Prepping for very belated Hardi finish
My shed’s been sitting basically finished for 18-24 months, awaiting my getting the rest of the house done and taking care of a few small details on it. And the stars are finally aligned to get it done. That and I want to get some more labor out of my nephew before he heads back to college in a couple of weeks.
It has Hardi siding that hasn’t been caulked/primed/painted beyond the factory prime. I know I’m going to need to scrub or pressure wash before priming and painting.
But I was wondering whether I need to try to clean up the joints before caulking. And does it matter between using something like PL poly caulk or some version of a latex exterior caulk? Haven’t used the poly caulk before, but the poly glues and foam have been very grabby regardless of the substrate.
Thanks!
Ted
Replies
Hardie used to recommend caulking butt-joints. Now they don't and my personal theory as to why is that Hardie maybe a very stable product and not expand or contract, the sheathing underneath (especially new construction that is still rather green) is not. This makes it virtually impossible to keep those butt-joints caulked. A reto-fit butt-joint flashing might prove to be rather difficult and time consuming.
I've found that the best sealant to use is an exterior polyurethane that is formulated for siding and trim. I can't think of a brand name, but you will find it at HD or Lowes for about six dollars a tube. It is worth every penny. If you are painting imediately after, you can get by with an exterior silicone/latex caulk, but you will have to check it more frequently then with the poly. Seeing how this is only a shed, I'm not sure how worried about it you are. I have used just about every brand and type out there, and polyurethane just simply works. It is rather messy and hard to tool. Get a thick pair of rubber gloves, neoprene or something I think, and have plenty of mineral spirits on hand to clean and smooth you joints. Good luck.
I like to use an aluminum slip sheet behind the butts. (A good use for trimmings & leftovers, IMHO.) I put a bend near the top to hook the top of the plank to keep it in place. I use PL poly caulk over that (primarily for looks since the slip sheet takes care of any moisture issues -- purely a personal preference) and I haven't noticed any issues with the joints opening up. You do need to let that stuff dry for an eternity before painting tho'. I usually give it a week or so.
Mike Hennessy
Pittsburgh, PA
Thanks. I definitely have butt joints to caulk, and they unfortunately weren't splined at all. Not a lot that I think I can do about that w/o taking it loose.
I'm more wondering about the gaps at cornerboards, door trim, etc. These tend to be 1/8" to 3/8", and I was worried about whether they might've gotten dirty enough to be a problem for caulk adhesion.
The shed is on piers and is about 18" off the ground on one side (it's on a hill). There's been enough rain splatter of dirt onto the first couple of boards there that it's going to take a good scrubbing to get loose.
Fortunately, paint prep is one of the few outdoor water uses allowed in GA these days.
3/8"!
Time for a new tape measure!
You should still be able to fit slipsheets of aluminum under the butts without taking the boards off. That said, brush the joints with a stiff-ish brush and you should be good to go with a good quality caulk.
Mike HennessyPittsburgh, PA