Structural Adhesives

[TGS]

I know this probably isn't the right forum to ask such a question but with so many people from so many walks of life, I figure it can't hurt...

Does anyone know anything about buying/using structural adhesives? Some manufacturers produce an insulated "log" where they glue together 2x8's with an insulation core.  What kind of glue do they use for this? I have an idea and would like to do some experimenting & testing to see if it can get off the ground.  But, finding a structural adhesive is a core requisite. I would prefer an adhesive that didn't need to cure in the presence of heat. I saw an episode of How It's Made where they were laminating wooden arches with glue and pressure. Pretty much what i'm looking for, glue and pressure.

Thanks.

[thecfarm]

Only guessing but probably takes ALOT of pressure. I would suspect a machine that could put out that much pressure would cost 100-200K.

[scgargoyle]

We had an old boat builder in Ct that built a plywood skiff with no fastenings- just clamped it together until the glue dried. The glue bond will be stronger than the wood with most wood glues, and you don't need a huge amount of pressure. What I don't know is what happens when the outside of the 'log' is exposed to moisture, and the inside is quite dry. I like Weldwood powdered glue- cheap, strong, and waterproof once fully cured. I would just buy a bunch of cheap C-clamps and go to town.

Just curious- being made out of 2X8's with a foam core- How much insulation factor would you really get? I can't imagine it would make enough difference to be worth the trouble. That's a lot of 2X8's to transfer heat.

[Kevin]

I use a construction adhesive called PL Premium.
The wood will rip before the glue lets go.

http://www.loctiteproducts.com/construction-adhesives.shtml#pl-multi-purpose-products

[Holmes]

Just curious- being made out of 2X8's with a foam core- How much insulation factor would you really get? I can't imagine it would make enough difference to be worth the trouble. That's a lot of 2X8's to transfer heat.
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The 2x8 will have an r value of 6.4 the space with 4" icynene foam will have an r value of [3.5x4"]  14, plus wood [3"x.8] 2.4 = 16.4 total r value .Not even as good as a 2x4 frame with fiberglass insulation. Holmes

[Brucer]

Adhesives don't do very well as "structural" materials -- they're no good at filling gaps between structural elements. They work best with a very, very thin joint where they act as a bonding agent. Generally speaking, the thinner the joint the better.

Pressure is used with laminated elements so as to make the actual glue joint as thin as possible.

Early airplanes were made of clear spruce lumber that was glued into laminated elements using a very basic glue similar to the "white glue" used for cabinet work. People were alarmed when they discovered the hardened glue was water soluble. However, the planes didn't fall apart (at least from the glue weakening). Researchers later discovered that moisture would never penetrate far enough into a joint to weaken it.

[Bandmill Bandit]

PL Premium is a a top notch product and does a pretty darn good job of filling small gaps, besides gluing various construction materials together very well. It doesn't work to "stretch boards" as I have seen some try to use it for.

[scsmith42]

Resourcinal glue is an excellent waterproof adhesive for laminations, and it is reasonably priced.  It is still used in aircraft assembly to laminate wooden spars, wing components, etc., as well as for boat building.

It is a two part adhesive.

Here is a link to DAP's info on it:

http://www.dap.com/docs/tech/00030205.pdf

[TGS]

On the show I watched they used a series of allthread rods and torque wrenches to act as clamps. Come to think of it the show was on history channel talking about sawmills and wood products. The company was building laminated beams out of 2x4's. Basically I need an adhesive that could be used on structural members like those laminated arches.

Thanks!

[scsmith42]

On the show I watched they used a series of allthread rods and torque wrenches to act as clamps. Come to think of it the show was on history channel talking about sawmills and wood products. The company was building laminated beams out of 2x4's. Basically I need an adhesive that could be used on structural members like those laminated arches.

Thanks!

Resourcinal...

[TGS]

 Hey thanks for the info on resorcinol. It may be just the ticket for preliminary testing. My big fear is delamination but with this being a marine adhesive I shouldn't have that problem. Do you know what the open time is?

Thanks

[scsmith42]

Hey thanks for the info on resorcinol. It may be just the ticket for preliminary testing. My big fear is delamination but with this being a marine adhesive I shouldn't have that problem. Do you know what the open time is?

Thanks

The open time depends upon the temp.  4 hours at 70F, 45 minutes at 100F.

Re delamination, aircraft built back in the 1950's with resourcinal are still flying...