Thread: Laminating 2 types of plywood

I think the problem you will have with the 4mm ply is that it will be thin laminations to make up the 4mm unlike the 18mm stuff. So on the surface it will look great,but it won’t last long as a bench top. I used 25mm mdf (still not cheap) but it has a hard surface, is even and with a bit of poly on it will stand up better than the surface of the 4mm ply. You could also put a sheet of Masonite over the top and just put a couple of screws here and there to hold it down and replace it when the need arises. My bench is 4.8mx600mm so one sheet of MDF covered it, I don’t have anything over it and it’s pretty hardy. A hardwood front edge stops the side of the sheet getting marked too. I’m with you though, the yanks have a ready supply of cheap and good quality ply compared to us.

Don't do it, it WILL bend.

I'm with Cal, 25 or 32mm MDF with a few coats of clear on it (make sure you do both sides or it WILL bend). I think you'll find that the skin on MDF is harder-wearing than ply anyway

Why will it bend? Is it the moisture?

I have laminated ply ply before and it was fine but not big bits like that. Also I believe they were two the same thickness rather than a thin and a thick sheet.

I used OSB left over from flooring years ago and screwed on a sheet of m.d.f. over the top so I can replace it in the future. Solid and flat.

Thank you for the thoughts and warnings

I had thought of MDF, in fact, I had considered making the cabinet and drawers entirely using different thicknesses of MDF (see original video). Unlike the video I am planning on using Domino to join the panels.

I wasn't sure if MDF would be up to the task of making full cabinetry from? It certainly is cheap enough, to be sure, so would solve problems on that end of things!

I'm also now wondering if melamine might be an option - it'd give me some practice with the material before embarking on other projects around the house with it...

Originally Posted by Mnb

Why will it bend?

The different thicknesses will move at different rates.

Thanks Elan. Makes sense. How much and how does ply move? Sorry if that's a big question.


I take back the comment about my bench top too. Reading a discussion about bench top thickness I remembered that I found and used the metal frame for some shelves. A rectangle with lighter metal cross pieces. Steel and aluminium perhaps. I added wood underneath and attached to the frame so it was like a double layer ladder of wood and metal. Then I added diagonal braces too. The OSB and then mdf was on top of the whole lot. So yeah I suspect that contributed to the strength of the top.

Flat sheet Ply will sag as gravity pulls on those areas not supported. That’s why ply should always be stored flat and supported- just observe how plywood bows if laid vertically against a wall in short order it will form a bow.

Also to glue two sheets of plywood together you will need a vacuum press because you will never get clamps to reach all areas equally.

You would be far better off cutting the ply into XXmm strips then gluing the faces together- this will allow you to achieve any thickness you want. It will also be more resist to sagging. It is also an extremely hard wearing work surface. It’s much like an end grain chopping block.

You could use any B/B grade or B/C grade that will work fine, small voids can be filled with epoxy. Just use polyurethane to glue up the lamination a half a dozen at a time.

C2A46F81-790F-4994-8FE6-234159FB70D6.jpeg

Originally Posted by Mnb

Thanks Elan. Makes sense. How much and how does ply move? Sorry if that's a big question.

Because ply is just sheets of solid timber stuck together, it moves much like solid timber; having the layers at 90 degrees to each other helps keep it dimensionally stable in length and width, but it can still cup and twist. It can move even without anything stuck to it, certainly covering only one face will make it go.

How much is hard to say, it depends on a whole lot of things like sheet thickness, layer thickness, timber type and grade. Sometimes it'll be dead flat, sometimes a 10hp vacuum pump can't hold it flat (and you lose it halfway through a CNC program ). In my experience, hardwood ply tends to be flatter as does the more expensive stuff like Birch and Hoop Pine. Thicker sheets also seem much more likely to be flat, I've had some 6mm interior Hoop Pine that looked like a potato chip.

Originally Posted by elanjacobs

Don't do it, it WILL bend.

I'm with Cal, 25 or 32mm MDF with a few coats of clear on it (make sure you do both sides or it WILL bend). I think you'll find that the skin on MDF is harder-wearing than ply anyway

Many thanks for this advice - by "clear", I assume you mean a clear varnish? I.E. Clear Varnish | Oil-based Timber Varnish ?

Originally Posted by Midnight Man

Many thanks for this advice - by "clear", I assume you mean a clear varnish? I.E. Clear Varnish | Oil-based Timber Varnish ?

Yep.

Given that it's a worktop, floor polish might provide a tougher finish.

In the old days, ply used to be almost as flat as a billiard table. Why? Because the veneers were sliced or sawn. Today, most of our plywood is rotary peeled from the log. This is a much quicker and better yielding method, but warping is the price we pay for rotary peeling.

Try this, my dad moved to the country and built a 6mx6m shed, and I bought this stuff for the bench tops in his workshop. Its top quality, great smooth shiny surface, and nothing sticks to it. so you can glue up on it then just wipe off the runoff.

Plywood products – Structural Plywood – Form Plywood

solid as a rock. But ultimately, if your frame is sturdy enough 18mm will be sufficient. Or for the same price/a little less as the Birch ply why not use one of these, especially if looks are what your after

https://www.bunnings.com.au/interbui...panel_p8330032
https://www.bunnings.com.au/2200-x-6...panel_p8330041

Doing a lot of wood carving with gouges and mallet, I need a bench that's so heavy that it won't start walking. Got that.
I need a bench with a top that will not rebound to bounce tools about. Plywood is too elastic.
Entire 240 cm bench and legs are 40 x 150 mm. Lower shelf loaded with junk and 4l paint cans.

All the laboratory benches at work were double 18 mm MDF and skinned with chem-resistant Arborite.
The skin only comes in black. Hard to look at for years on end.

Have you considered using formply?
Refer to these links inter alia if not.
https://plyco.com.au/products/dexiform
Green jewel - Sanctuary Magazine
Even a slice a concreter has just flicked looks priceless compared to c/d structural ply bench I have downstairs. [Or was it just a recycled lift-van?]