By Bill & Kevin Burnett
Q: Our house turns 100 this year. We have some dry rot on the exterior of the wooden window frames and windowsill. Does one dig it out and fill with a special concrete? What are the options and what do you recommend? Also, is there anything special we should do when we repaint the repaired area?
A: Congratulations! At 100 years old, a house well cared for is still in the bloom of middle age. The best birthday gift you can give it is continued and careful maintenance.
What we would do to repair rotten windowsills and frames would depend on the extent of the damage. One thing we certainly would count on, though, is that a century-old home probably has rot and that a good deal of that rot probably is hidden from casual view.
There are a number of ways to repair dry rot, but concrete isn't one of them. The ways to fix a dry rot problem range from scraping off surface damage and treating it with a fungicide to replacing the window frame or sill.
Before you start thinking about repairing the damage, you should think about what caused the problem.
Dry rot is a misnomer. In reality, dry rot is a fungus that requires moisture to live. It is prevalent in wetter climates and is virtually nonexistent in dry zones.
It took a while for Kevin, who grew up and worked in the San Francisco Bay Area, to accept that the high-desert climate of his current home near Boise, Idaho, does not support dry rot. Not that he misses it.
So, before you begin repairs, try to find the source of the moisture that caused the damage. For windows, it may be something as simple as a failing paint job. On double-hung windows failing putty is often the culprit - especially at the joints at the bottom of the window. Once you think you've located the source of the water, make sure to eliminate it.
The first step in repairing dry rot is to determine the extent of the damage. This isn't always easy. Often the fungus will feed on the interior of the wood, leaving the surface appearance normal.
In advanced stages, the surface will appear as if it is collapsing - which it is. To find the extent of the damage, do what the termite guys do and use an ice pick to probe the wood. If the pick slides in easily you probably have damage. Continue probing until the wood is solid. That's where the damage ends.
Small areas of rot can be dug out and filled. Wood putty works for small areas. For larger areas, Bondo is a good alternative.
Before you fill the void, make sure to give the hole a good coat of oil-based primer to ensure that the filler stays in the hole. We've also found that brushing a chemical fungicide provides a little extra protection against the fungus. Apply this before you prime and let it dry. If you use it, make sure the area is well ventilated and that you wear a respirator and gloves.
If the rotten frame is so far gone that filling won't work, you'll have to replace it. Call a structural and pest repair (termite) company or two and ask for recommendations.
Window replacement is a job you can do yourself, but expect to spend some time learning how double-hungs are assembled. Fear not, though, the learning curve is not that steep.
One tip. If the windows are to be painted on the inside as well as out, prime them before they are glazed. If the maker won't do it, ask if you can prime them before glazing. This will require a couple of extra trips to the windowmaker but could add to the life of the window.
Your windowsills will probably require some carpentry. Whether you replace the damaged sills or patch them will depend on the extent of the damage. If you're lucky, the damage will not extend throughout the sill, and a patch will work.
To patch the sill, cut out the damaged portion with a handsaw, making sure to remove all the rotten wood. Try to give yourself as much surface area as possible to join the old sill to the patch.
Consider cutting a 45-degree miter in both the patch and the old wood to increase the surface area of the joint. Prime all surfaces except the areas where the joint is to be made. Glue and screw the patch to the old work, allow it to dry and then sand it smooth.
To replace the sill, remove it with a chisel and pry bar and try to make an exact duplicate. Nail it in place (nail holes are easier to fill then screw holes). Make sure you prime the replacement on all sides with a good oil-based primer.
Remember, the cause of dry rot is water. A good paint job coupled with good caulking and glazing will prevent it. Locate the source of the water infiltration, stop it and then repair.
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