Ask the Builder: Restoring a bathroom window sash
A fellow amateur radio operator sent me a photo of a wood window in his girlfriend’s bathroom. The window is suffering from rot, and the sash frame is starting to separate.
While I don’t have the epic enhanced observation powers of Shawn Spencer in the TV series "Psych," I was able to determine by looking closely at the photo what caused the issue.
When I looked closely at the photograph, I could see a depressed part of the sash profile in the lower right corner. Water vapor from hot showers no doubt condensed on the glass pane, it then rolled down the window, and finally found a tiny crack to enter the wood at the sash corner.
I would guess that the problem has been going on for some time, and the weight of the glass pushing down on the lower, horizontal sash frame caused the two pieces of wood to separate at the corner. As the crack got bigger, more water entered faster and deeper, accelerating the rot.
Fortunately, this sash can be salvaged with a small amount of effort. Jeff may prefer to wait for warmer weather to do the job, but he can start a repair in the winter if he has the skills to cut a piece of plywood the same size as the sash so he can pull out the damaged sash to work on it. In warm weather, I’d just use a piece of thick cardboard to close up the opening while repairing the sash.
The first thing that needs to be done is to clean the mildew off the sash; a fan should be used to dry the wood at the corner. Once the wood is fairly dry, I’d use a long squeeze clamp to see if a moderate amount of pressure will close up the gap between the two pieces of wood that make up the corner.
Just in case the corner can be drawn tight with the clamp, I’d squirt some yellow carpenter’s glue in the crack and use a popsicle stick or other thin piece of wood to spread it around in the crack. I’d then start to tighten the clamp hoping the corner draws up tight. If it does, I’d leave the clamp in place for a few hours.
I’d place the bottom pad of the clamp about 1 inch from the outside corner of the sash. I’d want to be able to drill a pilot hole in the bottom of the sash about 1/2-inch from the outside corner so I could install a 3-inch-long stainless-steel wood screw up through the horizontal sash frame member into the vertical frame member while the clamp is in place. Carefully drill the pilot hole so the screw stays centered in the wood frame.
If the corner can’t be drawn tight with the clamp, the crack can be filled with wood epoxy. I’ve got two videos at AsktheBuilder.com that show how to mix, apply and sand this wonderful material.
Another option is to replace the window, but this is likely to be costly. A year ago I broke the glass in one of my own up-down sash wood windows while cleaning it. I discovered it would be cheaper to buy a new sash from Andersen Windows than to go to all the hassle of ordering a custom insulated glass pane, removing the broken glass, installing the new glass, and then trying to match the custom exterior color.