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Last Updated: , Created: Saturday, January 10th, 2004

Repairing old fashioned wooden framed windows

Whether you still have some of those old storm windows, or have single glazed windows used as decorative dividers between rooms inside the house, you may need to know how to work with window putty.



In ancient history, the old putty was generally removed with a carpenter's chisel.  But that also broke a lot of glass.  If you are trying to remove hardened thermo plastic caulking, life is even more difficult.

There is one DIY tool made for this task, and it works fairly well -- the Prazi Putty Chaser.  This tool mounts into an ordinary electric drill and has a router type of bit on the end along with a handle and depth guide.  The depth guide rides along on the wood of the window frame and controlls the cut into the hardened putty.  This is slow, but saves replacing a lot of glass.

An oscillating tool can help in that it has saw teeth that can be controlled to not dig into the glass.  For window putty it is best to use the HSS blades and clear out the teeth regularly with a wire brush to keep it from overheating.  The more aggressive blades with larger teeth would be more likely to scratch the glass or plunge right through the wood frame.  The scraper blades with no teeth are really made for digging into soft caulking, not rock hard window glazing.  

Hot air guns are often recommended, but it is very easy to break the glass with those.  Actually hot steam is much better in that it penetrates the putty and softens it up enough to simply scrape it off with a putty knife while having less chance of overheating the glass.  If you have a lot of windows to do, you may want to build yourself a simple home made steam stripping chamber to soften up both paint and putty.  Follow this link for how one Ottawa contractor who workes in heritage restoration has perfected removing ancient window glazing.  



Once the glass is removed you can use a paint scraper to clean off all remaining putty from the frame. It is a good idea to prime paint all of this area before putting the glass back in, as this is the best way to protect the wood and the putty will stick better as well.

If you need to replace a piece of glass, cut a piece of cardboard to fit perfectly into the frame and either use that to cut the glass yourself, or take it to the glass store where they can make an exact copy, complete with any strange angles you may have in that old frame.



Here you see me using the putty knife to push in 'glass points'. This particular type of glass point has ears that stick up, which can be caught by the putty knife. So you can simply put the putty knife flat on the glass and push the point into the wood.  The professional will shoot flat triangles out of a special nailing gun -- much like staples. These points are great for windows and picture frames because they are so easy to install and can be found in all renovation centres. 

Why not nails?  Nails apply a "point" pressure on the glass and can cause it to suddenly break with changes in temperature.  Glazer points have a flat metal face in contact with the glass.



Many people take the easy way and simply use caulking to install glazing.  That is not really a good idea as it is very hard to remove years later -- harder than getting that old glazing putty off.  Glazing putty is a very oily material and it used to be readily available in little packages just the right size to kneed one package at a time.  If you put real glazing putty into a caulking tube, one end of the tube would be oily while the other hard -- you can't mix in a caulking tube.  So if you really want real glazing putty, that matches and works best with those old windows, you will probably have to buy it in a little over 200mL size, a US quart. 

I recommend that with great difficulty you stir in any floating oil, then dump the whole thing out on a clean plastic surface (that will not absorb the oil) and then proceed to KNEED it like bread dough. If you manipulate it a bit before kneeding and then after kneeding you will totally understand why I insist on kneeding your putty -- and you will discover that properly kneeded putty is a pleasure to apply and smooth out.  After kneeding the whole bucket -- getting an even distribution of the oil -- put it back in the bucket and take out only as much as you need at a time. 



The key to getting the putty to stay put is to use a flexible putty knife, or spatula, and force it into place with a very low angle which puts a lot of pressure on the putty.  This doesn't scrape the putty off, but forces it down and the excess comes out the sides. Simply come back with the knife and scrape up the excess from each side. A quick wipe with a finger to seal the edges and the job is done.

So how do you get from the bucket to under the putty knife?  The beginner will take some putty in their hands and roll it into a long thick cord, which they then place on the window frame -- then go over it with the putty knife.  The more advanced applicator will put a large wad of putty in the palm of their secondary hand and with the fingers, pull a fat string forward from the palm to the finger tips, feeding this continuously just under the putty knife which is being drawn along firmly with the dominant hand.  This permits varying the quantity of putty to be sure that there is always more than enough under the knife -- one single pass and its done.   I know -- I need to make a video of that! 

Some putty can be an iritant to the skin so you may want to do all of this with thin rubber gloves.  Read the label on the can.


Keywords: Caulking, Antique, Glass, Putty, Frame, Windows, Heritage, Techniques, Tools

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