Dual-pane windows: replace or repair?

Homeowner seeks cheap fix for leaky cells

Bill and Kevin Burnett
Inman News

Q: I’ve read your recent column about windows and have some related questions.

I have dual-pane windows whose cells have “leaked” and the inside surfaces are discolored. They are installed in traditional wood frames and are easy to remove. They have a metal/plastic composite spacer frame at the edge, sealed with some sort of black mastic. I have a number of cells that were replaced under warranty when water leaked inside and would like to see if I can rehab them.

If I can remove the spacer from one side, I could then clean the inside surfaces. Would isopropyl alcohol be a good cleaner, or would you advise something else?

Then, how would I ensure that I remove all possible water vapor before I reseal the edge? By moderately heating the cell? Or by injecting some type of gas? I would reseal with some type of mastic. Then I would put a layer of sealant all around the perimeter to try to plug the original leak.

Buying new replacement cells costs a bundle, and I have nothing to lose by trying to rehab these.

A: Our first reaction is to bite the bullet and buy new replacement Insulate Glass Units (IGU). They are expensive, but repairs can fail. Last winter, Kevin’s daughter, Katie, busted the inside of a double-glazed window in their family room. Kevin thought about doing the repair, but it was in the middle of an Idaho winter and wife Heidi wouldn’t stand for the delay.

The 3-by-3-foot IGU cost Kevin $130 and he did the installation himself. Unlike Kevin, you’ve got the time to tackle this job. You’ve also got the inclination. We say go for it.

You’ve got nothing to lose save perhaps a piece of glass you might break during the repair attempt. We wouldn’t try to remove the spacer from one side and clean the two pieces of glass through the 1/2-inch slot. That’s an impossible task, in our view. Rather we suggest that you remove one pane of glass entirely from the IGU, cleaning both interiors and resealing the IGU sandwich.

Begin by removing one of the window panes from the frame and laying it on a flat surface. A table covered with a towel should work just fine. On the edge of the window you’ll see a black, rubber-like material. This is a butyl sealant. Part of the reason the window failed is the sealant failed.

To separate the glass from the butyl use a utility knife with a new blade to break through the butyl where it meets the glass. Remove the knife blade and insert a new hacksaw blade between the glass and the spacer. Saw back and forth as you work your way around the edge of the glass. When you’ve sawed around the perimeter of the pane, remove the single pane of glass, leaving the other pane with the spacer on the table.

After the first pane is separated, it’s time to clean the insides of both panes and the spacer. Lay rags on top of the good piece of glass to catch any debris, and, with a putty knife, scrape the surface of the spacer that will come in contact with the new glass. Remove the rags and debris and vacuum the window to remove any little bits of gunk. Clean the inside of the piece of glass that you didn’t remove.

Remember, once you install the new glass, any debris or finger marks on the inside will be permanently sealed. So, clean it meticulously and check it from all angles for smudges. Use a solution of 1 cup isopropyl alcohol, 1 cup water and 1 tablespoon white vinegar to clean the glass. Use a hair dryer set on low temperature to be doubly sure you’ve gotten rid of excess moisture.

Now you’re ready to replace the other pane. Clean the side of the glass that will sandwich onto the inside of the pane and dry it with the hair dryer. To make the sandwich, run a thin bead of clear silicone around the perimeter of the spacer. Set the glass on the spacer and use finger pressure to adhere the glass to the silicone all the way around. This will ensure the glass is embedded into the silicone, making an airtight seal. Finally, run a generous bead of silicone around the side of the pane, making sure to cover where the glass and spacer meet. Cover the pane with a towel for 24 hours to allow the silicone to cure. After 24 hours, you can install the pane back into the opening.

There are a couple of things that can go wrong. The first one is the possibility of leaving marks on the inside portion of the glass. Once the glass is sealed, cleaning is impossible. Meticulous cleaning will prevent this.

The more troubling one is that the seal can fail, resulting in condensation between the panes. There’s a good chance that with the slightest break in the silicone seal you will begin to see moisture form as soon as the nights get cold and the days get warm. All your work will be for naught, but you won’t be out any money.



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