Laminating layers of plywood together - how to avoid warping

[Chris Yarish]

I am making an inexpensive (and quick) kitchen table for friend - long story, divorce, no money, etc.

I'd like to make the table top out of cabinet-grade plywood (I have 3/4" and 3/8" on hand), bringing the total thickness to ~1 1/2", then edge band it with veneer tape.

I am concerned about gluing 2 pieces of 3/4" together out of fear that the new panel will warp.

What is my best approach? I see a few options, and would appreciate some feedback:

1. Glue 2 pieces of 3/4" together (Titebond III or standard yellow wood glue)
2. Glue a sandwich of 3/4" in the middle, 3/8" on top and bottom. (Titebond III or standard yellow wood glue)
3. Either of the top 2 options, but with contact cement (would like to avoid this, due to smell of glue)
4. Skip glue entirely and just screw up from the bottom.
5. Don't make the entire table 1 1/2" thick, just make a façade, making just the outer perimeter of the table 1 1/2" thick

I have a Mark VI vacuum pump and some gigantic bags...so, I have the ability to toss the whole thing into a bag if needed.

My main goal is to make something that won't warp due to the lamination of the 2 sheets of plywood.

Many thanks.

[Mel Fulks]

Useing cabinet grade plywood ,rather than construction stuff, I don't see any problem. Don't mix any water into the glue or use any glue requiring water mix. Put glue glue on all opposing surfaces, not a thick coat on one surface. The only caution beyond this is if the ply wood pieces have any slight bow ,glue them in opposing positions.

[Chris Yarish]

Useing cabinet grade plywood ,rather than construction stuff, I don't see any problem. Don't mix any water into the glue or use any glue requiring water mix. Put glue glue on all opposing surfaces, not a thick coat on one surface. The only caution beyond this is if the ply wood pieces have any slight bow ,glue them in opposing positions.

So, either option....the 3/4 on 3/4, or the 3/8 - 3/4 - 3/8 sandwich should be fine?

The issue then, in preventing warping, is the moisture from the glue?

[Chris Padilla]

What's the size of the table?

Generally speaking, a good grade of plywood ought to stay flat. Be fussy with the plywood you select. Boards screwed/glued under the plywood can help it stay flat provided THEY, too, are flat...but you said quick 'n cheap.

I'd just use TB-II or III and spread it around with a low-nap paint roller so you can get it on quickly and evenly. The key will be providing good even clamping pressure and that can be challenging with a largish surface area like a plywood table. You'll also want something nice and flat to build it upon or clamp it to. Lots of cauls and lots of clamps might be in order or a veneer press or vacuum bag. But you said quick 'n cheap so lots of screws might suffice.

I'd go with 3/4 on 3/4. I'm not sure I've ever seen flat/coplanar 3/8 plus screws don't have much to grab onto with 3/8 and can easily break through.

[Mel Fulks]

I think it is the only possible problem if the plywood is pretty flat to start with. You can tell pretty much what you are going to get just by clamping with no glue to find best flatness direction. Many have done successful similar projects using glue containing water, but I think it best to avoid water.

[Morey St. Denis]

My sense is that your main concern is with the introduction of additional moisture deep within core layers of your laminate and potential imbalance of stress that may result. Why not use an identical type of moisture-free glue that is used in the lamination of plywood? Plywood manufacture typically uses phenolic resins sprayed, then hot pressed, between every ply, strand or shaving of bulk wood material. While heat and pressure of the pressed lamination process chemically polymerize and cure these resins without use of moisture or other solvent evaporation, you could accomplish the same result with typical two part systems that undergo a mild exothermic reaction without the requirement of adding heat or patiently awaiting evaporation. Suggest you might consider a two part resorcinol resin glue such as DAP Weldwood Resorcinol glue or else a very slow cure two part epoxy. The former is sometimes also found as DAP Weldwood Marine Resorcinol glue because it happens to be inherently waterproof and weather resistant; well suited for marine fabrications. Weldwood comes as an A-B two-part system that you will mix, a liquid resin and a dry powder. In my experience, any odor of curing resin is very mild and should be of little concern with adequate ventilation. Any modest amount of urea formaldehydes you might be introducing by use of an added single membrane or two of this product appears inconsequential in comparison to the resin content already accompanying most any laminated plywood product.

[John Blazy]

Ive done this gazillions of times when I was in high end millwork / cabinetry / furniture. PL polyurethane construction adhesive was always used - no influence at all on warpage, which wouldn't happen regardless of the adhesive because of the ply stiffness anyway. build up strips on edges are easiest - no wasted plywood, just PL or titebond 2" wide strips around perimeter, hold with spring clamps or PVC pipe clamps.

[J.R. Rutter]

Agree on no water for best results. Over a large surface area, it is amazing how quickly the wet face will expand and warp the sheet. A friend of mine (Terry Cain for any old Badger Pond people) with a millwork business told me years ago that he just used a web of yellow glue broadcast over one sheet of the sandwich rather than going for full coverage. This kept the water absorption to a minimum and still gave plenty of strength to lock the panels together into one unit.

[glenn bradley]

I make one layer the final dimensions and laminate the next layer with a 1/2" or so of overhang (less if the size/weight allows me to handle it). Use a known flat reference surface and some weights. Trim flush with a router once the glue is set.

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[Chris Yarish]

Ive done this gazillions of times when I was in high end millwork / cabinetry / furniture. PL polyurethane construction adhesive was always used - no influence at all on warpage, which wouldn't happen regardless of the adhesive because of the ply stiffness anyway. build up strips on edges are easiest - no wasted plywood, just PL or titebond 2" wide strips around perimeter, hold with spring clamps or PVC pipe clamps.

PL huh? Seems thick...how would you spread it so as to mitigate any high points....other than clamping the snot out of it....

[Chris Yarish]

I make one layer the final dimensions and laminate the next layer with a 1/2" or so of overhang (less if the size/weight allows me to handle it). Use a known flat reference surface and some weights. Trim flush with a router once the glue is set.

Yes, the plan was to cut one to size, the other oversize, then flush trim upon drying. It'll have to go in a bag though, as I lack sufficient cauls, clamps and/or heavy objects.

[Chris Yarish]

Agree on no water for best results. Over a large surface area, it is amazing how quickly the wet face will expand and warp the sheet. A friend of mine (Terry Cain for any old Badger Pond people) with a millwork business told me years ago that he just used a web of yellow glue broadcast over one sheet of the sandwich rather than going for full coverage. This kept the water absorption to a minimum and still gave plenty of strength to lock the panels together into one unit.

I generally work with yellow glue, but, had warpage on a piece I did a few years ago. Mind you, it was 1/4" on 1/4"....so, that's where my original concern came from. As someone mentioned, the thickness of the material might have been the problem.

[Peter Kelly]

4. Skip glue entirely and just screw up from the bottom.

Solvent-based contact cement and a few screws with 2 solid pieces of 3/4" material. Any water-based adhesives introduced will almost certainly cause warping and construction adhesive is just too messy.

If you want the top to really stay flat forever, laminate both faces with horizontal-grade HPL.

[John Blazy]

"how would you spread it so as to mitigate any high points....other than clamping the snot out of it"

PL PUR is lower viscosity than most construction adhesives, and its long open time allows it to flow a bit. Since it is moisture cure, and does not skin over like liquid nails, it will bite as good as titebond, with a fair degree of soak-in, and with a few weights overnight, I have cut through panels and saw about 1/64" of gap. I run lines of the adhesive about 2" - 4" apart when full sheet laminating. Wayy plenty strong for this application. What strength do you really need? If you are edge banding the 1-1/2" thick panel with veneer or solid wood, what stresses are on the innerlayer? four globs of PL 1" in DIA across a 3' x 4' panel are literally plenty if edge gluing wood tying in both layers.

[Mike Jungers]

I'd either use PL or West epoxy, but then I'm a boat guy and I epoxy everything. Spread whatever you choose with a 1/8" v-notched trowel, $2.96 at Big Orange. Both methods eliminate the need for heavy duty clamping, just spread the goop out and weight with just enough shop junk to get a little squeeze out.

Mike