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I have a alder house (c. 1876) that has some dry rot in the floor joists. I was wondering if painting them would stop the rot or if it would have to be physically removed first. The basement has a stone foundation about 3 feet below grade, and then it looks like sand jutting into the basement about 2 feet and down about another 2.5 feet. This part has a skim coat of concrete or plaster over it. I have a dehumidifier in the basement and it takes about 3 weeks to fill it, and there is no visible water leakage. Any ideas?
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Painting definitely wouldn't stop the decay. To do that you'd have to treat the wood with a fungicide, and maybe then boiled linseed oil. If you're leaving the joists in place, don't just remove the rotted parts. Treat them to kill the fungus, then maybe use a penetrating epoxy on the decayed parts.
*Calvin, There are a few ideas on how to treat rot on this page from the Rot Doctor.The info may or may not be applicable, but hopefully the pages can increase your base of knowledge and possibly detail a solution.
*Calvin:With regard to wood decay -- a 10% loss in weight equates to a 90% loss in bending strength.No surface application on dry wood will adequately penetrate more than a few sixteenths at best except on end grain. It will not "repair" the wood and even with complete penetration will only retard future growth of fungi. I also don't think that epoxies are particularly good in replacing/repairing bending structural members as most expoxies have low shear values.I am amazed that Red alder will last that long. It is a wood that is definitely not decay resistant. It is also not generally regarded as a structural wood. And if it is red alder -- boy I cannot understand why alder -- with all the Doug fir available in the PNW (unless you're not in the PNW). Are you sure it's alder????It also may be an old problem from a leaky water or drain pipe, a leaking sink or WC, etc. Is the rot active -- for that the wood has to be wet (above 25% oven dry moisture content). Are you seeing fruiting bodies (mushrooms)???? Is the wood cracking (lots of finely structured cracks) and fissured or punky? Describe the appearance of the wood in the affected areas!!!You might take a test plug from the center of the joist in an affected area using a small hole saw (eg 3/4") to determine the depth and severity of the "decay" you are seeing. Molds and mildews look ugly but generally they don't significantly affect strength properties as they are generally a surface problem.Sounds to me that this requires a professional evaluation at some point. Maybe you can be lucky and cap the existing joists. Floor joists are structural members and weight bearing is their function.A wood technologist near Sublimity OR!
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I have a alder house (c. 1876) that has some dry rot in the floor joists. I was wondering if painting them would stop the rot or if it would have to be physically removed first. The basement has a stone foundation about 3 feet below grade, and then it looks like sand jutting into the basement about 2 feet and down about another 2.5 feet. This part has a skim coat of concrete or plaster over it. I have a dehumidifier in the basement and it takes about 3 weeks to fill it, and there is no visible water leakage. Any ideas?