Gluing plywood faces

[tim walker]

I am probably over killing this project, but I have a lot of plywood all 3-1/2” w x 12” to 72” L. There will be two pieces glued. Obviously clamped, but how to hold together initially? I was thinking pocket hole screws ( is there a need to clamp with this method) or Brad nails then clamp. Also would you cut to length now or wait until glue up is cured? TIA

[Matthew Curtis]

If you are face glueing to each other and If screws are not an issue, I have always glued and screwed. No need for clamps at that point.
I would cut day after glueing

[tim walker]

How far apart would you space the screws? Obviously vertically two screws but length wise? 12, 18, 24”? And the screws can be removed I assume if needed? All of this will not be seen

[Jamie Buxton]

Do you have a brad gun? If so, that has the speed advantage over screws. And since this stuff won't be seen, I'd leave the brads in the parts.

If you're just gluing the two pieces together with nothing to align them while you're nailing, the parts are to squooge around. I'd cut them a little big, glue them together, and cut to final size after the glue sets.

[Rich Engelhardt]

When I glued two 24X24 pieces of 3/4" plywood face to face, to make a nice thick top for my flip top cart, I used TBII and rolled it out with a throw away foam roller, tacked the two pieces together with a couple brads (so the two pieces wouldn't slip) & then parked my van on top of it overnight.

[Don Stephan]

Any interest in insuring the laminated plywood is flat? Even 3/4" plywood sometimes is not flat.

[tim walker]

These are being assembled in the form of a semi-torsion box, so yes flatness is desirable if it can be achieved.

[Bruce Wrenn]

Sounds like a job for a "custom built" vacuum bag to me. Make pieces slightly over sized (length) to allow for pinning together in waste area. Glue it, pin it, and slip it in the bag. Run a vacuum on it for 45 minutes then take it out. Time is based upon using TiteBond type I or II.

[tim walker]

Agreed, it’s on my wish list

[johnny means]

If you're not making structural glue lams, don't make the mistake of complete glue coverage. It only creates a lot of volume that can't be displaced by gluing or clamping. A bead around the perimeter and a few lines through the field will hold just fine and flatten out easily. If I'm avoiding the vacuum table, I'll usually screw down the middle then clamp around the edges

[Jim Becker]

I agree with Johnny. And if you are using PVA, a whole lot of glue in the middle of such a lamination has substantially longer cure times because of being "locked inside" without exposure to air for moisture to evaporate. Perimeter and spot glue across the surface works just as well and cures faster in my experience. Assembling on a known flat surface is important if you need the result to be flat, too...like the table saw. I use the bed of my CNC machine for that now.

[Rich Engelhardt]

And if you are using PVA, a whole lot of glue in the middle of such a lamination has substantially longer cure times because of being "locked inside" without exposure to air for moisture to evaporate. Don't you ever wonder how that glue manages to ever dry?
You'd think that the glue around the perimeter would form an impervious seal & there would be no way for the moisture to escape through the glue film on the plywood laminations,,,,yet,,,somehow it does.

One day I might just glue some pieces together and see just how long it takes for that little miracle to occur. (the glue in the center drying)

[Jim Becker]

It does dry, Rich...but I've found it takes far longer "out in the middle" of a large lamination than nearer the edges...found that out by accident, of course, when I removed cauls way too early! It's especially a problem with "less permeable" materials such as factory finish MDF.

[Jamie Buxton]

Don't you ever wonder how that glue manages to ever dry?
You'd think that the glue around the perimeter would form an impervious seal & there would be no way for the moisture to escape through the glue film on the plywood laminations,,,,yet,,,somehow it does.

One day I might just glue some pieces together and see just how long it takes for that little miracle to occur. (the glue in the center drying)

The water in PVA gets blotted up by the wood surrounding the glue line, at least in the short term.