Sandwich wall construction... glue question

[TimC]

I have the general structure cut out and before I proceed I would like to know if it is OK to leave some of my structure unglued. The five main vertical 1x are polyurethane glued with biscuits in the joint. The rest I'm hoping to simplify the process by leaving them loose until I laminate the whole shebang. Do you see any problems with that idea?

[TimC]

The five verticals are... front and back, hinge (frame), latch side of door and partition between cabin and galley. You can barely make out the outside profile line in black.

[noseoil]

I would think it's better to have a glued joint at each one & some type of mechanical fastener as well. I just use dowels for my side panels with one 3/8" pin at each joint. That's not really a lot of strength & it needs careful handling until the 1st skin is glued in place. Once this is done, the joints are locked by the glue & skin. When the 2nd skin is installed, it can't move at all. If you can't use fasteners (dowels, biscuits, pocket screws) at least use some glue & a clamp to hold things in place until the skin goes on.

If you look at the picture below, the block the panel is resting on is under the joint. Since my side panels are about 9' long, I had to join another foot of material onto the 3/4" side panel to get the full length I needed on a 4' x 8' sheet of plywood. Once it was trimmed into the frame, the only fastening was the three dowel pins & glue at each of the three joints. Not much wood there to hold, but the skin was enough to stabilize this joint & make it work. It's plenty strong enough once the skin is on.

[tony.latham]

Steve Fredrick's Teardrop Shop Manual says you don't need to worry about these interior joints. As you are well aware, the exterior plywood (either 1/4" or 1/8") acts as a gusset (and makes for a strong joint). If you doubt it, glue up a couple of 3 x 3' sheets of 1/4" ply sandwiched over a T made from two unjoined 1 x 4" pine boards. You can't get it to fail if you've done your job with the gluing process.

In this interior piece, it's held together –for handling purposes– by bisquit joints, pocket screws and one scabbed on piece that was removed after the off-side ply was attached.





Tony

[TimC]

Thanks guys. I think I will go with a combination of each suggestion. Some of the inside sandwich planks are critical as far as location, so, I will join them prior to gluing on the skin. Some others are OK if they move a smidge, though I don't think they will.

Gluing on skin... I like working with Gorilla Glue, but, I don't like the extra cost (which I admit is minimal for the build as a whole). I do like how it doesn't need to "dry". Rather it is a chemical hardening like concrete. If I use Titebond II for skinning I am afraid the moisture of the glue during curing will effect the lauan (1/8"). What do you think? TBII or Gorilla?

[tony.latham]

TB2. I can't imagine it'd stain your luan but I use 1/4" plywood subfloor. TB2 is stronger than GG. You've got a narrow working window with TB2 so be organized and maybe have an extra set of hands.

[tony.latham]

TB2. I can't imagine it'd stain your luan but I use 1/4" plywood subfloor. TB2 is stronger than GG. You've got a narrow working window with TB2 so be organized and maybe have an extra set of hands.

Do a test piece if you are worried about staining the luan.

[kitecop]

I made my walls by cutting out the interior with 3/4" plywood and skinned both sides with 1/8" ply. I used loctite PL adhesive and would NOT use it again for that application. I ended up with gaps all along the edges because i could not put enough pressure on the entire wall panel to press the glue for an even dipursal. Id go for a thinner glue that wont create any resistance on the skin making positive contact with the wall itself. Basically, u need a lot more pressure in more areas to get good even distribution and squeeze out on a piece that large when u use a thicker glue. I would use TB2 if i could do it over. The PL is good for gluing in the roof supports and any other application that has slight gaps.

[TimC]

Kitecop, yes, I will indeed be using TBII. I started using Gorilla on my skeleton and after a mishap (stupidity really) I realized it has poor strength compared to TBII. It expands and fills gaps well, but...

So far my build is coming along well. I'm finally realizing I need to make this a long term (months rather than weeks) to get good results.