plaster in seams between hardipanel??


The ceiling in my outdoor lanai in Florida is drywall with papered and compounded seams. The paper is coming up in places and there are signs this has been repaird in the past so I want to eliminate the problem. The ceiling is exposed to outdoor humidity, but completely protected from rain.
I've investigated various solutions, including vinyl beadboard sheets, wood planking (v-joint or beadboard), and hardipanel. By far the least expensive, is hardipanel, but the problem is how to handle the seams. An easy solution is to cover the seams with a batten and try to make it look decorative, but I'd prefer a completely flat ceiling as I have at present.
Hardie Products recommends caulking seams, but caulk shrinks, can't be sanded smooth, etc. So, my thought is to leave, say 1/8" (or less) crevices between panels and using plaster (no joint paper) to fill them, and sand it smooth. (Hardipanel is very little thermal expansion/contraction.) The Hardipanel comes in a smooth finish, but it's pre-primed, including the edges. My questions therefore are primarily as to whether the plaster would do the job.
1. Will the plaster adhere adequately to the pre-primed hardipanel?
2. If not, if I simply roughed the edges with a coarse file, would that solve it sufficiently?
3. If you think the plaster will work, and assuming it gets a good coat of paint, will there be any other long-term issues using plaster?
4. If, instead of intentionally leaving gaps into which plaster could fill (and hopefully adhere), I butt the seams and just use plaster to fill the fine remaining crack, does that make the solution better or worse?
5. Do you have any alternative solutions that will give me a ceiling that has very low long-term maintenance?
Many thanks in advance.
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Why not put up rock lath and hire a competent plasterer to do the ceiling? Use any good stucco product and it should last many years. You may even be able to get a pleasing texture finish out of the job. HTH
Joe
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One word: money. Thanks for the thought, though.
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Off the top of my head I'd do the seams with thinset.
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Interesting thought. But would thinset be able to be feathered and sanded to get a really smooth ceiling??
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wrote:

I do not think you can get invisible seams. Even if the hardipanel does not expand or contract any, what it is secured to does. I would give excellent odds that any non-flexible seam filler will crack. Plaster/stucco or drywall with taped seams are about the only choices for a continous smooth surface. I would seriously consider battens in a uniform pattern.
Don Young
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Dunno how it's holding up these days but back in the early-mid 90s I finished MR board under a banks' drive-up canopy on the cieling,the architect/specs called for EZsand 90 for every coat..We do'nt have as many days of high humidity here in the Midwest but there are some and a wide range of temps..Apparently the architect thought the EZsand would handle it after painting.. Joint compound will stick to *almost* any clean surface,,the enemies are oil,grease,greasy smoke and dust..Primer is an excellent bonding agent for joint compound of any kind..I recommend using drywall tape for added strength and 2 coats on that to feather it out,then 150grit sandpaper for a smoothe finish.. Dean
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Here are several ideas.
My dad is at Ocala with the same drywall soffit/ceilings on the covered patio and front porch. Yes, the tape came undone. I bought a bag of thermal setting compound and redid the joints. That was 10 years ago, still holding fine.
If you are going ahead with the Hardi, I would suggest H-mold or trim at the joints. I don't think you will ever get an even application of anything to hold on the joints. I have used the sheet Hardi material, though I usually use one of the textured panels. The caulked joints show. It is a great material with trim on the joints, perhaps one of the artificial trims like Azec. http://www.azek.com /
You might also price any of the plastic siding soffits. <http://www.royalbuildingproducts.com/products/siding/soffit/index.html
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BobAtVandy wrote:

We have similar ceilings in our condo atrium .. under roof but not enclosed. AFAIK, it is ordinary wallboard (old) with no taped seams. Seams are caulked but not filled up and the edge of the wallboard shows.
Our patio, with concrete balcony above, has 1x4 wood boards as the ceiling (painted). I would be concerned about bugs getting behind the panels if the seams and edges aren't filled. Ordinary wallboard should work fine if the seams and edges are sealed up well and all painted.
I don't know how Hardie compares to ordinary wallboard for shrinkage/expansion, but flexible caulk allows for it much better than a rigid compound. You can order the seams so that they are evenly placed and leave them visible, with just a little caulk to seal the seam but not fill it up.
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