If you’re restoring historic wood or steel windows then you’re probably dealing with glazing putty rather than the modern glazing gasket systems. Glazing putty is a wonderfully versatile product that was used for centuries to install glass into the earliest windows. In the 1950s and 1960s it began to fall out of favor and things like proprietary glazing gaskets, caulks, wood glazing, and other options took its place.
I’ve been writing about glazing putty since the beginning of this blog in 2011 and using it long before that so I felt it was time I assembled everything you need to know about glazing putty into one comprehensive post. If you’ve got glazing putty questions this post has all the answers you could possibly want so dig deep and be ready to drink from a fire hose.
What is Glazing Putty?
Glazing putty was traditionally used to seal the individual panes of glass in wood, steel, and to a more limited basis, aluminum windows as early as glass was installed in the first windows. It was heavily in use as a compound that was mixed on site by painters and glaziers when it was common for them to be mixing their own paints before the industrial revolution. Later, it became readily available at paint suppliers and hardware stores.
Glazing putty was traditionally a combination of whiting (calcium carbonate) and linseed oil, though manufacturers would add different elements to achieve different consistencies and effects. Often small amounts of white lead or asbestos were added to putties to give them additional elasticity and improve their performance.
How is Glazing Putty Applied?
Glazing putty is primarily applied using a putty knife. There are some modern glazing compounds today that come in a caulk tube, but these are not in the same league as the traditional glazing putties so I would advise staying away from these products.
Though putty application had slight regional differences, the general best practices were to apply a bed of putty into the glazing rabbets prior to installing the glass which was then pressed into the putty creating an excellent seal against water and air. The excess putty was then scraped away and the glass was secured in place with small metal tabs called glazing points which came in a variety of sizes and shapes.
After the glazing points were installed the face of the glass was puttied and tooled to a smooth beveled surface that seals the glass and allows water to shed easily off the surface. The corners of the putty are tooled into a mitred joint which gives the look of wood joints.
After several weeks or days, depending on the glazing being used, the putty has cured enough to be painted and sealed against the weather which extends its life and protects it from the elements.
What’s the Best Glazing Putty?
This is a tough question because it’s largely a matter of personal preference, but there are some characteristics, undoubtedly, that make for a quality glazing putty. To rate a glazing putty you need to look at the following characteristics.
- Ease of Application
- Clean Up
- Cure Time
- Mildew Resistance
- Long-Term Performance
Below I have listed some of the most popular putties available today and given you a description of each as well as a combined rating based on my experience working with each.
This is the most common glazing putty that professional window restorers use. It is relatively easy to use, not too oily, or too dry and tools to a nice smooth finish. The putty is also fast to skin over, which means it is ready for paint (in most conditions) in as quick as 3-4 days. It is only recommended for glazing in a shop, which simply means it must be painted prior to be exposed to sun and weather. It is only for wood sash (not for steel windows). Despite this, I have had decent success using it sparingly outside as long as I get it painted in the 3-5 day range after application.
Scott’s Rating (1-10): 9
This is my personal favorite glazing putty. I partnered with the Sarco Putty Company to formulate this putty years ago to meet my exacting specifications. This putty is essentially Sarco Type-M putty with the addition of non-toxic, mildew inhibitors. Glazing windows in the humid southern US we struggled for years to keep mildew off our putty (a common issue) and after 3 years of development we found a formula that worked. The putty is easy to tool, cures quickly in 2-3 days, and can be used on steel windows, as well as for in-situ glazing, making it the most versatile putty on the market today.
Scott’s Rating (1-10): 10
This is the first putty I learned to use because it can be used almost anywhere. It is designed for wood OR steel windows and can be applied outside or in a shop. This makes it a good choice for spot glazing touch ups outside. Dual Glaze is similar to work with as Type-M, except that it’s a bit oilier which makes it a little messier to work with, especially on hot days. The downside is that it takes a long time to cure (2-3 weeks). But that slow curing makes for a putty that stays flexible much longer than most of its competitors. That flexibility and the option to leave this exposed to the elements for months provides a nice option for people not wanting to paint immediately.
Scott’s Rating (1-10): 8
DAP 33 is available at almost every hardware store, which is one of the reasons I think so many people use it. I used it sparingly at the start of my business since it was easy to find. I found it very greasy to work with and difficult to get a clean line unless my putty knife was constantly cleaned. The curing time until it was skinned over and ready for paint was closer to Dual Glaze in the 2 week range, though in cooler temperatures it has taken over a month or two, which was one of the reasons I quit using it. In general, I’m not a fan of this putty and think it is the reason most people find glazing so tedious.
Scott’s Rating (1-10): 4
Production of AquaGlaze has recently been stopped, but I’m not sure if that is permanent or temporary so I feel like it’s still worth discussing because it’s such a unique glazing putty. Unlike the other oil-based putties, so far, Aqua Glaze is an acrylic glazing putty. The thing that makes Aqua Glaze special is its super fast curing time. It can be ready for paint in as quick as 1 hour! This can be a big help if you are in a time crunch. Of all the putties here, it is probably the most temperamental to work with. It has to be mixed thoroughly before being used, otherwise it can be pretty sticky.
Scott’s Rating (1-10): 6
I tried a gallon of this at a friend’s urging and found that it works rather well. It has been around long enough and has been tested enough that I feel comfortable putting it on my windows too. Glazol seemed to me to be somewhere in the middle of Type-M and DAP 33 in terms of it’s workability. It was ready for paint in about 4 days which was great, but it was a little chalkier than I was used to. So with the better options out there it’s not something I plan to use.
Scott’s Rating (1-10): 7
Possibly the most traditional of all these putties is the Allback. If you want to be true to the old school ways, this is glazing putty in its purest form. It’s made mainly with whiting and a purified linseed oil that has had the proteins removed (this helps fight mildew). Allback putty is pure as the driven snow. The biggest advantage of this putty is that it can be painted immediately but only if you use a linseed oil paint, which can be a major time saver. The down side is that it is expensive and I have found it to still mildew even if the mildew is less prevalent than other putties.
Scott’s Rating (1-10): 7
I’ve seen this putty on the shelf at my local Sherwin Williams store and have wondered how it performed, so I forked over a few bucks and brought a quart back to the shop for testing. The putty is white in appearance just like DAP 33 and when I dug it out of the container, I found it to be a sticky, gooey mess to work with. It stuck to everything, including my gloves so much so that I had to take them off and use my bare hands. The stickiness did make it easy to adhere to the glazing rabbet but other than that, I did not enjoy working with this putty one bit. Trying to tool a smooth finish was not an easy task and I’m a pretty good glazier. Cure time was about 13 days before it was ready for painting. Even if this putty performs amazingly, I would not recommend it because it was such a pain to work with.
Scott’s Rating (1-10): 3
This is a linseed and calcium carbonate putty with titanium added. It’s a natural product with no harsh chemicals and very similar to the traditional putties of the old days. The putty comes in a sealed metal can and has a layer of water on top to prevent curing in the can. The water keeps the oxygen off the putty and prevents it from developing a skin on top which saves you from loosing a layer of cured putty, which is nice. Right out of the can, the putty was simple to work in my hands and tools pretty nicely. I didn’t have any problems with the putty sticking or clumping and it was easy to work. As far as the cure time, I was impressed that after only about 1 week the putty had developed a good enough skin that it was ready for paint.
Scott’s Rating (1-10): 7
How To: Make Your Own Glazing Putty
The commercial putties on the market are a little better than homemade recipes and always more consistent, but the homemade stuff can work great when you just need a little batch. Or maybe you are one of those hardcore DIYers who like to make everything yourself. Either way, it’s a fun project to make your own glazing putty.
Glazing putty doesn’t keep forever, so just make a batch large enough to handle what you plan to glaze in the next week or so and then make some more if you need it later.
Traditional linseed oil putty was made from only 2-3 items.
You can find linseed oil at most hardware and paint stores. Using boiled linseed oil will result in a faster curing putty, whereas raw linseed oil putty results in a longer lasting flexibility with the putty, so, there is a trade off. Whiting is a little scarce these days, but I do sell it in my store if you can’t find it locally.
You can also add Zinc Oxide to help control mildew growth on your putty if you live in a region that is particularly hot and humid like we are down here in Florida. I find that adding about 1/3 cup of zinc to 1 quart of putty to be helpful.
Mix some linseed oil with the whiting until you get to a workable consistency like Play-Doh or if you are a baker, actual dough. The consistency of your putty is completely dependent on your preferences. You may want it softer or firmer depending on your needs.
Personally, I have found that the best consistency for glazing with a putty knife is thicker than you initially think. The putty should be firm enough that it won’t slump or sag when rolled into a ball.
Mix the two together in a bowl or other container to initially blend the ingredients. Eventually, you will have to pull it out and spread it on the table to knead by hand like a baker to get it all mixed thoroughly. Knead the putty and work it until it is a consistent texture throughout.
How Long Does Glazing Putty Last?
Other than the type of glazing putty you use, which plays a major role in how long your putty will last, it really depends on a few factors some of which you can control and others you can’t. It can vary from as little as 5 years to as long as 50 years. Below are some of the major factors affecting putty life.
Hot climates and especially windows with heavy sun exposure will have a significantly shorter life for glazing putty. If you’re in the northern US you can expect the average window to get 20-30 years of life before it needs to be reglazed with new glazing putty. Down here in Florida, I have found that glazing putty has an average lifespan of only 10-15 years.
Are your windows under a porch covering? Do they face south or west were they get more intense sun? Just like paint, glazing putty lasts longer when protected from the elements, especially the sun and heat. Windows on a porch can have glazing putty that can last as long as 40-50 years in some cases that I have seen.
This factor is entirely up to you. Keeping putty painted and clean will greatly extend its life. Glazing putty needs to be sealed with a paint line that laps over the putty onto the glass in order to perform its best. This paint line often fails, allowing water to get behind the putty causing premature failure. Keep it painted to get a longer putty life.
Why Does Glazing Putty Crack?
Glazing putty has a tough job to do. It has to bridge the gap between two very dissimilar materials (glass and wood), which move at very different rates. Glazing putty is slowly curing over many years. Oils don’t dry, rather they cure, and that curing takes a long time.
As the oils cure the putty becomes harder and harder each year which makes it less effective at withstanding the constant expansion and contraction of the wood.
Eventually, the stress becomes too much and the putty begins to crack. Those cracks allow water to get in behind the putty speeding up the failure. Eventually the putty comes loose from the wood and glass and needs replacement.
You can slow this process down by keeping the putty painted and replacing any damaged or missing sections promptly.
Can You Repair Glazing Putty?
Yes, glazing putty can be patched and should be as a part of its maintenance cycle. You don’t have to fully remove the sash to re-putty it. The work can be done on site if you’re using an appropriate glazing putty like Dual Glaze or Austin’s Glaziers Putty.
New glazing putty will bond to old putty as well so it’s not necessary to remove every ounce of putty, but a good portion should be removed prior to re-glazing.
Avoid skim coating old putty with new glazing putty. A thin layer of putty will fail very quickly and will usually appear unsightly from the inside of the window.
The video below will show you the process of repairing glazing on a window in place.
How To Remove Glazing Putty
Whether it’s steel windows or wood windows, removing glazing putty is one of the more frustrating things to do in my opinion. How hard the work is depends on a lot of factors, like how old the putty is and what type of putty was used. There are a few tricks to remove glazing putty without breaking the glass that I can show you.
Mainly, it comes down to being patient and careful. No matter which technique you use, remember that you are working with very thin glass that doesn’t require much force to break.
Also hiding underneath the glazing putty are a variety of metal glazing points which hold the glass in place. These are a big source of broken glass when being to aggressive so watch out for them. They come in various forms and below is a picture of some of the most common shapes you’ll encounter.
Option 1: Chisel & Scraper
I’ve tried probably more than a dozen different tools and techniques to remove glazing putty, but it often comes back to the old standard. It’s not sexy or exciting or new, but for removing anything from cement putty to caulk, a good chisel can work wonders. And it’s super cheap and portable!
I like to run the chisel along the joint of the putty and the glass first. It usually takes a few passes, and with each successive pass, you’ll dig a little further between the putty and the glass, breaking that seal. Don’t try to get it in one pass, or you will likely break the glass. Take your time and work it a little bit at a time.
Once you’ve got the putty and glass separated, then move to the joint between the putty and the wood. Be extra careful here to not gouge the wood. Other than breaking glass, this is the most common issue with using a sharp chisel on a soft wood sash. Again, go slow and work methodically. Eventually, the putty will begin chipping or peeling off in chunks.
After the chisel has done its work, I use a ProScraper to scrape the rabbets clean of any excess putty so that the glass will come out smoothly and not get caught up on any trouble areas.
Option 2: Steam Heat
This is what I use in my shop to remove glazing putty. It’s fast, clean, and very effective. Not to mention, it keeps the dust down and that helps us work lead safe. You can use any standard clothes steamer like a Jiffy steamer and do spot work, or you can build a steam box (learn how here) pretty inexpensively. If you plan to do a lot of windows, a steam box is absolutely the way to go. For one or two windows, the chisel and scraper is the best.
After an hour in the steamer, the glazing putty is softened up and comes off much easier. It also comes with the added bonus of helping removing the paint in preparation for restoration. Check out my video of how steam glazing removal works below.
Option 3: Infrared Heat
It’s so much more than plain red, it’s…INFRAred! Seriously though, infrared heat is a great way to remove glazing putty. Like steam heat it helps to soften the putty and make it more pliable so that you can scrape it off with something as simple as a 5-in-1 or putty knife.
My preferred infrared heater for glazing putty on most sash is the IR Paint Stripper which is the most affordable infrared tool on the market. For very intricate sash with small pieces of glass a better option would be the Speedheater Cobra which can fit into smaller areas more easily.
I place aluminum step flashing over the glass to protect it from the heat, otherwise you will end up with broken glass due to the intense heat. Just a few pieces that you can move from one section to another is enough to protect your glass.
When using any kind of infrared or even regular heat guns, be careful to keep moving. Don’t leave the heater in any one location for too long or you may end up burning the wood and paint. It doesn’t take much heat to soften the putty, so start with short 10-20 second bursts and gradually lengthen it out if necessary.
Do You Need to Prime Glazing Putty?
To prime or not to prime, that is the question! This is a topic that creates a lot of disagreement in the historic window community. Different putty manufacturer’s have different requirements, but most traditional oil putties like Sarco, Austin’s, and Allback do not require or even recommend priming the surface of the putty before painting.
Dap 33 is the outlier here as the manufacturer recommends priming with an oil-based primer if you plan to top coat with an acrylic paint, but if you are top coating with an oil-based paint then the primer is unnecessary.
Prime the Rabbets?
Before you put any putty on a bare wood sash it’s recommended that you seal the rabbets with either an oil-based primer or shellac. Both of these were traditionally used and for good reason. Bare wood, especially old dry wood will suck the oils right out of the putty causing it to dry and shortening it’s life considerably.
Priming any bare wood in contact with putty is the best way to seal the wood and keep the oils in your putty. Shellac is a good option if the window is going to be stained to avoid any primer showing getting into the stained and varnished sections.
How Do You Clean Up Glazing?
The oils from glazing putty, typically a mixture of linseed and soybean oils will dry quickly on glass in just a couple hours so it’s imperative to clean things quickly. As soon as you’re done glazing your window you need to clean the glazing putty with whiting to prevent residue on the glass.
Grab a soft bristle paint brush and a container of pure whiting. It’s best to dedicate and paint brush to this purpose and plan on not painting with it again due to the putty and oils that can build up on the brush over time.
Step 1 Apply Whiting
Sprinkle a couple teaspoons of whiting onto the glass and spread it out onto the face of the glazing putty and all over the glass.
Step 2 Brush Vigorously
Using that soft, old paint brush, brush the whiting vigorusly across the surface of the glass and along the surface of the putty. Be careful to have a light tough around the putty to avoid gouging the putty. Keep brushing until the glass comes clean of residue. This will also absorb the excess oils on the face of the putty which whill accelerate the skinning process that needs to occur beforte the putty is ready for paint.
Step 3 Reclaim The Whiting
The excess whiting can then be brushed off the window and even though you won’t get it all back into the container you can save and reuse any that you can finagle back into the container.
Step 4 Clean Remaining Dust
Any remaining whiting on the window can be gentle brushed off the window or blown off using compressed air. Once the glazing putty has cured, usually 3-5 days for Austin’s Glazier’s Putty which is what I use, you can wipe the whole thing down with a damp cloth before painting to seal your glazing putty.
The key is to act early. If you wait more than a few hours or let it sit overnight then this quick trick won’t work and you’ll be left scrubbing and cleaning with a razor blade to get that residue off. Be sure to leave yourself enough time for cleaning glazing putty when you finish glazing your window and you’ll be in much better shape next time. Check out the video below to see how it works.
Can you Tint Glazing Putty?
Yes, you have a couple options when it comes to tinting glazing putty and any of them work well.
First, you can buy putty that is tinted from the factory. Mainly, this is an option for Austin’s Glazier’s Putty which is available in grey (natural) or brown putty in quantities as small as quarts and gallons. For larger projects, Sarco also sells tinted glazing putty in grey, brown, or black, but you have to buy a full batch which is typically 20 gallons or more.
Another option is to add dry pigments to your glazing putty before glazing. You can make almost any color with this option and can fine tune the color very precisely, which may or may not be necessary.
Freshly glazed putty can also be stained using an oil-base stain. This liquid stain can be mixed in just like the dry pigments before glazing or applied after glazing the same way you apply stain to wood. Just be sure to apply the stain before the putty has skinned over otherwise you won’t get good penetration into the putty and the result will be blotchy.
What is Cement Putty?
Cement putty is a real thing and it is more common on steel windows than wood windows, but it can show up anywhere. There are some putties that, once fully cured, are as hard as a rock and are completely immune to steam, infrared, chemicals, or anything else.
These were glazing putties that were mixed with portland cement. They are annoying and unpredictable as to where you will find them, but when you do, there is only one thing to do and that is to break out the chisel. It dulls chisels and is exactly like the name implies, hard as cement, but it will come out and it can be restored with new putty that won’t turn to stone.
That’s it! But maybe there is a question I didn’t cover in this post, though I can’t think of it. Let me know in the comments below if there is something that I missed about glazing putty.
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I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.