Top 6 Window Restoration Mistakes

I’ve been doing window restoration for over 15 years at this point and I can assure you that just like anyone who picks up a putty knife I have made every one of these mistakes (and many more!) over the course of my career.

In the interest of helping you avoid the same mistake I made in window restoration I thought I’d share the top six window restoration mistakes. Please learn and avoid these mistakes at all costs. Let’s dive in.

1. Picking the Wrong Putty

Picking the right glazing putty was like shopping in the cereal aisle with your children. This one looks fun, but this one is healthy. Do I want oats or corn or rice? The confusion is real and everyone has an opinion that they consider a fact.

Just like cereals there are some glazing putties that should NOT be on your list. I’ve gone deep on glazing putty in this post if you want to learn it all, but if you’re the TL;DR folks like I am sometimes here’s the quick and dirty of it.

Don’t use anything that comes out of a caulk tube or DAP 33. How’s that for simple? You need a knife grade putty rather than a caulk to make your window perform well and look right. You also want something that doesn’t take an eternity to cure like DAP 33. It’s almost like the folks at DAP thought, “Hmmm, is there a product we can create to make all window restorers want to stick their putty knives directly in their eye?” and thus DAP 33 was born.

There are lots of good options on the market. Sarco putties like Type-M and DualGlaze are excellent options as is our in-house putty (also made by Sarco) called Austin’s Glazier’s Putty. They are easy to work with and cure in short order leaving you with the prettiest old windows.

2. Using the Wrong Wood Filler

The first job I did I used something called Durham’s Rock Hard Putty. It lasted exactly eight months before the door I patched rejected the wood filler like my high school girlfriend did to me 1 week before prom and it was equally as painful (well, almost).

This is another topic I have done a lot of testing on and you can read the results of my testing in my older post about wood fillers and epoxies as well as in the video below. But again in the interest of being succinct here’s my general rule of thumb.

Wood filler works fine for filling nail holes, easy breezy. For larger sections of wood don’t use anything other than a true wood epoxy. And, no, Bondo is not a wood epoxy. Whatever you use, don’t fall for the allure of Bondo. Bondo is an auto body filler and patching old-growth wood is a lot different than sheet metal.

Epoxies like the ones made by Abatron are my favorite because they are just so easy to use. West Systems and Conserv also make good epoxies for historic windows. Stick with these and you’ll have longer lasting patches and happier clients.

3. Sizing the Parting Bead Wrong

If you enjoy banging your head against a brick wall without a helmet please skip this section.

Cutting the wrong size parting bead is, IMHO, the quickest way for an install of window sash to turn from a joyous event to a day or terror and dread. Parting bead is typically 3/4” x 1/2” and I use the word typically very loosely here. These old houses have sooooooo many slight variations in size of parting bead that you need to be prepared to modify or mill your own for each project.

As a quick aside, my store sells parting bead in pre-milled sizes but you can also request a specific size and we will make it exactly to your specs at no extra charge if you’re interested in a helping hand with this part.

Even a difference of 1/16” can make your parting bead refuse to fit into the rabbet on the jamb leaving you banging away with no victory. Or if it’s too small then it flops around in the jamb like a fresh caught fish on the dock.

Here’s how you avoid this: Take a piece of the original parting bead and match it. Not make it close…MATCH IT! Also keep in mind that if you match the size of the original parting bead and then you apply a coat of primer and 2 coats of paint to your parting bead before installing it is no longer the same size as the original. You just made your parting bead too thick and you’re going to suffer greatly.

4. Not Bedding the Glass

Let me tell you a little story. I have always noticed that some old windows had a thin layer of putty separating the glass from the sash (called bedding) and some did not. I didn’t think much of it at first until I was stuck by a spell of hubris (n: excessive pride of self-confidence). I decided that I could offer clients a cheaper version of window restoration that didn’t include the bedding putty. Prices would go down, profits would go up and I would save the world. This did not occur.

What happened in this two-year experiment is that I had more pieces of broken glass both during the restoration process and months after because there wasn’t this pillowy cushion of bedding putty in my windows. Then the rainy season in Florida came and I was deluged with calls about water leaking around individual panes of glass.

I call this experiment my “Bedding Degree” from the school of hard knocks. Can you get by without bedding your glass in putty? Possibly. Would I ever do it this way again? Not a freaking chance.

5. Breaking the Glass

Listen, glass breaks. I hate it and every time it happens it’s like the opposite of It’s a Wonderful Life’s famous line. “Every time glass breaks an angel loses his wings.”

Sometimes there are micro-cracks you can’t do anything about, but most of the time glass breaking is your own fault. You’re rushing or being too aggressive. Here’s how you can avoid it:

Take your time. Go nice and slow, don’t rush, and be gentle. This is good advice and I have a feeling most guys have heard this before. You just need to apply this in the window shop too, right ladies?

Also, despite the fact that you often can’t see them there are ALWAYS glazing points hiding under that putty just waiting to spite you. Once I have all my glazing putty out I will slide a 5-in-1 around the edges inspecting for glazing points. I then use a sharp chisel on its side to pry them out from the wood before I even attempt to remove the glass.

Try these tips and you’ll be in far better shape with far less glass breakage.

6. Not Securing the Ropes

When I first saw the ingenious design on the side of a double-hung sash I was amazed. There is a perfectly sized mortise to hold the rope knot in place. How clever! I thought, “That’s all it needs, there’s no chance that rope will ever slip out.” Then the moment I installed the last nail on the stops it would slip out and I would have to pry off the stops and redo the whole thing.

Don’t fall prey to this major time suck and annoyance. Ropes slip out despite our best intentions, so what can we do? It’s this ingenious little thing called a nail. If you prefer a screw then by all means try that, but nails work best for me. Here’s what I do:

I use 1 1/4” 18 ga. nails to attach my interior stops so I’ve got my nailer ready to go, and once the rope is secured in its little home in the side of the sash I shoot one “insurance” nail into the side of the rope just above the knot to secure it in place.

It’s easy for the next guy or girl to remove and it holds the rope in place using the existing tools I already have in my belt. Problem solved.

Final Thoughts

I really hope you can learn from these window restoration mistakes of mine. I could probably have written a post about the 40 worst mistakes of window restoration because I’ve made so many over the years, but that might be a bit of overkill.

Just remember that failing or making mistakes is just an opportunity to learn and improve and iterate anew. Don’t let your failures get you down. Pick yourself up and get back to it because the world needs more window restorers.