Plywood questions

[nikwax]

I visited my local plywood dealer yesterday (appropriately named Mr. Plywood) and asked about which plywoods would be best for my trailer project. He recommended MDO plywood for the floor, as it is free of voids and flat, and 1/4" void-free luan for the exterior walls. I've poked around on boatbuilding sites (as we seem to be trying to accomplish the same thing: rigid, lightweight structures that are weather resistant) and both MDO and luan are recommended materials for boats. One builder who visited mills said that MDO is layed up as carefully or more than marine grade plywoods are.



Any comments/experiences with these materials in the trailer building realm? I've used both materials in other projects so I'm generally familiar with them.

[caseydog]

MDO is heavily used in the sign industry. It would make a good TD material, as far as wether risistance. I'm not sure about weight issues, or off-gassing of harmful chemicals.

I've designed some signs that were applied to MDO, and the stuff used on those signs was pre-primed, and rather heavy.

I think it is worth some more research.

[Alphacarina]

While the MDO is rated for exterior use, the luan is not

I've never seen luan 'recommended' for any marine (or even exterior) useage . . . . but I suppose that would vary with whoever is doing the 'recommending'

Don

[Miriam C.]

Just my opinion but you only need waterproof wood is you plan on not painting/varnishing. Or if you plan some leaks. If that is the case I would not use luan from HD.

[Jeeper92]

luan would be ok if you were going to epoxy it correct?

[nikwax]

my source has exterior grade lauan, not to be confused with "doorskin." Boatbuilders use BS1088 graded lauan.

[nikwax]

a couple of snippets from "The Plywood For Boatbuilding FAQ":

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MDO (medium density overlay) is excellent for boatbuilding. It is usually produced to state highway department specifications and is supposed to last in extreme weather conditions with no checking, with only paint for protection for as I remember fifteen years with no deterioration. It is usually pressed up with douglas fir cores and centers, with a thin face on either side of lauan then over that the MDO, which is a phenolic resin impregnated paper which is stippled to easily take and retain paint. The MDO is impossible to separate from the plywood and is the reason why highway signs last practically forever.


The reason for the lauan faces is to create a smooth surface which prevents the grain of the fir from telegraphing it's pattern through to the surface. The same system is used for laminating fine-expensive wood veneer faces like teak over fir plywood, but without the MDO.

The cost of MDO varies, but sometimes is pretty expensive. Years ago as a consultant working in the plywood industry, I watched a lot of plywood being laid up in the glue room, and in general MDO gets at least as much care as marine plywood, sometimes more and even better materials on occasion.



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I've used Far Eastern lauan play for all my boats. It's about $15 a sheet for 6mm, $30 for 12mm. It is stamped BS1088, but if you believe that . . .

Nevertheless, its only bad fault is thin outer veneers - you need to be careful not to sand through them. Voids are small and infrequent. I used this stuff for an Oughtred skiff 8 years ago, finishing it with three coats of WEST epoxy and 2-part linear polyurethane paint. It hasn't needed repainted since then (apart from dings) and looks good for another 8 years at least. BTW the boat is kept outside all year round.

I used it 5 years ago for a Payson Pirogue and used household paint on it. Again there are no signs of delamination although the paint is flaking a bit, and the (polyester resined) glass tapes are showing initial signs of coming off at the edges.

More recently I built my Chebacco 20 with this - loads of epoxy and glass ou the outside of the hull, and 3 coats of epoxy inside. there are no problems after one season.

Having said that, I've seen other lauan (or similar) ply (from South America) that I wouldn't touch with a bargepole - filler patches in the outer veneers and so on. I guess careful inspection should be your initial guide.


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[GPW]

What about the weight thing ??? MDO is HEAVY ...

[Jeeper92]

Where can i get exteriro grade luan? do they sell it at the box stores?
I like hte luan because its so freaking light

Im startign to think it doesnt matter what ya use on the outside if you are going to epoxy it

[critter]

Hey Guys,
When is somebody gonna do a tear outta a cardboard box covered with epoxie!Gotta happen sometime!

[caseydog]

Hey Guys,
When is somebody gonna do a tear outta a cardboard box covered with epoxie!Gotta happen sometime!

I want to make one with Coroplast (corugated plastic), which is the same thing as cardboard, but plastic intstead of paper.

That ought to be REALLY lightweight.

[Jeeper92]

I was thinking to keep the weight down
i would use 1/2 on hte floor and luan on the roof and side braced by 1x2s, the luan is ext grade , lowes jsut got a shipment in and all of the pieces are relatively straight. Im going to epoxy the side after its done

[steve wolverton]

I want to make one with Coroplast (corugated plastic), which is the same thing as cardboard, but plastic intstead of paper.

That ought to be REALLY lightweight.

You are kidding...right?

[Jeeper92]

Is that a puffin logo??????????

[nikwax]

What about the weight thing ??? MDO is HEAVY ...

is it? Is 1/2" MDO heavier than say 1/2" ACX or AA? I'll look into it.


This is MDO we're talking about, not MDF