How to Repair a Lost Seal on a Thermopane Window

Keeping your windows sealed is a great way to maintain the insulation of your home, keeping it warm in the winter and cool in the summer.

Double pane windows work by creating a tiny airspace between two panes of glass which reduces the amount of heat escaping or entering your home.
Sealing your windows will help you cut down on your electricity use and lower your heating bill. Many windows will lose their seal over time. Rather than replacing the entire window you can replace the seal at home using silicone caulk. This will ensure that your double-paned windows continue to work properly. .

Put on your work gloves and your safety glasses. Strip the larger portions of the old or damaged seal on your double paned window using the utility knife. Discard the old seal. Apply a light coating of caulk solvent if pieces of the old seal remain. Wait an hour, then remove the remaining pieces of the seal with the putty or utility knife after the solvent has softened them.

Wipe the area down with a damp rag with soap and water (do not use harsh cleansers). Allow the area to dry.

Cut the tip of the tube of silicone caulk at an angle using the utility knife. Guide the wire down the hole you created and puncture the foil seal inside the caulking tube. Make sure that the pressure lever on the caulking gun is fully extended. Insert the caulk tube into the caulking gun and gently apply the pressure lever to the bottom of the silicone caulk tube. Do not squeeze the handle until you are ready to apply caulk.

Put the tip of the silicone caulk tube in the left corner of the window that you wish to seal, or at the top of the area if you wish to seal a vertical portion of the window. Squeeze down on the trigger. Once the caulk begins to flow from the end of the caulk tube, slowly draw the tip of the tube across the gap to be sealed. Keep even pressure on the trigger and apply the caulk uniformly from left to right.

Allow the caulk to set for at least 24 hours. After 24 hours check that the area is adequately sealed with no obvious gaps. Seal any other areas of the window using the above steps.

Things You Will Need

  • Safety glasses
  • Work gloves
  • Utility knife
  • Putty knife
  • Caulk solvent (optional)
  • Wire
  • Silicone caulk
  • Caulking gun


  • Remove the caulk tube from your caulk gun once all of your caulking projects have been completed. Often the caulk will harden through minor gaps in the caulking tube and may get stuck in your caulking gun, rendering the caulking gun unusable for future projects.


  • Avoid touching the silicone caulking until it is completely dried.
  • Avoid dripping the silicone caulking on your clothes.
  • Always puncture the seal before inserting the caulk tube into the caulking gun. If you do not puncture the seal then you run the risk of driving the pressure lever into the caulking tube and rendering it unusable.

About the Author

Based out of Wrangell, Alaska, Ryan Long has been a professional writer and photographer since 2007. His work has appeared in the "Wrangell Sentinel," "Homer News," "Frommer's Travel Guide," "Juneau Empire," "Ketchikan Daily News" and "The Seattle Times." Long has a Bachelor of Arts in English literature from Michigan State University.

Photo Credits

  • Jupiterimages/BananaStock/Getty Images