Building a Dimensionally Stable Panel Using MDF and Plywood

Question

Can one laminate an MDF panel to plywood and still maintain dimensional stability?

I'm building a 4' x 2.5' desk primarily out of maple (I intend to use either cherry or walnut for trim) and for the top I'd like something thick and heavy. Veneer core plywood is an obvious candidate for the top but it will be neither thick nor heavy enough. My idea was to laminate the plywood to some MDF and then use hardwood for edge trim. My concern with this is that despite the stability of both the MDF and plywood, laminating them together will cause problems with warping.

An alternative would be to build a frame similar to that of a floating shelf and then attach the maple plywood to the top of the frame. I have no objections to this but it's significantly more work.

Answer 1

Can one laminate an MDF panel to plywood and still maintain dimensional stability?

I'm not sure why would you might have thought that combining two dimensionally stable products would somehow introduce an instability. If you think about plywood itself, this is layers of wood veneers that aren't dimensionally stable but when glued together you get something that is dimensionally stable*.

Veneer core plywood is an obvious candidate for the top but it will be neither thick nor heavy enough. My idea was to laminate the plywood to some MDF and then use hardwood for edge trim.

That's perfectly feasible and how many working surfaces are made up these days. My workbenches are all essentially made in this way, the ply hiding underneath MDF in my case, with wood strips all around to provide a durable edge.

You do have to be careful how you go about glueing the ply to the MDF in a lamination like this if you want a good bond, it's not quite as simple as it seems. If you'll be using PVA (white or yellow), or foaming polyurethane adhesive, you want to make sure there's quite a lot of pressure holding the layers together which can be difficult to arrange without recourse to temporarily tacking or screwing the boards together, something you may not be able to do here (depending on the thickness of the veneered ply).

So if you can't tack the boards together while the glue dries be sure to use enough clamps or very heavy weights to ensure you're firmly pressing the centre of the panel together (clamping the periphery is not sufficient on larger panels). See more in Gluing plywood together. Do also take note of the tip in the last paragraph.

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*Not entirely, but so much so that its movement can usually be ignored.

Answer 2

Are you going to be in an environment with large fluctuations of humidity and temperature, perhaps outside the range of comfortable human habitation?

This is just a gut feeling, based on secondary experiences over time, but the combination you're suggesting has quite a bit going for it. The plywood is, of course, a series of laminations of wood, with grain in various directions. Adding a piece of MDF to this merely provides another layer, grain-less that should not generate distortions in the overall piece. The glue used to bond the wood should be evenly distributed and clamped as per manufacturer's instructions. In so doing, you're providing for the uniform application of force over the entire piece.

If the assembly is going to have extremely high levels of humidity and temperature, followed by dryness and cooler temperatures, I doubt the plywood would hold up on its own, nor the MDF. Even joined, moisture would be your primary enemy.

Perhaps if this applies, a sealer on the completed project to keep moisture out, but I'm betting that moisture is not a factor in your application.

I believe you can accomplish your objective successfully.