laminating layers of plywood

[rfuerst911sc]

I have a situation where I am going to be laying up layers of plywood. There will be a base layer of 1/4 ", then a center layer made up of two layers of 1/2 " and finally a top layer of 1/4 " for a total thickness of 1 1/2 ". I want this to be as waterproof as possible, this is going into an RV and may be subject to roof/wall leaks in the future. So my plan is to apply many layers of varnish but here's the question. Is it better to glue this all wood to wood using wood glue OR varnish each layer and glue varnished surface to varnished surface with something like construction adhesive ? I'm probably over thinking this but I'm doing this restoration once ! Advice ?

[Rick V]

Stupid question but why not use two sheets of 3/4?
I would also not varnish then glue, just glue it together then varnish.

[Zeke]

You could use a light sealer on the wood, but not varnish. You can use contact cement to do this but you'll need a plan to put the pieces together with no air pockets. Other than screws, there aren't any clamps for this kind of work, only presses or vacuum bags. You can use some more traditional glue as well but you'll need a lot of weights.

Lastly, you need a dead flat surface to lay this up on and get good weight distribution.

[dad911]

More details... Curve, compound curve? etc. Got any pics?

[Zeke]

He won't get much of a compound curve out of plywood.

[rfuerst911sc]

In this situation I can't use 3/4 + 3/4. Milt I can't lay this up outside of the camper I have to do this in the camper. So it will not be perfectly flat. I'm relying on screws on part of the perimeter and piecing into existing plywood to build this up. It's difficult to put into words exactly what I'm doing. I think I will varnish just the exterior perimeter of each layer and be done with it.

[Hads930]

Do yourself a favor and look up West System epoxy. This stuff is what most if not all of the custom baotbuilders in NC use. I would put down the first pieces going north south, lay your next layer at a 45 across the grain of the first, screw down the layer with a **** load of screws, let dry and remove screws. Next layer 90 degrees to second, the top layer 45 to third layer. West sytem between all layers the i would skim the top of it to seal it all. A lot of work but the only way I would do it.

[sc_rufctr]

I'm currently making a sewing machine table and this is exactly what I did.
Overkill I know but I wanted a solid base that would dampen the vibration of the sewing head and motor.

I used two sheets of 18mm and one sheet of 10mm = 46mm total or 1.80 inch

Use Marine Ply and epoxy. No need to get fancy.

I used a foam roller and just painted it on. Then layered the sheets and placed concrete blocks on top to weight it down.
The first sheet was placed on my Starrett surface plate (granite) for flatness

[Zeke]

Epoxy would be perfect. West is 2wice the price of others. A plastics supply can send you a quart of A and B and you'll have some for other projects.

[rfuerst911sc]

There will be three edges that are straight and one end that will fit a radius. I think I now have a plan based on the replies here. My problem is I am laying up this plywood onto a thin aluminum skin so I have to support it from underneath. I will lay in the 1/4 " layer basically dry other than the outer edge which will be bedded in caulk. Then comes the first layer of 1/2 ". This will be glued to the 1/4 " layer and also be bedded in caulk on one long edge. Then the next layer of 1/2 " and finally the top 1/4 ". Once this is all glued together there are screws on the one outer edge from the bottom and the top that tie it all together into the aluminum stringers that make up the framework of the camper. This is very hard to describe but your replies are helpful. I will post pics in a few days of what the results are.

[RWebb]

those are nominal dimensions and won't be exactly as thick as you want

ok?

[TimT]

A little more info would help..

Is this a floor, ceiling, wall, or bulkhead?

How many S.F. will this laminate area be?

1-1/2" of built up plywood will be quite heavy, and depending on the application it may warrant using structural foam in lieu of a layer of plywood to save some weight..(With no loss in strength)

West System epoxies have a system that will work well, but there are other less spendy equals that will suffice.

[thumbdoctor]

There is pressure treated plywood available also.

[nota]

Originally Posted by thumbdoctor

There is pressure treated plywood available also.

fresh pressure treated will not glue worth a chit
and is mostly cdx aka crap/scrap void city
A-B with no voids aka marine ply
plus 1 on west system epoxy and get the pumps to mix correctly

[GWN7]

Pressure treated and aluminum do not mix. It will eat the aluminum.

Before gluing/epoxy lightly sand each piece.

[Evans, Marv]

When I made my work bench, I went to good ole H.D. and bought a 1 1/8 in. thick of T&G plywood used for sub flooring. That gave me a bench top of 3 ft. x 8 ft. with the left over as a back board for the bench. Unless you need more thickness for a dimension, I doubt you could laminate anything more substantial. If you needed the extra thickness, you would only have to glue on an extra sheet instead of gluing several together and worrying about it parting. I think the sheet I bought cost $35 at the time, so it will cost more now. Of course I paid $25 for a 4x8 sheet of crap plywood not too long ago that cost $17 a few weeks earlier, so laminating several sheets might end up costing more that a sheet of 1 1/8.

[Jim Bremner]

sounds like a TON of weight in a high spot.

[Bill Douglas]

Nice work SC.

[sc_rufctr]

Originally Posted by Bill Douglas

Nice work SC.

Thanks Mr Bill. I'm planning on starting my own thread soon but I may loose my man card as a consiquence.

[rfuerst911sc]

I am replacing the wings on a 1968 Avion C11 truck camper. The wings are the sections in the camper that are above the trucks wheelwells. They measure aprox. 22 " x 8 '. The factory did this with 1/4 " plywood on the bottom, then 1 " ridgid foam then a top layer of 1/4 " plywood. However this area is also where the truck campers lift system gets through bolted so in some areas the factory skipped the foam and went with additional wood. But their layup = 1 1/2 " thick. I am doing this on the passenger side of the camper which also has to carry the weight of LP bottles, the range/oven and the water heater. When I do this on the drivers side that area has to carry the weight of people sitting at the dinette table which also doubles as a convertible sleeping area. On the Avion truck camper forum I visit guys have done the same as the factory ( ply/foam/ply ) and others have done ply/ply/ply/ply like I am thinking of doing and both seem to work. The all ply will be heavier and that is a concern. I've also thought about using marine core type products not sure if that is lighter in weight ?