Bonus Lesson Three

Cracked Glass – A Temporary Fix

Photography and Editorial By: Dr. Christopher Cooper

Many of us, during the restoration of our houses, have had to deal with cracked window glass from time to time. Cracked glass can cause all sorts of discomforts when a cold breeze is finding its way through the gap during inclement weather.

I hate to say it, but we as a society tend to only replace glass when it is completely broken-out; replacement of one cracked pane is usually low on our to-do-list. A testament to this is all the cracked glass in many of our project houses.

One of the biggest concerns for me is the large cylinder glass sheets in the 1877 replacement windows in the front facade of one of our project houses. They have large horizontal cracks from one side of the sash stile to the other; they have become very unstable and await final restoration before the glass is replaced. This type of crack could be potentially disastrous with our young daughters having the run of the place.

I have found that the best possible solution to stabilize cracked glass and to stop draft is to caulk both sides of the crack with a very high quality clear marine silicone caulk.

The Temporary Repair Process:

My apprentice, demonstrates placing masking tape on both sides of the window crack on the interior side of the window before using the silicone (see image 1). Approximately a sixteenth of an inch on either side of the crack is needed. For wavy or arched cracks, use a 2-inch-wide roll of masking tape and use a razor to trim away an eighth of an inch swath where the crack is; this will allow a smoother appearance. This step with the masking tape can be skipped if appearance is not a concern. Janet then simply runs a bead of silicone over the crack between the masking tape (see image 2).

Then, with a moistened finger, smooth out the silicone (see image 3). After the silicone is smoothed out, the masking tape is removed carefully so as not to ruin the uncured silicone (see image 4). Allow the interior repair to cure overnight and follow the same process as above on the exterior side of the glass.

The final temporary repair is relatively attractive and has stabilized the glass and stopped the draft. This is only a temporary fix and the cracked pane will eventually have to be replaced. However, it has made the pane safe for cleaning and for touching with little hands that have the run of the place!