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Old-House Online » Old-House Tips, Restoration Stories, & More » Repairs & How To » How To Repair a Steel Window

How To Repair a Steel Window

Replacing broken glass in a steel casement window requires specialized tools and processes. By Steve Jordan | Photos by Andy Olenick

    Repaired steel casement windowReplacing a broken pane of glass on a steel casement window isn’t like repairing wood sash. It takes different tools, special materials, and a fine-tuned process. But once the former are assembled, the job is easy enough for anyone with a little DIY experience and a willing attitude.

    Step 1

    Assemble your materials, starting with the glass. Unless your glass is ordinary 1⁄8″ double-strength sheet glass, purchase 3⁄16″ or 1⁄4″ plate glass at a glass supplier to match the existing. (The new pane of glass should be about 1⁄8″ narrower than the opening’s height and width.) Steel sash should be glazed with putty specifically made for metal windows, such as DAP 1012. (Wood window putty won’t last.) You’ll also need an awl and hammer, metal sash clips, duct tape, a wire brush, needle-nose pliers, a small window suction cup, and whiting.

    Materials for repairing a steel window

    Step 2

    Wearing eye protection and a respirator and using basic lead-safe work practices, begin removing the old putty. Because old putty can be hard and may contain lead, Portland cement, or asbestos powder, use an awl and hammer, not heat, to loosen it. Look for areas where the putty is loose or missing, insert the awl point between the putty and steel, and gently tap the awl with your hammer; the force needed will depend on the condition of the putty and its composition. If the putty is intact, start from the middle.

    Removing old putty

    Step 3

    Once the putty is removed and the edges of the glass are exposed, look for two metal spring clips on each vertical side of the opening; pull them out with the needle-nose pliers. These clips are fragile and easy to lose; if you can hold onto them and they remain intact, you can reuse them. Otherwise, purchase new ones at a glass company. Next, with the ground and floor protected to catch glass shards, old putty, and dust, cover both sides of the glass with wide masking or duct tape to contain breakage. If the pane isn’t badly cracked, pull it out using a small window suction cup, or by tapping gently from the inside out. With the glass out, finish removing the old putty. If the sash rebate is rusty, use a wire brush or a drill and wire brush attachment to remove as much rust as possible. Brush or vacuum the dust away, and prime the cleaned area with a coat of oil-based rusty-metal primer.

    Cleaning up rust

    Step 4

    Since DAP 1012 is usually oily on top of the can and dense at the bottom, remove all of the material and knead it into a pliable ball, using whiting if necessary to firm it to an appropriate consistency. (If the putty is dry on the top of the can, return it for fresh material.) The new pane of glass can’t touch the metal frame in any direction, so back-bed a thin layer of putty in the frame to seat the glass, protect it from thermal movement, and create a weather seal. Install the back-bed with your fingers or a putty knife, pushing the putty into the frame (warm putty is more pliable). Next, insert the pane of glass, and gently push it into the putty until it is well-seated. Using needle-nose pliers, install the metal sash clips on each side to secure the pane.

    Inserting sash clips

    Step 5

    Before glazing, remove excess back-bedding material from the interior side with your putty knife. Next, glaze the exterior—I like to push the putty into the frame and glass tightly with the putty knife, but the common method of rolling putty into a snake and then inserting it also works. Take care to respect the interior sight lines of the sash—putty and paint on the outside shouldn’t be visible from the inside. Tool the putty, pushing it tightly to the frame and glass while cutting the edge away at the sight line. To finish, sprinkle a little whiting or plaster dust on a clean cotton rag, and carefully wipe away all the smears. After the putty dries, paint with two coats of oil-based paint.

    Applying putty
    Published in: Old-House Journal February/March 2013


    Catherine Brooks, Eco-Strip June 20, 2013 at 10:47 am

    Why wouldn’t low infrared heat (Speedheater), which does not vaporize lead, be used? With glazing on wood windows, it safely softens the glazing and therefore, reduces the risk of breaking the glass with an awl, sharp chisel, and a hammer. Scraping SOFT, heated, old lead-based paint and putty generate less lead dust and further reduce the risk of lead poisoning than does dry scraping.

    Linda Forrest September 21, 2014 at 3:26 pm

    I have a house with metal windows and can’t find anyone who can repair. Where should I go? Can you help me out?

    Jay October 17, 2014 at 11:16 am

    Linda Forrest, where are you located? I’ve been puttying windows for many years and I’m actually in the middle of doing a bunch of metal windows on my own house with metal clips. I’m in Cleveland, Ohio.

    Marcia Schmit October 30, 2014 at 9:01 pm

    I could really use some helpful advice. I have a 1945 concrete block cottage ranch in Arizona. The main house has 17 BIG steel-frame casement windows; ALL of which need to be redone.. I’m probably going to have to do in situ, myself . Can’t take them out. And all the work that needs to be done on each window…it is not a one-step, or 1-2 day process. Want to do it over the winter when I don’t run the AC.

    Greg F December 1, 2014 at 5:55 pm

    RE:Sash clips

    Exactly what are sash clips and how do they install? I am planning on replacing single glazed panes with insulated 3/8″ units, but can find nothing on these…

    Lauren St. J April 16, 2015 at 9:27 am

    We bought a 1938 stone and brick house in Alexandria, VA in November. I’d like to refurbish 19 steel casement windows. All but 1 has been painted shut and I’d like to be able to open them especially in case of fire.

    I could probably do the inside myself but I’m sure there has been lead paint applied at some point. And the upstairs bedroom windows are 3 levels above ground in the rear. So I think I’d rather hire someone to do the project.

    Can you recommend anyone in Northern Virginia who does work like this?

    Elena H April 30, 2015 at 1:36 pm

    I’ve just gotten started on trying to restore the metal windows on my garage–the paint is peeling, the putty is falling off, and apparently the previous owner’s lawnmower had a habit of spitting gravel at the windows, because there are tons of holes in the glass. (I’m planning to replace the glass with acrylic in case future lawnmowers have the same habit.)

    I’m at the stage of trying to remove the old, hardened glazing putty. Some of it is in bad enough shape that I can just break it off with my fingers, but some looks to be in great shape… albeit with horrible peeling paint flaking off on top of it.

    Since some of the old glazing putty is in good shape–I only plan to replace the broken panes–and since the stuff in good shape is REALLY hard to remove, is patching rather than replacing a viable option? In other words, will putting new putty beside or even on top of old putty work, or is it important for me to remove every scrap of old?

    Also, will the citrus-based (Citristrip) stripping gel I bought for the job harm the old glazing compound? For the most part, the paint over the old glazing putty is easy to remove by hand, but when I strip the metal sashes I expect that a bit will make its way onto the putty area whether I want it to or not.

    Antoinette Todino August 2, 2015 at 3:52 pm

    I would like to refurbish 9 steel casement windows and mend steel screens for a 1932 Tudor. Five years ago the windows were painted which caused them not to open easily. My concern is lead and asbestos leeching if not handled properly.

    I live in Mt.Vernon, NY. Could you recommend someone who has expertise in this area and uses green products?

    Thank you for your time and interest.

    Angie Wilson November 9, 2015 at 4:01 am

    Hi, I have bought a grinder to remove very hard putty, as tried chipping out the old stuff and it is concrete gard, it would take an age to remove 8 panes. I do not want to pay an excessive amount on a new window frame. Will the grinder work? Thanks.

    Tom OQuinn February 26, 2016 at 6:46 pm

    Great company called Seekircher Steel Window Repair you should contact…. They are the best

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