This week’s Ask The Craftsman question comes from Mike.
“When reglazing windows, do you have to remove all the old putty or will new putty bond to the old putty?”
Mike, it can be a real chore removing every ounce of old putty when you restore a window and the truth is that not every little bit has be taken out.
You can patch in new putty on top of old putty as long as the old stuff is still adhering well.
We call this spot glazing and here’s how you do it:
Using a putty knife or 5-in-1, dig out as much of the old putty as possible. Leave the really stubborn stuff in place. Blow off any remaining dust after you’re done, then wipe the surface with a little bit of Boiled Linseed Oil and apply your new putty. Clean off the excess oil from the glass with a little whiting and you’re done.
The real challenge is keeping your new putty lines from being too big that they are visible from the window’s interior. This won’t cause any performance issues, but big fat putty beds aren’t very attractive.
Don’t forget to paint your fresh putty as soon as it develops a skin.
Good luck with the windows!
Founder & Editor-in-Chief
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.
Hey Scott – thanks so much for this advice. I’m pretty confident I have removed all the putty that can be removed, exposing quite a bit of the metal window. I plan to prime (with oil-based) the metal – any worries if I get the primer on the old glaze before delicately patching with new glaze? Also, read online advice that Sarco Dual can be tinted with FeO2 to color it dark, which I plan to do unless you say otherwise. We’re going to paint the casement windows a deep charcoal color. Thanks!
Hi Scott,
I am tackling a house full of metal casement windows. The current putty is very old, cracking and chipping. It is powdery in some spots. I believe the putty is original-circa 1950. Do I need to have the old putty tested for asbestos before starting to remove it?
Hi Scott, I’m going to be using Sarco Dual Glaze, which is BLO-based, to fix the glazing on my windows. Do I still need to wipe some BLO on the old putty in order for the new putty to adhere, or will the Sarco Dual Glaze be OK for me to add on top by itself? (I have metal-framed casement windows). On most windows I’m going to be glazing entire lines, but there are some where I need to just add some on top or in between the old glazing. Thanks for your help! –Dave
A little BLO before you apply will help the old putty from sucking all the oil out of the new. I would definitely do it.
OK thanks!
What if the old putty has been painted? Should I sand it a bit to expose the old putty before I lay on new putty?
I’d like to know the answer to this to. Do I need to remove some or all of the paint from the putty? The putty is firm and not lose
Is it boiled or raw linseed oil you use to put with old putty to make it pliable to use again thankyou
Only use boiled, raw will never dry!
What if I am reputtying metal Frames, do I still need oil’s or just leave
I had just completed my first window restoration BEFORE I found your site.
The glazing I had used states it can be painted is 2 days. I had waited 4 days then painted with a water base.). The paint failed and did not adhere, Do I need to just remove the glazing and start over?
Carol, sadly that sounds like the case. Make sure the putty has a skin over top of it and doesn’t feel oily before you paint. No matter what the manufacturer says paint won’t adhere if it’s still oily at all.
My company is old school, I was taught early to use the proper materials and procedures. Your right Scott about the boiled Linseed oil, but cut 50-50 with thinner to help it penetrate into the wood. Window glazzings are not all the same, we use an oil base putty and “do not paint the wood” so the oils in the putty raises the fibers of the wood and when they dry this is were the bond occurs Also use ONLY oil base paints on your windows both primmer and finish. Oil base will penetrate the wood and protect from Dampness inside and out. Latex/Acrylics paint are water base they sit on the surface and also cause mold. These paints don’t seam to dry completely on muggy days the Latex/Acrylics bond back to each other, case in point doors that seam to have swelled in Summer! Spray a bit of Pledge furniture polish on the sticking doors and all that swelling goes away! It’s the paint!
Thanks Scott, for doing it right!
I’m wondering if you can help me know what to look for to determine when the new putty has “formed a skin”. I’ve had new putty curing for 4 weeks and it still feels a soft. I don’t want to dig into it with my fingernail to see if there’s a skin and well… what now?
Lisa, the putty will likely remain soft for a long time (months) but the skin should form in a few days or weeks depending on the putty. If the surface feels firm and isn’t oily then likely it has skinned over and is ready for paint. Think of it like a cake that when it begins baking it first forms a skin while the insides are still liquid. That’s when it’s ready.
The putty is Sarco Dual Glaze. I know that’s a longer one to skin over, so I have been extra patient. 😉 Your answer helped a lot. Thank you!