Fixing Broken Window Panes

A carpenter discusses the finer points of how and when to replace a window pane.

Posted by Kevin Stevens | Mar 24, 2011
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lizevans/stock.xchngWindows these days can be pretty high tech, it is not uncommon to see double and even triple paned window filled with Argon and coated with special materials to limit heat gain, or reduce heat losses. The days of a simple sheet of glass set in a wooden frame with glazing points and  putty are rapidly fading into history. If your have a broken pane, the fix can vary from “simple” to, “I’d better call in the pros.”

A few months ago I got to repair a broken pane in a client’s window. This window was an old architectural gem that was being used as an interior window to let light into the guestroom from the main living room area. It was easily 50 years old and was of the traditional single pane, points and putty configuration. Repairing a window like this is pretty straight forward and involves these basic steps:

  • Its easiest to work on a window that in not installed.  The first step, if possible, is to remove the window from its installed location. Many older style windows can be removed by popping off some narrow strips of molding or trim that hold the window sash in place.
  • With the sash removed, the next step is to take out the broken glass. This should be done with some sturdy leather gloves and safety glasses. Something more than good intentions should separate broken glass and its sharp edges from delicate skin. Chances are the old putty is dry and brittle, so a stiff thick putty knife is helpful in removing it.
  • Buried in the putty you will find a number of glazing points. These can be simple triangles of metal or the spike type with a “L” shaped shoulder. A set of needle nosed pliers, or a thin screwdriver, can be used to pull these out. The role of these points is to hold the glass in the window frame.
  • Once the points are removed, the rest of the glass can be lifted out. If this pane is somewhat intact, it can be used as a template for the replacement pane. Basic squares and rectangle are pretty easy to measure arcs, curves and circles are a bit more complex, and here a template can save lost of time and energy.
  • Now that the glass is out you will need to remove the thinner layer of putty that was below he glass. This layer usually comes away at lot easier than the top layer you worked through to get to the points.
  • With the pane removed and all remains of glazing putty removed, now is the time to correct any minor damage to the windows frame. Excessive gouges in the wood, cracks, etc. should be fixed. A little glue or wood filler often makes quick work of this. A little touch up paint or varnish can be applied to these bare surfaces to ensure their longevity.
  • To reinstall the new pane, a thin “bedding” bead of glazing compound is applied to the frame and the glass is set in place.
  • With the glass pressed into place install new glazing points are used to keep the pane seated in place.
  • A finishing layer of glazing compound it then set above the points and beveled with your putty knife to provide a nice smooth transition from the window frame to the pane. This is often the tricky part, as getting a nice looking surface takes a bit of practice. Don’t worry too much -- glazing putty is slow to dry so you can keep working it until you get a smooth finish.
  • Once the putty is in the window sash can then be re-installed. After a drying period the glazing compound should be sealed or painted to protect it from the elements if so exposed. This drying time will vary based on your climate and temperature and can run into weeks. Keep checking to see when it is ready.

Double Pane “Modern” Windows

The above steps work great for the older single pane style windows. But these are becoming pretty rare in homes. Chances are your windows are more modern, energy efficient and a bit harder to repair. I have repaired some windows that were set in wood or metal frames that allowed disassembly and re-assembly. Here a pane is often set with a gasket in lieu of the older putty. Screws or moldings allow the pane to be removed and re-installed. If your window falls into this category, its still a viable DIY project. Depending on the how the sash or panel in configured this can sometime be a bit easier than the old putty installs.

Sash Replacements

Many windows today are built from “welded” vinyl and therefore are beyond the reach of most DIY homeowners’ skill sets. In these cases it is normally required to replace the entire sash or in extreme cases the whole window. These windows are often on the lower price scale, and easy replacement is one of the sacrifices made for this cost advantage. 

Some window replacements do not involve broken panes, but merely bad or broken seals. In the near 20 years I have been in my home, I have replaced a few of the large panels in my sliding doors. In these cases, I removed the slider or fixed panel from the door and took it to my local glass company. They quickly (one-day turn around) replaced the pane and I re-installed the panel or slider. This “partial” DIY repair saved me the cost of travel and field costs…which in many jobs can be 50% or more of the cost. Parts and labor for one of my sliders was less than $150, and obviously transporting a 30” x 80” window is not available to many homeowners, so in those cases its best to call in the pros to complete the whole job.

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