Reply by Neophyte

Unibond 800 is good
Dap Weldwood is Ok

But just to put my 2 cents in, Titebond II is all you need. (Apply it with a roller.)

No matter what you use, it will need to be clamped to a flat surface in order to be flat.

How did you clamp the first one you made that warped?

- jbay

There were two pieces roughly 4’ x 2’, one 3/4” thick and the other 1/2”. Used regular wood glue, clamped the margins all around and used screws for the center. Trimmed to size on table saw, got two table tops.

You also gave a very thoughtful answer to my original question in a different forum. In addition to the problems identified so far (unequal plywood thickness, perhaps excessive glue) I want to add that I did not use a flat surface for reference as the glue dried. I had them dry on top of some 2×4 to allow room for the clamps. I also wonder if the pieces need to be smaller when glued as evidently with the 4’ x 2’ pieces there is a large center area that is only “clamped” by screws
Thanks
Marc

-- Marc, NY