Best Way to Join Exterior Trim Boards
I guess the answer might depend on the material, and specifically for me we’re talking finger jointed cedar trim, as well as HardieTrim.
What’s the best and also most efficient (fastest and easiest) way to join exterior trim boards in a long run requiring more than one trim boards (fascia, water table, belly, etc.)? I’ve read a lot of people online, some butting them together dry, some caulked or glued. Some join with a scarfed 22.5°, 30° or 45° cut glued or sealed with caulk. Some maintain a gap and caulk, some caulk and squeeze etc etc… lots of opinions out there but GBA community has great insight so I came here for help
The way that sticks out to me as easiest and best is to glue a 30° cut joint together, while joining them w/ a common backing nailer. This makes a lot of sense and seems easiest to me. Thoughts? Your preferred method?
thanks for the help.
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Replies
Pockets screws on the back of the wood trims or use some biscuits if the board is not thick enough. Fast and precise. Make sure to use a waterproof glue like Titebond 3 and Blue-Kote or stainless steel pocket screws.
No idea when it comes to HardieTrim.
This seems actually pretty difficult. Either you prefab your 40’ long run and have four helpers, or pocket screw the backside of each joint that is already up against a house(?). The only place this seems possible is on the fascia and rake boards where the backside is accessible depending on the width. Sometimes they aren’t floating either because of a sub fascia. Am I missing something?
For long runs, you can prefab smaller sections with pockets screws and join them in place with a biscuit (or a scarf/butt joint if you don't have a biscuit joiner). Another way that might work is to nail only the top of your trim then join it to the next board while the back side is still accessible then finish nailing it to the house. Or skip the screws and join everything with biscuits. It's really depend how flexible and long your boards are.
Scarf joints work too but they are harder to make nice in my opinion. You also have to make sure that the joint is properly oriented to not create a reverse lap (less important if you are gluing the joint with waterproof glue).
I prefer to use pocket screws when possible because you don't need to wait for the glue to dry but sometimes biscuits are the better choice.
Anyway, when it comes to trim, in my opinion, it's always better to prefab as much as possible because walls are rarely perfectly flat but sometimes it's not possible.
Hardie is very specific re: their warranty. I'd give them a call.