Sandwich wall 3/4 inch core material question?, OSB or ply??

[ajliquidation]

Just started the floor on my 4x8 generic benroy sitting on a HF trailer, next will be doing my walls. I like to buy stuff ahead of time so I don't feel the dent in my wallet all at once! I was looking at 3/4 ply wood and damn it's expensive!!! Seems like a waste of $52.00 a sheet because I'm going to cut it all to pieces. Does anybody here use USB instead? Or can some of the Experts on here tell me which direction is best or what to use? Thanks in advance Adam W. In KC

[Pmullen503]

Some OSB has a coating on it to make it somewhat waterproof. That may interfere with some types of glues. Best to test a small assembly to make sure it glues securely. Plywood will have better screw holding ability than OSB.

If you look at the total cost and the hours of work, it makes sense to use the best materials and pay a little more now. You won't miss the extra money years from now but may regret any shortcuts.

[backstrap bandit]

I prefer plywood osb when it gets wet it expands and crumbles plywood can delaminate however after building hundreds of houses I prefer plywood also I believe screws hold better in plywood

[tony.latham]

If you look at the total cost and the hours of work, it makes sense to use the best materials and pay a little more now. You won't miss the extra money years from now but may regret any shortcuts.

I'll give that statement a double bingo. (Use your imagination).

My experience with OSB (on a painted shed in a dry climate with an overhung roof) was horrible. I replaced it with the T-111 plywood that my house has on it. It's been there for twenty years. And no, I'm not suggesting you use T-111 but exterior plywood lasts longer than OSB. A lot longer. I also wouldn't suggest you use CDX plywood, because it has too many voids and seems frequently glue starved. I would think joinery with OSB would be problematic. Perhaps there's a way. Dunno.

Also, I don't think you could glue your exterior/interior sheathing using TB2 glue 'cause of the "glue" on the OSB (Is that stuff full of formaldehyde?)

3/4" AC plywood here, in the middle of Idaho and three hours from the nearest Home Depot, is $41. You might want to call around. When I build a teardrop, it costs me roughly $3500. Maybe more. Don't scrimp on your major items to save thirty or forty bucks.

Having said that... I've seen some builds on here that used OSB. I hope it works out in the long run. Most commercial camp trailers (the big-factory ones) use OSB in the floors and I think that's so they can get through the warranty period.

T

[ajliquidation]

Thanks everybody! Great point on cost and time! Tony please remind me what CDX is again, I have been out of the construction biz a while and have become rusty on my acronyms. Always enjoy your advice as I'm stealing your profile for mine!!!! Thanks again everybody, Adam W. In KC

[MtnDon]

OSB has its uses but a mobile trailer/RV of any kind is not one of them. Yes plywood costs more. If OSB was any good for a trailer all the cargo trailer manufacturers would be using it to save money. They use plywood on their walls. The good ones also use plywood flooring.

Many different grades are out there. The better softwood plywoods are A/C or B/C, one side better than the other. Not only do the C/D plywoods have the chance of more voids they frequently have fewer plies than the higher grades; another reason not to use them as that makes them weaker. FYI, hardwood plywoods are generally not made with waterproof glue.

CDX... the X means eXterior glue. CD is the grade, per side.

softwood plywood association

[grant whipp]

Something to consider when choosing "sandwich" plywood construction is what will the overall thickness be and can/will you find hinges and edge moldings to fit, or if you are willing to modify said moldings to fit your wall thickness. As an example, the aluminum Edge Moldings typically used to trim out the tops of your galley walls and around the door openings (assuming you will be building your own doors) is available in 1/8" increments from 1/2" up to 7/8", then takes a jump to 1-1/4" and again to 1-9/16". Keeping your door/wall thickness to 1" or less will allow the use of formed offset piano hinges for your doors.

In my typical sandwich construction, I start with a core of 1/2" plywood with 1/8" interior paneling ... the voids that I cut out of the core plywood I fill with 1/2" Tyvek-backed foamboard insulation ... than I cover that with 1/4" plywood sheathing, giving me a 7/8" overall thickness that my 7/8" Edge Moldings can easily cover, and I form my door hinges to that 7/8" thickness. There have been instances when I ended up with a 1" thick wall (typically when I use a 1/4" hardwood paneling for the interior finish), in which case I'll cut down the 1-1/4" Edge Molding.

Grist for the mill as they say ... ...! Good Luck on your build, and as always ...

CHEERS!

[tony.latham]

Adam:

I've given a bit of advice on this forum. I hope it's all been good and hasn't sent someone down a road that causes a night in bed head scratching and thinking. On a few of my posts, people have chimed in behind me and I've realized that they're right –more right than me. (or was I wrong?***)

But let me say this unequivocally; When Grant Whipp responds on a build question, listen. He's been doing this stuff for a long time and knows how it should be done.

Tony

*** I still think OSB sinks!

[ajliquidation]

Great advice everybody, much appreciated!!! Mr Grant I'm going with pre-manufactured doors and plan on buying my trim and moldings from you, great point on planing ahead for the moldings and trim, I hadn't thought that far ahead, always have to plan ahead on these things I'm learning! Guess I need to figure out my door thickness first then see what size trim and wall to go with. Thanks again everybody for the great advice!

[backstrap bandit]

By the way the grades of ply are CDX exterior grade AC interior sanded on both sides BC interior sanded on one side have fun and enjoy

[bobhenry]

Damn after 7 years I found out I did it wrong

[WillemII]

Hi, the main criteria I had when using plywood for my td was: is it waterproof? A canoebuilder that I know gave me a good tool: plywood that is sold as waterproof is always waterproof, and also much more expensive. He said a lot of non-waterproof plywood still is waterproof, but that mostly depends on the glue used during production. So how do you know if a piece of plywood is waterproof or not? Simply cut off a piece a few inches square, and put it in a pot with water and boil it (gently) for one hour. If it's still in one piece, it's pretty well waterproof. No use in using that plywood in your td if it has started delaminating.
I have 'boiled' samples of all my plywood used, and I'm pretty sure I've saved some bucks (euros) this way.

[ctstaas]

Hi All,
Here's a test I was lucky enough to perform personally. Is it harder to make a hole in plywood or OSB with my framing hammer? Plywood is much more resistant to puncture with my hammer than OSB. I would prefer to drive a screw into the side of ply over OSB. Some OSB I've used did not stand up to weather at all and plywood weathers very predictably. Plywood is long strands of wood laminated together, OSB is short strands of wood laminated together. Will OSB work Vs. plywood? invest in yourself and your Baby TD!
I used 3/4" CDX good one side for my floor, walls and partitions/galley shelves. I put the good side inside so I would not need paneling or veneer and if looks fine stained or painted.
Enjoy, Chris