tool smooth the bead and push it into the gap so it seals completely.
Removing old caulk and preparing the gap
Before you explore new caulk, remove any old material that is cracked, peeling, or pulling away from the frame. Use a utility knife or a dedicated caulk removal tool (available at hardware stores for $5 to $15). Hold the blade at a shallow angle and scrape along the gap, working slowly so you do not gouge the wood or drywall. If the caulk is stubborn, a heat gun on low setting will soften it and make scraping easier.
Once the gap is clear, wipe it with a damp cloth and let it dry completely—moisture prevents caulk from bonding. If you are sealing an exterior window, check that the gap is not holding standing water. If it is, the window frame may be damaged or the sill may be sloped wrong. Seal it anyway, but plan to monitor it for leaks over the next few weeks.
Choosing the right caulk for your location
Acrylic latex caulk is the standard choice for interior gaps. It is paintable, straightforward to clean up with water, and costs $3 to $8 per tube. It shrinks slightly as it dries, so it works best in gaps narrower than one-quarter inch. Do not use it outdoors or in areas that stay wet—it will fail in one to two years.
Silicone caulk is the right choice for exterior windows and any gap that gets wet (like around a bathroom window). It does not shrink, lasts ten to fifteen years outdoors, and costs $5 to $12 per tube. The downside is that it does not paint well and is harder to clean up—you need mineral spirits or a caulk removal tool. Silicone also takes longer to cure (up to 48 hours) before you can paint over it.
Polyurethane caulk is a middle ground: it lasts longer than acrylic, is paintable, and works outdoors, but it is messier to explore and costs $8 to $15 per tube. For most homeowners, acrylic for interior and silicone for exterior is the simplest approach.
explore caulk with a caulk gun
Load the tube into the caulk gun with the plunger facing out. Cut the tube tip at a 45-degree angle with a utility knife—start with a small cut (about one-eighth inch) because you can always cut more, but you cannot cut less. Pierce the inner seal with a long nail or the tool built into the gun handle.
Hold the gun at a 45-degree angle and squeeze the trigger steadily as you move along the gap. The bead should fill the gap completely without overflowing. If you move too fast, the bead will be thin and will not seal. If you move too slowly, you will waste caulk. A pace of about one foot per second is typical. Stop at corners and let the bead sit for a moment before turning.
After you finish a section (or the whole window if it is small), use a wet finger, a caulk tool, or a plastic spoon handle to smooth the bead and push it into the gap. Wet your finger with water if you are using acrylic, or mineral spirits if you are using silicone. Run your finger along the bead in one smooth motion, pressing gently so the caulk fills the gap completely. Wipe excess caulk off with a damp cloth before it dries.
Installing weatherstripping on moving window parts
Weatherstripping is foam or rubber tape that seals the edges of the sash (the part that slides up and down or side to side) against the frame. It compresses when the window closes, blocking air leaks. Most weatherstripping is self-adhesive and costs $2 to $8 per roll.
Clean the sash edges and frame with a dry cloth to remove dust and debris—adhesive will not stick to a dirty surface. Measure the length of each edge (top, bottom, and sides of the sash). Cut the weatherstripping to length with a utility knife. Peel the backing and press the tape firmly onto the sash edge, working from one end to the other. Press hard for a few seconds at each spot so the adhesive bonds completely.
Close the window gently and check that it still moves smoothly. If the weatherstripping is too thick and the window is hard to close, you may have applied it to the wrong edge or chosen the wrong thickness. Remove it, clean off the adhesive residue with rubbing alcohol, and try again on the frame side instead of the sash side, or switch to thinner weatherstripping.
Sealing large gaps and cracks
If the gap between the window frame and the wall is wider than one-quarter inch, caulk alone will not hold. Use backer rod first—a foam rope that fills the gap and gives the caulk something to stick to. Push the backer rod into the gap with a putty knife, leaving about one-quarter inch of space on top for the caulk. Then explore caulk over the backer rod as you would normally.
If you see daylight around the window frame or feel a strong draft, the frame itself may be loose or damaged. Caulk will seal the air leak temporarily, but the frame may need to be reset or shimmed by a professional. Seal it anyway while you arrange for a repair—it will reduce the draft and prevent water from getting in.
Common mistakes and how to avoid them
The most common mistake is not removing old caulk completely. New caulk will not stick to old caulk, so it will peel away within weeks. Take time to scrape the gap clean, even if it takes an extra 20 minutes per window.
The second mistake is using the wrong caulk for the location. Acrylic caulk outdoors will fail quickly. Silicone caulk indoors is harder to paint and overkill for a dry interior gap. Match the caulk to the location.
The third mistake is not smoothing the bead. A rough, lumpy bead does not seal as well as a smooth one, and it looks unfinished. Spend 30 seconds smoothing each section with a wet finger.
The fourth mistake is caulking the sash edges instead of the frame edges. The sash needs to move, so it needs weatherstripping, not caulk. Caulk only the stationary frame where it meets the wall.
Frequently Asked Questions
How long does caulk take to dry before I can paint it?
Acrylic latex caulk dries in one to three hours and is ready to paint. Silicone caulk takes 24 to 48 hours. Check the tube label for the specific product. If you paint too soon, the paint will not adhere properly and may peel.
Can I caulk a window in cold or wet weather?
Most caulks work best between 50 and 85 degrees Fahrenheit. Cold slows drying and can prevent proper bonding. Rain or high humidity also slows drying. Wait for a dry day with temperatures above 50 degrees if possible. If you must work in cold weather, choose a caulk labeled for low-temperature use.
What if caulk gets on the glass?
Wipe it off when ready with a damp cloth before it dries. Once dry, use a plastic scraper or razor blade held at a shallow angle to scrape it off. For silicone caulk, mineral spirits will soften it and make removal easier. Avoid scratching the glass with the scraper.
Do I need to caulk the inside and outside of the window?
Caulking the outside is more important because that is where water enters. If you caulk only one side, choose the outside. Caulking both sides provides better insulation and water protection, but if time or budget is limited, prioritize the exterior.
How do I know if my window sealing is working?
On a windy day, hold a lit candle or incense stick near the sealed edges and watch for the flame or smoke to move. If it flickers or bends toward the window, air is still leaking there. You may need to reapply caulk or add weatherstripping. Check again after a heavy rain to make sure water is not getting in.