Just completed my annual fall repair of exterior window side trim and sill rot.. I continually find a couple of windows with rot at the base of the trim where it meets the window sill. I have noticed that windows where this junction was caulked (by the exterior painting contractor about 7 years ago) are the one that are rotting but other windows where the caulking was weak or has “failed” are OK. So should this area be caulked? How about where the sidding meets up under the window sill? I will need to paint again soon and want to give some guidence to the painting contractor. My house (built 1988) has OSB sheathing and cedar clapboards. NO HOUSEWRAP or even tar paper around the windows for flashing, just z-strip over the window header trim. The only way to keep this house from turning to mush in my N.H. environment is to keep it caulked perfectly tight. That’s what I told the painting contractor, did he overdo it? Probably my fault for overemphasizing caulking to him but I have had my share of replacing siding and clapboards and was reacting to that. He used more tubes of the best caulk than he had ever experienced before. Oh, the siding paint is in great shape. Two coats of SW Woodscape solid color stain and a pro painter is worth every $$.
Ted
Replies
Remember that most caulks will not adhere well to raw wood -- you need to coat the wood edges with a good quality primer first.
And before caulking make sure that the head flashing is in good order -- if water gets behind the window at the head the caulk just holds it in.
Use a good quality caulk -- I'm partial to Dap's better siliconized latex. Avoid pure silicone and oil caulks.
Not your climate, but most of the caulk on this house is 20 years old and still in good shape.
ted
Unsealed cut ends of trim is susceptable to failure, due to it's ability to wick up moisture. Paint and stains that don't allow water in from the outside, will hold moisture from escaping. Old growth wood could fight it off for quite a long time, newer vintage wood-not so much.
Whether you should caulk or not is up to you and visual inspection.
I've followed a "good" paint job b/4 and repaired rot in areas you mention. Usually a result of a caulk repair at the problem vs. sealing out the source of water entry. The caulk didn't allow the wood to ever dry out. Trim to sill is often the location.
So are those PIA sprinkler systems, bathing the area daily. Plants grow with water, trim don't.