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How To: Replace Broken Window Glass

Broken-window-glassWhether it’s an errant baseball or a tropical storm, windows are bound to break sometimes. And before you call a window specialist to replace your broken window glass, you might just be able to do it yourself. More importantly, if you have an old house, your broken window glass will need to be replaced in a different way than most specialists know how to do today.


What’s Different About Historic Windows?

Old wood windows (typically pre-1950s) were almost always putty glazed (you can watch our video on how to putty glaze windows here). Most window contractors today don’t know how to putty glaze, and when confronted with a historic window, they use caulk or some other product not intended for these old windows. This can create a host of problems for your old windows. It’s always best to replace materials on a historic home with in-kind materials so that the repair blends seamlessly and doesn’t stick out like a band-aid. Here’s how to do it!

  1. Remove the Broken Glass – Wearing gloves and glasses, carefully remove the remaining pieces of broken window glass and dispose of them safely.
  2. Clean the Rabbet – Clean the old glazing putty from the rabbets on the outside of the window. Use a firm putty knife for this and be careful not to gouge the soft window wood while you scrape the putty out.
  3. Remove Any Glazing Points – There may be some glazing points (little metal triangles or diamonds) remaining in the rabbets. Using needle nose pliers, pull them out and dispose of them too.
  4. Wipe On Boiled Linseed Oil – Once the rabbets are clean of old putty and glazing points, wipe them down thoroughly with Boiled Linseed Oil (it’s available in the paint section of any hardware store).
  5. Cut Your Replacement Glass – Measure the width of the opening for your replacement glass. You can either cut your own window glass, or take the measurements to your local hardware store and have them cut it for you. Important: Be exact on these measurements! You have to cut the glass 1/16″ smaller than the opening otherwise the glass may break as the wood swells in certain weather. Glazing rabbets are very small so your measurements have to be precise. This is the hardest part. Just remember the old saying “Measure twice, cut once.”
  6. Glaze the Rabbet – Add glazing putty to the rabbet. This will create an air tight cushion for the glass to rest in. For repairs outside the shop, I recommend Sarco Dual Glaze putty. It can handle the elements better than other putties and excels in this application. But there are other acceptable types of glazing putty.
  7. Bed Your Glass – Put your replacement window glass into place and press it gently but with firm pressure around the edges into the glazed rabbet. This will cause some putty to squeeze out over the inside of the glass which we’ll clean later.
  8. Set the Glazing Points – Glazing points are what hold the window pane securely in place. Depending on the size of your replacement window glass, you may need more or less points. A good rule of thumb is to use one point for every 12″ of width and at least one point on each of the four sides. Bottom line, too many is better than too few.
  9. Glaze the Window – Spread a fair amount of putty around the edges of the window and really push it into place. It doesn’t have to be pretty at this point.
  10. Tool the Putty – Run your putty knife along the length of the window to smooth the putty at a bevel. Come back and make nice clean corners. You can mess with the putty as much as you want. If it doesn’t look good, keep tooling it until you are happy with the results. For a more in depth explanation of glazing watch our video: How To Reglaze Old Windows.
  11. Clean the Glass – Brush on some whiting to clean the window glass of oily fingerprints from the putty (this video will show you how) and you’re done!

You’ll have to let the putty sit a few weeks until it “skins over” and is ready for paint. Don’t wait too long to paint. Glazing putty won’t survive long without paint. It can mildew and fail in a few short months when not painted. But when painted it should last decades without much maintenance.

For more on working with old windows you can visit our resource page How To Repair Old Windows.

Step-by-Step in Pictures



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20 thoughts on “How To: Replace Broken Window Glass

  1. Thanks for the tip that proper glazing is important to do when it comes to commercial window replacement. My aunt recently found a good commercial space where she can start her own business but some of the windows are cracked due to the age of the building. It would be best to focus on renovating the place first in order to make it look good as new.

  2. Scary handling glass but this article gives me hope. Very helpful and we plan to tackle one window this week. We have several that are cracked and need replaced.

    1. Hi Carol,
      Thanks for sharing your project and process! We’re always so glad to hear that our articles help real people with real projects. That’s why we do what we do!
      -Alyssa at The Craftsman Blog

  3. My son accidentally broke a window in my living room the other day, so I’ve been trying to fix it the last few hours. I like that you suggest adding a glazing putty to the rabbet to create an airtight cushion for the glass. This sounds like a great way to keep air sealed inside and give it some padding if it vibrates. Thanks for sharing! http://www.areaglass.com/services

  4. Our window needs replacement after it was broken by a large metal pipe during the storm. By the looks of it, I think it’s laminated glass. I like how you mentioned wearing gloves and removing the broken window parts with care since that’s a safety precaution. But I need to have someone help me do it because I’m worried. Thanks for the article. I learned a lot.

  5. One of my kids accidentally broke one of our living room windows the other day, so I’ve been looking for ways to go about replacing it. I like that you suggest adding glazing putty to the rabbet. This sounds like a good way to give it more pressure and prevent drafts in the winter. Thanks for sharing! http://www.archdesignwd.com

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  8. Love the advice here! We get tons of calls every week from someone looking for replacement glass, NOT replacement windows. We always recommend one of two businesses local to us that do good work, but it’s nice to keep up with the industry. Thanks!

  9. Where do you suggest we get replacement glass? The kind of glass sold at the chain hardware stores isn’t wavy like our original glass from 1922.

    1. I need to replace a couple of broken basement windows which are single strength according to your window book I purchased. The rabbets are 1/2 inch deep and I’m wondering if I am able to use 1/4 inch safety glass or if I’m limited to 1/8 inch. If so I’m curious why.

      1. Ian, you can use 1/4″ safety glass but there are a couple things to do. First, seal the edges of laminated glass with a latex paint first before putty glazing otherwise the oil will ruin the seal. Second, make sure the finish glazing isn’t too small otherwise that can shorten the life of putty. There needs to be a more than just a sliver of putty to seal properly.

    2. Old glass is becoming very difficult to find, and often involves searching reclaim material suppliers. There is an easier answer though!

      We manufacture Old Style Window glass that replicates many of the properties of hand drawn and drawn glass. By taking new float glass and treating it in a kiln, we have developed several types of glass that mimic old glass waviness and imperfections.

      Old Style Window glass is now being used in many new and historical applications. You can see examples of Old Style Window glass on our website, and we ship all over the USA.

  10. Very good informative article! But as you mentioned, if anyone having history windows then I don’t think they can do-it by themselves and if these windows got minor crack then we have to call professionals for better treatments.

  11. Very good informative article! I will try to replace my shed window by following your instructions. Here you can read more about window glass replacement options.

  12. Is it ok to primer (KILZ Complete) the rabbets prior to doing this work instead of using Linseed Oil?

  13. If you have pieces missing and need to cover it, you should cover the broken area with several layers of thick clear plastic, cut to size with scissors. If plastic is not available, a sturdy trash bag can be used. Tape the plastic into place using clear packaging tape. A staple gun may be used if securing the plastic edges to a wooden window frame. Secure the plastic to the outside of an exterior window, if that is a practical option.

  14. Great instructions now I can totally do it with my own by not hiring professional person working with glass and window services

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