One of the most common repairs you need to know is how to replace glass on steel windows. So, I’ll walk you through how to get it done safely and quickly.
Replacing glass in steel windows often results in the glass breaking on its way out if it isn’t already broken. Steel windows often have cement putty used in them, which is exactly like it sounds. Incredibly hard and stubborn, and feels like it takes a pack of dynamite to get it out sometimes.
If you want the whole process I use to restore historic steel windows in detail, get a copy of my Craftsman’s Guide to Restoring Steel Windows.
Steel windows have a couple hazards that you should mindful of before starting. Lead paint is often present on steel windows and glazing putty made in the first half of the 20th century may contain asbestos. Read these posts before getting started to make sure you are being safe.
How To Replace Glass on Steel Windows
Now that we’ve covered the safety tips, we can get into the nitty gritty of replacing that pane of glass.
Step 1 Remove Old Putty
Using a 1/2″ chisel and a hammer, dig out the putty on the exterior of the pane that needs replacement. Make sure you remove as much as possible to give the glass room to come out.
Step 2 Remove Spring Clips
Depending on the manufacturer of your windows, you will have between 2 and 4 spring clips per pane of glass. Remove these clips by prying them out of the frame with the chisel.
Step 3 Score the Paint
Move to the inside of the window and score the paint/putty line on the glass to break the seal.
Step 4 Knock Out the Glass
Wear gloves and glasses to protect yourself against getting cut by the glass in this step. I prefer to do this with a partner on the outside to hold up a piece of plywood to cover the opening because glass can shatter here.
Using a rubber mallet or a regular hammer with a rag wrapped around the head, bang around the edges of the glass from the inside to break it free of the frame.
More than half the time I end of breaking the glass and pulling it out in pieces very carefully, but since you were planning to replace the glass anyway…
Step 5 Clean Up
With all the glass out, finish removing any remaining putty from the frame using your chisel.
Step 6 Bed New Glass
Back bed the frame with your choice of glazing putty. I prefer Sarco DualGlaze, but any putty that is designed for steel windows will work just fine. Cut replacement double-strength glass to fit your opening and be sure to leave the replacement glass at least 1/16″ smaller than the opening to avoid it cracking from expansion in the future. From the outside, firmly set the new glass into place by pressing it into the glazing bed until most of the putty has squeezed out on the inside. Set new spring clips in the locations where the old ones were to hold the glass firmly in place.
Step 7 Finish Glaze
Apply glazing putty to the outside and tool it to a smooth beveled surface with clean mitered corners. For more tips on how to finish glaze watch my video How to Reglaze Your Old Windows. Once you’re happy with the glazing, clean the glass of any remaining oils with some whiting being careful to avoid disturbing the finish glazing.
That’s it! Start to finish the whole process shouldn’t take you more than 1 hour even if you’ve never done it before.
Historic steel windows can be really beautiful when restored and surprisingly efficient once tuned up properly. If you’re contemplating restoring I would definitely recommend you read my guide on the process. I’ve included all the information you need in one easy to follow eBook.