Looking for Plywood Expertise

[Toytaco2]

I've called several of the large building suppliers and "door & plywood" companies in the Oklahoma City area looking for "oversize" plywood with no luck whatsoever. I have found 5x5 Baltic Birch available which I could splice to get to the 5x9 demensions for the trailer I want to build. But no one is being very helpful in explaining grades/interior/exterior, etc. except to say that all they have is "interior grade" in 5x5 Baltic Birch. Perhaps the sales people themselves don't know either. So, I'm looking for a little help here.

The Generic Benroy plans call for Baltic Birch, 1/2 inch for the floor and 3/4 inch for the sides without any further clarification. I think I've also read of people using Luaun 1/8 in thick for the roof skin. Should this product be available in "exterior grade"? I think also, I may have read about people using "cabinet" grade in their TD's. Could someone come to the aid of the "plywood ignorant" and explain exactly what I should look for in exterior siding and roofing (luaun?) for the Generic Benroy. I haven't decided yet whether to use 3/4 inch siding or sandwich/insulation construction but I will be epoxy coating and painting the outside and using the roofing tar process on the bottom.

Thanks,

[Airspeed]

almost all plywood use the same glue, they are all water resistant, if you want water proof you need marine grade.
CDX is 5 ply, is the ugliest and usualy used for roof sheating or for shear panels, CCX is 5 ply, has one good side,has plugs and is usualy used for roof sheating where one side will be exposed such as under the eaves of a house, SHOP is down graded AC plywood,it has plugs but also has a damaged area but at least 70% useable. AC is usualy the highest grade "exterior" plywood used in construction, has fewer voids, has plugs,usualy has 7 plys.
Like I said, all these plywoods, interior and exterior and most others use the same glue unless it is specificly "Marine"plywood.
I used 3/4 AC for my floor and walls. I did insulate the walls later.
Aaron

[Ralf]

Here in WV at Lowe's they sell BC as the best exterior. They also sell Birch and Oak 3/4 but all are only in 4x8 sheets. Any ply will work if you are going to coat it with epoxy. The cheaper grades would probably be sheathed or painted, the oak or birch can be epoxied and left natural if you want a "Woody" look.

I bit the bullett and ordered 5x10 marine Okame plywood from Boulter plywood in Mass. Ships by truck so double pricey. I finished sides with 3-4 coats of epoxy. I will clear coat it with auto paint when finished.

If you are going to paint or skin you can always scarf 4x8 to the size you want. It is not that hard to scarf and glue with epoxy. Lots of different methods. I scarfed 4x8 to make 4x16 ( 4x15 feet 6 inches) for boatbuild. The scarf joint is stronger than the plywood. The builders manual available on this site has a good description with photos.

I think for teardrop construction a half lap joint glued with epoxy would be plenty strong enough. In fact, I half lapped 1/2 inch 4x8 birch ply to make 5x10 panel for my pattern. Clamps, a straight edge and router are all you need. With half lap you could even go for the woody look with 3/4 Birch 0r Oak ply. To go 5x10 you add 2 feet to front end and have seam fall over the door, hardly visable. You are adding 1 foot by 10 foot to the bottom. This can be masked with trim or make it part of the design by routing shallow grove at glue line and laminating contrasting wood. There is a Benroy on this site with good looking contrasting wood along bottom.

[Ralf]

Check out photos of AmyH on this site. She lapped 4x10 to make 5x10 masked with nice design.

[madjack]

....we use "cabinet grade" ply...the stuff we get, has a Baltic Birch veneer over a Poplar core...this stuff has no patches on the exterior and I have never seen a void of any kind on the inside of it...the 3/4" has 13 plys and the 1/2" has 11 plys(versus 7 and 5 on cheaper ply)...this is a VERY stable product...we use a router to cut a 1/4 slot and joined the pieces together with a spline cut out of 1/4" ply...this was to make the 4x9x3/4 wall panels...we joined 5x5x1/2 for the floor using bisquits...epoxy was used for the adhesive on both...
madjack

[Toytaco2]

Thanks for all the good information. Sorry to be dense here Madjack, but is the 1/4inch slot cut into the 3/4" end/edge of the 3/4 ply (making the spline a sort of "really long biscuit) and how deep is it?

And another question, if I use the sandwich type construction - 1/4" ply exterior, 3/4" framing/insulation, and 1/8" interior, would I still need to splice each layer of plywood with these joints or would the internal framing be sufficient to hold everything together assuming I will use the epoxy sealant, then epoxy filler and then epoxy paint to finish the trailer.

[madjack]

Tt, the slot is cut into the edge of the ply and is 1" deep...I cut a spline outta 1/4 ply that is 1-7/8th wide...if doing sandwich construction, a butt joint over a framing members is fine, especially if using epoxy......
madjack

[nikwax]

exterior glue is waterproof, not water resistant. Marine plywood is no different in this respect.

[GPW]

We agree whole -heartedly with MJ... You should use the best plywood you can find...Sure, it's more expensive ,but produces a far Superior product with much better appearance and longevity(Look how NICE his TDs are...) ...Actually it's alot easier to work with too... We got ,what we thought was a good plywood from the HD and it turned out to be a Chinese product that didn't quite have all the laminations lined up , some overlapping.... producing little ridges in the final product ... Aargh !!! More sanding /worrying...wasn't cheap either "We won't be fooled again "

Our TD is 12' long so we had to join ply for the sides ... Butt joints with overlapping ply "battens" each side ,glued and screwed... which later turned out to be a good place to attach awnings /showers/accessory hooks,etc....easy /STRONG!!!

For outdoor ply projects we always slobber a mixture of 75% solvent (min spirits) and 25% Polyurethane on all the parts ...several coats seals the entire structure and waterproofs all the parts very well...Really sinks in .. Been using this trick over 30 years now and have never had a ply delam' or rot from water intrusion...and it's cheap ... a little light sanding and it holds primer or varnish great ...makes for a nice smooth finish ...depending on the quality of the ply of course...

[Ralf]

Although you can use most any plywood, I agree there is nothing like using the best materials rather than "making do" with inferior materials. That's why bargain studs (2x4) are no bargain at all when you have to work around all the defects.

I went first class and ordered 5x10 Okame marine plywood from Boulter Plywood in Mass. Sure it cost to ship motor freight to W. Va. but it is quality. I bought 3/4, 1/4 and1/8. I am lamenting the fact that I DIDN'T ORDER ENOUGH 1/8. Order extra, there is little or no difference in the shipping charges.

Friday evening out of the blue, I got a call from Chris Boulter asking if the shipment arrived in good shape and if I was satisfied with the product. That is the kind of guy I want to do business with. The Fantastic vent guy that everone recomends on this site was the same way. He called to make sure I was ordering the right model. Same with the guy from RV Wholesale.