What’s the current thinkinkg concerning whether or not to caulk the joint where horizontal cedar clapboards butt to the vertical corner trim boards?
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Replies
As with many situations, it depends...
There is no hard rule on this.
Things to consider: Caulk is generally considered a secondary weather seal. I would not rely on it for bulk water manangment. Some folks use it for the condition you describe mainly for aesthetic reasons; similar to caulking siding butt joints. The success and longevity of caulk in these situation depends on how well the siding wood grain (mainly end grain) is sealed. If the wood grain works with substantial changes in moisture content where caulk has been used, then the caulk material will be subjected to high shear forces and usually fail rather quickly. After that happens, it's presence is a double edge sword. I say that because it can hold in just as much moisture as it can keep out. That said, some folks believe it helps keep some nesting insects out of siding and trim joints whether the caulks weather seal is compromised or not.
If the ends of the claps have been primed and painted you might get away with no caulk but I wouldn't bet on it. We bed the corners in polyurethane and then run a bead over the top of the painted clap.
WRCLA
I'd pay a visit to the Western Red Cedar Lumber Association's site, wrcla.org. They're the industry association that creates the installation standards. My memory is murky, but I am sure they required the end grain to be sealed, and I think that caulk or sealant was optional. Do pay attention to their nailing instructions.
curious
Andy why are you recommending he disregard the nailing recommendations?
Hey Mark, Andy said "Do pay
Hey Mark, Andy said "Do pay attention...."
it sure does
ill chock it up to my kids screaming extra loud that day...no wonder andy never responded.
HI Jimmien, If there is a gap, then caulk should be used. According to the building science folks, the ends of the clapboards should just touch the trim, and be left un-caulked (although throughly sealed end grain is critical). Houses with caulked joints tested "wetter" than houses left un-caulked. Also, caulk needs to be maintained. Spotty caulking is worse than no caulk when gaps allow water in. In this situation, uncaulked joints drain and dry quicker. I believe the best practice for new clapboard installation is to install them as the building scientists recommend - this has been my practice for years with no signs of issues.
finefinish do you seal the end grain as part of a back prime or pre-prime process when you do a siding job? If a GC uses a siding sub do they typically seal the end grain?
HI Jimmien, We always use primed red cedar clapboard, so backpriming is already done for us. We seal all cuts, notches, etc. with 2 coats of oil spray primer from a can or a quart cup and foam/chip brushes if wind blown overspray could end up on the wrong surface (the client's car for example). I do believe the siding sub is responsible for priming all cuts as he is the only one to have access to them. That being said I would make sure that is part of his and your understanding as some carpenters just refuse to paint anything regardless of what the right thing to do is.
Cedar claps-to caulk or not to caulk?
JIMMIE,
If the Corner Boards are not installed, cut a piece of 15# felt wide enough to extend beyond the C.B. by at least 3" on both sides.
wrap the felt around the corner and staple into place, then install C.B.'s
If they are already installed, cut a strip of 15# 4-5" wide and slip it under the C.B. at least an 1 1/2", then proceed with siding and
no caulking. All end joints should primed/ sealed with the appropriate sealer, i.e. same as the finish coating. you should have a
snug fit up against the C.B.'s(spring fit if possible). At butt joints(in the field) on a painted finish I have seen some guys use a
bead of caulk,but I prefer to use a slip of 15# felt 3" W x 5" H -(don't go below the bottom of the clap)- behind the butt joint. Use a
similar method on window/door installs, as the C.B.s, behind the trim, before they are installed.
just my 2cents
Geoff