Hi folks,
Wondering if I can ask for your thoughts on the subject of caulking clapboards at the vertical joints where they meet the corner boards and window/door trim? Also, for caulking the scarf joints where clapboards meet.
I’ve seen recommendations for caulking the joint after the claps are installed and I have seen recommendations for ‘bedding’ the clapboard into a bead of caulk placed along the inside back corner of the trim. Finally, I have seen recommendations for no caulk at all. This latter method seems to make sense when you consider the many old buildings that were put up well before the array of caulking products now around.
The clapboards are quartersawn white pine and will be primed on all 6 sides.
My hesitation with caulking after the claps are on is that it involves a lot of painstaking work to make it look right and I can’t say that I’ve been all that impressed with the service life of a lot of caulking I’ve seen. Add to that, if it fails, it’ll likely hold a lot of water inside. It does however seen to be the most common approach taken these days…..not that that makes it best.
If I go with the ‘bedding’ approach, I’m guessing the intent is for the caulk to cover the endgrain of the clap and fill the gap so that water can’t move in. Also, minimises the caulk’s exposure to UV and cracking with a reasonably snug joint. Correct?
If I go caulkless, I’m wondering how tight the gap with the trim should be. If the gap is quite tight wouldn’t that tend to cause the water to ‘hang’ in the gap (surface tension)? A wider gap would encourage droplets to form and the water to shed.
Anyway, looking forward to your thoughts and suggestions.
Thanks!
Dave
Forgot to mention…
1) this is in Nova Scotia……very New Englandish climate. The building is quite exposed….lots of wind for drying.
2) the walls are constructed with a rainscreen (approx 1/2″ gap between claps and Typar wrap)
Replies
I'm a proponent of bedding the joints and seams in a bead of caulk. At the corner boards, I run a thin bead where the corner board meets the sheathing and also run a thin bead about an inch or so along the top of the lower clap. Need to use just enough to seal the joint but not so much that it squeezes out. Usually I use silicone (which is why I take care to avoid squeeze out) but have used latex on occasion. This effort takes a little bit of time but I simply include this in my cost estimates. Seems like with a properly detailed rainscreen you could probably omit and will be fine.
Here's what we're doing (6500 LF of CVG cedar clap installed) - ends fully bedded in Solar Seal #900 terpolymer sealant.
Now, the resulting end gaps at corner boards vary from 0" to maybe 3/32" (a few max.). No sealant will be used on tight joints. Starting with a joint that paint won't fill, we will fill those flush with paintable sealant - no sealant 'finger bead' on top of siding.
Jeff
I bed
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Also, for caulking the scarf joints where clapboards meet.
I put a small piece of paper behind the butt joints; it laps over the top of the previous course so that it acts as flashing.
Three things are certain in life; death, taxes and caulking will fail.
Inevitably where it fails, it allows water in but hasn't failed where water could drain. I've seen many older clapboard installations where butt joints were backed by flattened tin cans.
Pay attention to proper flashing details for a "mechanical" water diversion and forget the caulk.
Add to that, if it fails, it'll likely hold a lot of water inside.
Not if you follow the advice others have given concerning flashing. Put flashing (felt, metal, rubber, whatever) behind the butt joints. Place it so that it overlaps the next-lower course of siding.
Then be sure not to caulk or seal the bottom edges of the siding boards.
Politics is the antithesis of problem solving.
With a properly designed rainscreen? I wouldn't bother caulking at all. Rainscreen is designed to let air in all around for drying and pressure equalization. Let the system dry. Caulking will just trap water where you don't want it.
Flash behind board joints, though if you like...
Thanks to all for the suggestions. It's kind of reassuring to see the lack of support for caulking after the claps are on. It takes a real craftsman's technique to do that job well and as I mentioned, you still have to deal with failed caulk down the road. I did it on a previous building of mine and now I need to deal with some caulking touch ups (or try to remove it altogether).
I had been wondering how the end cut prime coat would hold up over time. Once the clap is on you can't access it again. Then again, it doesn't really get hit with UV and without anything to trap the water in the gap, it should dry pretty quickly. I guess those century old clapboards are still intact for a reason.......but it was a different class of wood back then too.
Really appreciate your help.
Dave
but it was a different class of wood back then too.
Good, clear wood was cheaper back then, but it's still available today. In my opinion, it's critical to buy the best quality you can find when it comes to siding.