How to Replace a Broken Window Glass Pane

January 24, 2021 Updated: January 24, 2021

Dear James: We have older wood windows, and some of the glass panes have cracks but are intact. What is the easiest and best method to replace the glass panes myself? —Denise K.

Dear Denise: Replacing a glass pane in a wood window sash is not rocket science, but it is often done wrong. The glass pane may stay in place, but a do-it-yourself job is easy to notice. The putty lines are often not straight or even, and the paint usually gets over the glass pane.

There are other potential long-term problems from a poor glass pane replacement project. If the wood surface, which the putty contacts, is not prepared properly initially, the putty can dry out and crack. The cracks allow moisture to get into the wood, which can damage the sash over time.

The first step before removing the old broken glass from the window sash is to wear the proper protective clothing. This includes heavy work gloves; a thick, long-sleeved shirt; and large eyeglasses (preferably goggles). Don’t forget to wear heavy leather shoes in case you drop a piece.

Take your time, and do not try to remove several pieces of the broken glass at one time. Grab hold of each large piece, and wiggle it slightly to make sure it will not knock others loose when you lift it. When you are sure it is not supporting other pieces, wiggle it loose from the old putty, and remove it.

For a glass pane with just one crack across it, consider just gunning a bead of clear silicone caulk over the entire crack on each side. This seals the glass and really does not look bad.

If you do want to remove a glass pane with just one long crack through it, don’t break the glass into smaller pieces, which will be easier to remove. It is safer to remove all the putty first and remove each piece of glass intact. Using a heat gun can make old, hardened putty more flexible and easier to remove.

Once all the broken glass is removed from the sash, remove all the remaining old putty. Make sure to get all the way down into the corners, and don’t miss any of the small glazier’s points. Check for high spots, and smooth them out with a wood chisel.

Now you are ready to install the new glass pane. Using a small paintbrush, coat the cleaned wood sash surface with pure linseed oil. The linseed oil is good for the wood, and it keeps the putty from drying out and cracking from the inside. This can add many years of life to the putty.

Butter the inside of the sash frame, where the pane will rest, with a 1/16-inch layer of putty. This step is often skipped by do-it-yourselfers. Gently press the new pane of glass into this layer of putty, making sure there are no air pockets. Place glazier points every 4 inches around the pane to center and hold it in place.

Roll the putty in your hands to form a long bead. Start at one corner, and continue all around the perimeter of the pane. Smooth it out with a putty knife. The instructions on the putty can will indicate the wait time until it can be painted.

Epoch Times Photo

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