Laminating plywood for large table top

[Justin Freund]

I have a job coming up that requires a large (4’x9’) table top. The top will have a decal and epoxy so seams are not as important but dead flatness is. I don’t have a vacuum bag that big but I do have an assembly table that will accommodate.

I’ve never done anything longer than 8’ meaning I’ve always used 4x8 sheets. My practice previously has been to use MDF sheets as clamping weight. I lay the 3/4 cabinet grade plywood out, spread PL premium with a notched trowel (concerned about moisture and uneven setting of PVA causing warpage of the plywood). Then lay the next layer of 1/2 cabinet ply, and then 5 sheets of MDF. Wait overnight and repeat with another 3/4 cabinet ply. This makes a rock solid top that doesn’t deflect and allows the overhangs I need.

Since I now need a 9’ top and don’t have the ability to use longer sheets of plywood, my plan was to do the same process, but to stagger the seams between the top, middle, and bottom layers.

So just looking for feedback on my process. Anything anybody would do differently? Do I need to worry about Titebond II warping the layers? I’ve never used the cold press veneer glue. Would that be better? Should I use an MDF middle layer instead of all plywood? Plywood is obviously stronger than MDF but I’m not sure if it matters in a 2” lamination.

[Richard Coers]

By the time you did all that messing around with layers and seams, you could do a solid wood top and have a real quality product.
Second option would be to hire a cabinet shop to lay up the veneer top for you. Won't cost you any more, the client pays for the outside work.
Horrible idea to do a 2 stage layup. That's the easiest way to set up a moisture imbalance and get anything but a flat product.
The decal seems to be an odd request on a plywood table.

[Justin Freund]

Not sure how I’m not still turning out a quality product with plywood. I’ve done this many times before with dead flat results on a just a slightly smaller scale. As much as I would rather do a solid top, the money isn’t there for it, and definitely not for me to sub my part out. Also, they want the whole thing painted anyway.

[Tom Bender]

Hi Justin
You seem to be on the right track with your current process but I'd be afraid of that joint in the top surface. You might want to hunt up a larger sheet for just the top.

[Michelle Rich]

doesn't ply come in 4x10? special order?

[Robert Engel]

Yes I would check on oversized plywood too.

[Wayne Lomman]

Justin, staggering your butt joints does work. I have manufactured tops this way many times with success. The only change I would make to your process is to use epoxy to glue at least the top joint. If you use a single pack glue, the glue line will show. Epoxy won't. It will be stable and work well with the finish. The other thing you need to check is that the abutting pieces of ply are the same thickness. This is not a problem with good quality ply from the same batch but check with a vernier. It save a lot of grief after the event.

You could use MDF in the centre. Buy a 12' x 4' sheet and you don't have to butt joint it. This is optional though as it won't make much difference to the job. Do it whichever way seems to sit better in your own mind.

Richard, while a solid timber top is nice, this is a case of the end result dictating the materials and process. An epoxy top on solid timber can be too inflexible to accommodate seasonal movement and thus crack. Also the process of clamping is done in stages between stacks of MDF sheets which protect the job from moisture imbalance. Its a simple yet highly effective way to get the result. Cheers

[Carl Beckett]

Given you have done this same process, just with 1 foot shorter material, I would say this makes you the expert on how it works. Doing a known process but extending by a foot shouldnt be all that high risk if you stay close to your original method. Given you have good results with the method, I would be hesitant to start experimenting with different glues etc.

Staggering seams make sense - maybe not near the edges but maybe in thirds. I might tongue/groove the seams (could use a router). By doing so you essentially are making your own 9' plywood which should be close in strength to the plywood itself. Everything else follows your known method after that.

imo, solid wood is not 'always' a higher quality product. It depends on the design and purpose. Again since you have a method that yields good results you just repeat it but extend it out a foot - seems the safest to me.

[Jim Becker]

Plywood is available in lengths greater than 8' from real plywood suppliers. a 4'x10' would eliminate any seams.

[Tim Bueler]

Given you have done this same process, just with 1 foot shorter material, I would say this makes you the expert on how it works.

imo, solid wood is not 'always' a higher quality product. It depends on the design and purpose. Again since you have a method that yields good results you just repeat it but extend it out a foot - seems the safest to me.

I agree with these statements. I would add that even though your top is to have a decal there is a significant chance your top joint will telegraph, IMO. I made decorative panels for an elevator lobby that required 5' x 12' x 3/4" sheets of MDF so I know it's made. Perhaps you could top off your lamination with an oversize sheet of MDF. Even 1/4", if you're comfortable with your lamination methods, would prevent that top joint from telegraphing. Just a thought.

[Frank Pratt]

I just gotta say that 5 sheets of MDF is very little clamping force. That's about 475 lbs spread over 4608 sq. inches, which is just over 1.6 oz/sq. inch. A vacuum bag will do over 100 times that.

[andy bessette]

Get the longer sheets of plywood. Use epoxy glue. Don't Mickey Mouse it.

[Nick Lazz]

Cold veneer with vacuum press would be a good way to go. If you go that route use MDO as the base. Very stable and flat.