Recently on one of the Woodworking forums there was a discussion of plywood panels and how to glue them into a frame, whether to allow for wood movement or to just glue them to the entire frame. The consensus among the answers was to glue all the edges to the frame, wood movement be damned. I was left with the impression that all the respondents believed that modern engineered panel material was absolutely stable and permanent. This advise was given without knowing what the project even was or where it would live.
Well, there were three possible explanations.  I am a crazy old man who is just resistant of change.  They have really improved plywood and particle board.  There is a lot of bad information circulating on the net. I decided to try and find out which was true. My wife says that obviously option one is the answer, but I’m hoping she is wrong this time.
Next let me say that I became a serious wood worker in the sixties, during that period we had a longing for all things natural and back to the earth, so I have developed an inbred disdain for engineered material of any kind. I rarely use plywood 0r MDF and only when it’s necessary for historical accuracy or to make something that will be used up or thrown away. I was actually horrified when Popular Woodworking ran an article extolling the benefits of particle board as a substrate for marquetry. While the pieces displayed in the article were beautiful, six months in a damp basement or one moisture episode like a flood or a leak in the roof and they are gone. In my mind plywood and particle board have always been representative of the cheap throw away furniture you see in discount stores and not to be used in heirloom pieces.
There is a common misconception that ply wood, OSB and MDF are dimensionally staple when subjected to seasonal moisture changes, therefore it is not necessary to allow for wood movement when they are used. Even the Engineered Wood Association recommends allowing for movement. While these products are extremely stable they are not totally stable. They will expand, warp and they delaminate which is a whole new problem. Warping, delamination and edge swelling are the most common problems. They are very stable in dimension compared to solid lumber, however they deteriorate rapidly compared to solid lumber when subjected to moisture. When lumber expands it expands more across the grain than with the grain, when plywood and MDF expand or contract they does so evenly in both directions this can be an advantage in some applications. Admittedly this movement is small but it is still movement and will eventually lead to damage.
The above and the following pictures are of what’s left of the top half of a Hoosier cupboard that was left in a damp, dirt floored basement for a long period of time. It was built sometime between 1900 and 1930 from solid birch rails and styles with birch plywood panels. I know this is an extreme case however there is a lesson to learn from these photos. If you look closely you will see that all of the solid birch components while having some damage are actually saveable while none of the plywood is.
The next picture is of a plywood back splat from a chair made in the 1940’s. This chair was not stored in a damp area but was in use in a home all along. Here again you can see damage and separation not as severe but there just the same.
If you are thinking those are pictures of old ply wood that was made with inferior glue here is a piece of two year old AC subjected to one flood episode.
I may still be a crazy old man but I still believe if you want to build heirloom furniture that is going to last for generations you need to deal with wood movement and use real wood at least until they invent glue and a finish that is really water proof. As to the best substrate for marquetry it appears that in the short run MDF works but will it be here in a 100 years? I guess I’ll never know, but it scares me to think of it getting wet especially with the new ultra thin veneers. This year an awful lot of furniture in the massive flood zones across the country took a swim, if it’s made out of wood it can probably be fixed, if it’s made out of ply wood or MDF maybe not so much.