How to Seal a Window and Door Step-by-Step

Indoors:

Step 1: Remove Trim

Remove interior trim around a window or door so you can access the space between the frame and the wall. First, cut through any dried paint along the edge of the trim with a utility knife. Then slide a flexible 3-inch putty knife behind the trim by a nail and pry out slightly. With the knife in place, wedge in a pry bar and pry the trim out an inch. If it seems as if the trim is about to crack, insert a second putty knife between the pry bar and the trim. Move to the next nail and repeat. Continue prying out the trim a little at a time down its length. Then go back to the beginning and pull the trim off.

BONUS TIP: You’ll need to use new nails when you reinstall the trim. To remove the old nails, don’t pull them back through the front of the trim. They might splinter the wood. Instead, pull them through the back using pliers. Use just enough pressure to pull the nails to avoid cutting them off. If one breaks off, use nippers to cut it as close as possible to the wood and leave it. That nub will just bury itself in the drywall when you reinstall the trim.

Step 2: Remove Insulation

Pull out any loose insulation that may be in the gap between the wall and the frame.

Step 3: Add New Insulation

Apply DAP No-Warp Foam in the gap. The insulating sealant fills both small and large gaps. Because the foam exerts very little pressure when curing, it won’t bow or warp windows. Make sure the surface is clean of debris. Shake the can. Then, holding it upside down, slowly pull the trigger to release the foam. The foam will expand to fill the gap, so fill it no more than 1/3 full.

BONUS TIP: Don’t try to wipe away any foam that gets on surrounding surfaces. Simply let it dry and then carefully scrape if off. If it gets on your skin, don’t try to wash it off (water accelerates curing). Wipe it off with a dry cloth.

Step 4: Remove Excess Sealant

After the foam has dried, use a utility knife to slice off any excess. Then reattach the trim.

Step 5: Seal Gaps

Clean out any debris in the gaps between the trim and the wall. Use DAP® ALEX FLEX® Premium Molding & Trim Sealant to fill and seal any gaps and cracks. It’s easy to apply and tool, low in odor, cleans up with water and is paintable in just 30 minutes. Cut the cartridge nozzle at a 45-degree angle to the desired bead size. Insert the cartridge into a caulk gun. Slowly squeeze the trigger to fill the gap with sealant. Tool the bead immediately, if needed, with a finishing tool.

If you’re outdoors, also do these steps:

Step 6: Inspect Gaps

Remove any old sealant between trim and siding. Clean out dirt and debris from the areas to be sealed so the sealant will adhere properly to the surfaces. Inspect the gaps: They should not exceed 2 inches wide by ½ inch deep. If the joint is deeper than ½ inch, insert foam backer rod into the gap before applying the sealant.

Step 7: Apply New Sealant

Fill gaps with DAP DYNAFLEX ULTRA Advanced Exterior Sealant. The product, commonly used to seal windows for all seasons, is rain- and paint-ready in just one hour. It not only improves productivity but also offers lifetime mold-, mildew- and algae-resistance, so the sealant stays looking clean and new. Cut the nozzle of the cartridge at a 45-degree angle at the desired bead size. Load the cartridge into a caulk gun and squeeze the trigger, using steady pressure as you move along.

Step 8: Clean Up and Paint

Clean up any excess sealant from surfaces with a damp cloth. No need for solvents or mineral spirits. Paint in just one hour with latex or oil-based paints.