How To: Glaze Windows in Place

I get this question all the time, and I’m amazed it has taken me so long to address the topic comprehensively in a post. You’ve been patient enough so today I’ll teach you how to glaze windows in place.

The process for reglazing an old window is something that need to be done about every 30-40 years so if you do it right the first time you may never need to do it again unless you plan to live in that house a long time. The longevity comes from using the right glazing putty and the right techniques. Let’s dive in.

Glazing Windows in Place

Sometimes called glazing in-situ is the process of replacing broken glass or missing putty on a historic window without removing the window from the opening. In a full restoration of a window (learn more about the process here) I always prefer to remove the window sash from the opening and do the restoration in my shop where I have easier working conditions and more control, but it can be done in place.

Tools

• Drop Cloth
• Glazier’s Knife
• Austin’s Glazier’s Putty
• Whiting
• 1 1/2″ Wood Chisel
• 5-in-1 Tool
• Hammer
• Boiled Linseed Oil
• Rags
• Chip Brush
• Triangle Glazing Points
• Fletcher Pushmate
• Razor Knife

Step #1 Chip Out the Old Putty

Setup a drop cloth to catch the inevitable debris from the process. Removing old putty can be a bit messy and the drop cloth makes clean up extremely easy.

Using the chisel and hammer slowly chip out the old glazing putty. You have to work carefully to avoid breaking the glass or gouging the wood, but it can be done. There are some tools that can make the job easier depending on the condition of the putty. If it’s loose then the chisel should be all you need, but some stubborn putties can be softened up using heat from an IR Paint Stripper or similar tool.

If you’re using the IR Paint Stripper then focus the heating element on the putty for about 20 seconds and then using the chisel to remove the softened putty should be easier.

You don’t need to remove all the existing putty, but just the failing loose putty. The new putty will bond to small remnants of old putty. Just don’t try to skim coat the old putty with new because the thin coat of glazing putty will fail quickly.

Step #2 Prep the Rabbets

Brush off any remaining dust in the glazing rabbets. Then using a rag apply a liberal coat of boiled linseed oil to the rabbets to prepare them to accept the putty. Feel free to wipe a couple coats of oil onto the wood if it keep absorbing the oil quickly. This step is pivotal because it prevents the dry wood from sucking the oils out of the glazing putty which will cause early failure. Keep applying until the wood keeps a slightly shiny appearance. This means it has absorbed all the oil it needs.

Lay your oil soaked rag out so it can air dry. Do not ball it up since drying oils like boiled linseed oil generate heat as the dry which can cause the rags to spontaneous combust if they are balled up or thrown in a pile. Read this post about using Boiled Linseed Oil Safely to get a good idea of best practices.

Step #3 Replace Glazing Points

Glazing points are the little metal tabs that actually hold the glass in place. It’s not the soft putty that does this. If all your glazing points are still in place then you can skip this step; otherwise add one glazing point per side and one additional for every 12″ of glass.

I prefer using triangle glazing points for on site work like this because they are easy to install with a Fletcher Pushmate. Press them into the wood tight to the glass and make sure they are pushed in far enough that they will sit behind the edge of the new glazing putty you are about to apply.

Step #4 Apply Glazing Putty

Grab a handful of Austin’s Glazier’s Putty and need it in your hand to soften it up to a workable consistency. Then apply it using your glazier’s knife back packing it into the rabbet. This shouldn’t look pretty at this point. You just want the putty packed in tightly with plenty of putty.

Once you have the putty packed then it’s time to finish glaze a clean line. This is the step that takes some practice to do attractively so don’t be disappointed if your glazing lines aren’t perfect. Practice makes perfect and you can always dig out the putty and do it again until you are happy with the result.

Start in a corner and holding your knife at an angle between the glass and wood apply decent pressure to create a smooth straight line of putty on all sides. Then come back and tune up your corners so that you get a clean mitered appearance of the putty.

Double check your work inside as the putty should not be visible from inside. If you see some putty showing inside then draw a new line a little smaller than your last until you hit the right spot.

Step #5 Clean With Whiting

Once you’re happy with your putty lines then it’s time to clean the glaze of the oils from the putty. Using a chip brush dipped in whiting powder you can brush the glass clean of the oils and also help the putty begin its skinning process. Lightly brush the whiting all over the surface until the glass is clean then brush off or blow off the remaining dust.

Step #6 Finish With Paint

Traditional glazing putty like Austin’s Glazier’s Putty requires painting to last. Once the glazing putty develops a skin on the surface (usually 3-5 days for Austin’s, but some other putties can take weeks) it’s ready for paint. The putty has a skin when the surface feels dry of any oil and a tough feel. It will still be soft enough to get finger prints or gouges if you are rough with it so be careful.

You don’t need to prime glazing putty so 2 quality coats of acrylic or oil-based paint will be all you need. Apply the paint to where it laps over onto the glass by at least 1/16″ to 1/8″. Avoid using tape or razors to cut it back because this causes the paint edge to be broken and causes early failure of the paint to glass seal which is important.

Replacing the Glass

What if you need to replace the glass because somebody broke it? There’s a few more things to do before re-glazing the window but once the pane is replaced it’s the same process. Here’s wheat you need to replace the glass prior to glazing.

1. Remove Broken Glass – Wearing gloves and glasses, carefully remove the remaining pieces of broken window glass and dispose of them safely.
2. Clean Rabbets – Clean the old glazing putty from the rabbets on the outside of the window. Use the chisel or razor 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. 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. Just remember the old saying “Measure twice, cut once.”
5. Bed Your Glass – Add glazing putty to the rabbet. This will create an air tight cushion for the glass to rest in. 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.
6. Set Glazing Points – Set those glazing points we talked about earlier, one per side and one extra for every 12″ of glass size.
7. Clean Interior Glass – Once the glazing points are set, clean the excess putty off the interior of the window where it squeezed out. This should be scraped to a flat line with your glazier’s knife to where you don’t even see the putty.

Once you’ve got the glass replaced and secured with glazing points you can move forward with the glazing process starting in Step #4 above.

You’re now ready. You’ve learned everything need to know about glazing windows in place. Practice will always make your putty look better and better, but even imperfect looking putty will still perform just as good in the long term. Go get ’em and let me know how it goes in the comments below.