The short answer
Find the Leak Source
Start by checking the window from inside and outside on a dry day. Look for gaps, cracks, or missing sealant around the glass, the frame joints, and the sill. Run your hand along the edges to feel for drafts or damp spots. Water often enters at the bottom corners or where the frame meets the wall.
If you see water stains on the wall or floor, the leak may have been active for a while. Probe the area with a screwdriver to check for soft, rotted wood. If the framing feels spongy, the damage goes beyond the seal, and you may need to replace the window or call in a pro for water damage inspection.
Gather Your Tools
You need a putty knife or scraper, a wire brush, a rag, and a solvent for cleaning. Also get exterior-grade caulk or sealant, a caulking gun, and a smoothing tool or your finger. Choose a sealant labeled for windows and outdoor use, such as a silicone or polyurethane product. Avoid low-cost acrylic that cracks in weather.
Wear gloves and eye protection. If the old sealant contains lead or asbestos, which is rare in modern windows, stop and consult a professional. For most homes, the job is straightforward, but you must work in dry conditions. Check the weather forecast and pick a day with no rain for at least 24 hours.
Remove Old Sealant
Use the putty knife to scrape away all old caulk and sealant from the joint. Be careful not to damage the glass or the frame. A wire brush helps remove stubborn bits and loose paint. Vacuum or wipe away dust and debris. The surface must be clean and dry for the new sealant to stick.
If you find mold or mildew, clean it with a bleach solution and let it dry completely. Do not seal over moisture or rot. For large gaps wider than a quarter inch, you may need backer rod or foam backing before you apply the sealant. That gives the sealant something to grip and prevents sagging.
- Scrape off old caulk with a putty knife
- Brush away loose paint and dirt
- Clean with solvent and let dry
- Check for gaps wider than 1/4 inch
- Use backer rod for large openings
- Dry the area completely before sealing
Apply New Sealant
Load the sealant tube into the caulking gun and cut the nozzle at a 45-degree angle. Apply a steady bead along the joint, pushing the gun smoothly from one end to the other. Keep the tip in the sealant as you go to avoid air pockets. Work in short sections if the window is large.
After applying, smooth the bead with a wet finger or a smoothing tool. This presses the sealant into the joint and creates a watertight barrier. Wipe away excess with a damp rag. Let the sealant cure fully according to the label, usually 24 to 48 hours, before you expose it to water.
Test and Monitor
After the sealant cures, test the window with a hose from outside. Spray water at the window from different angles for a few minutes. Check inside for any new leaks. If you see moisture, the leak may come from elsewhere, such as the roof, the wall, or the window flashing.
In Redmond, you might want to check your window seals before the wet season starts. If leaks keep returning, the window frame or the surrounding structure may be damaged. At that point, consider window replacement or a professional water damage inspection to assess hidden rot and moisture buildup.
- Hose test the window after curing
- Check for leaks at corners and sill
- Inspect flashing and roof for other sources
- Watch for recurring moisture after rain
- Call a pro if you suspect structural damage
Need help right now?
Phones are answered 24/7 for Redmond and nearby communities.
Call Now (425) 407-5186Frequently asked questions
Can I use any caulk for a window seal?
No, use exterior-grade sealant designed for windows. Silicone and polyurethane work well because they resist UV and temperature changes. Avoid acrylic caulk that cracks in weather. Check the label for outdoor use and compatibility with your window material.
How long does window sealant take to dry?
Most exterior sealants cure in 24 to 48 hours, but it depends on temperature and humidity. Read the label for exact times. Do not let rain touch the sealant before it cures. For wet climates, pick a dry stretch to do the job.
What if the leak comes back after I seal it?
If the leak returns, the problem may be beyond the seal, like cracked flashing or rotted framing. You might need a window replacement or a professional inspection. Water damage can spread behind walls, so catch it early. Check your policy to see what is covered. Policies vary, and your insurer decides what is covered.