What type of plywood should i use for my exterior layer?

[wtfemery]

Hey guys, newbie here. I’ve been working on my camper project on and off for some time now. I was going for a very lightweight 6x10 squaredrop shape by simply stick framing with 1x2’s and 2x2’s, cramming all the gaps with 1.5” foamboard, then simply PMF-ing the outside and carpeting the inside. Though now after almost finishing with the foamboard i’m realizing it would be hard to get the exterior finish anywhere near smooth without some sort of flat plywood sheathing first. Also, i think the extra rigidity wouldn’t hurt. So i want to cover the entire outside with some sort of thin plywood or similar before doing PMF all around. I’m not really relying on the plywood for structural support, and it should be protected from the elements by the PMF, so what would you guys recommend I use? i’m on a tight budget so the cheap Tri-PLY underlayment type paneling is calling to me but i’m not sure if that’s going to be a bad idea. Not sure where to get thin baltic birch around my area, and it looks expensive… Thanks in advance.

 

[linuxmanxxx]

If your going to all that trouble and expense just use frp glued to the foam and wood or just float it with something to make it flat then stick with canvas. That underlayment hates liquid and will start delam quick when the canvas is saturated. If you want looks pmf is hard to get looking good with framing under it.
Steve

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[Pmullen503]

Flat roof? Use a good exterior plywood. I'd pop for a sheet of marine plywood, but that's just me.

PMF, especially with latex paint allows water vapor to slowly pass through it. That's what makes a good paint for wooden houses. So you don't want water to pool on your roof for days at a time. It's fine on a vertical surface or the typical curved teardrop that sheds water. When parked, tilt the trailer up or down to shed water.

You can use oil based paint with PMF which is how it's done in a marine environment.

 

[Tony Latham]

1/4" underlayment plywood. It's cheaper than 1/4" AC but with far fewer voids. It will add a ton of strength to your structure.

Tony

 

[philpom]

1/4" BCX is what I used for the roof. B side up, it's pretty smooth and the C side isn't visible. I put PMF on it using 7lb duck canvas, TB II and ultra premium exterior latex - so far it's perfect.

Maybe not needed but the first 2 letters in plywood designations indicate the quality of the finish so a BC has one grade B side and one grade C side, grade A would be the best. X denotes that it is rated for exterior use like house sheathing or roof underlayment. For my walls I used an AA furniture grade hardwood ply since I wanted a smooth surface for the PMF and a beautiful wood grain visible on the inside.

 

[philpom]

1/4" BCX is what I used for the roof. B side up, it's pretty smooth and the C side isn't visible. I put PMF on it using 7lb duck canvas, TB II and ultra premium exterior latex - so far it's perfect.
Affordable Movers in Los Angeles affmov.com
Maybe not needed but the first 2 letters in plywood designations indicate the quality of the finish so a BC has one grade B side and one grade C side, grade A would be the best. X denotes that it is rated for exterior use like house sheathing or roof underlayment. For my walls I used an AA furniture grade hardwood ply since I wanted a smooth surface for the PMF and a beautiful wood grain visible on the inside.

Hey! I’ve used BCX plywood before for a few projects, and I’ve found it to be great for exterior use, especially with the X rating for weather resistance. It’s a solid choice for roofing, especially when paired with PMF, which adds a lot of durability. For the walls, if you’re looking for a smooth surface, I’d recommend going with AA-grade furniture plywood.

Good point on the the wood choice, I used furniture grade hardwood ply for my walls inside and out. Makes for a spectacular wood grain look inside and a very smooth outer wall. BCX was used for the top and bottom only.

 

[Paintsalot]

I’m using 1/4” ACX on my build. No pmf though- I plan to just paint with real linseed oil paint over primer. The 1/4 Acx -is heavier than I expected.

The cheapest and lightest plywood option would be 1/8” utility plywood from Home Depot. Not sure how it would do with pmf though. Might be ok- could run a test sheet. Definitely not exterior grade.

Probably too pricey but just fyi- Noah’s marine sells 3mm marine plywood online. $70/ sheet though. They can cut it down to keep shipping down.

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