So… I recently built a bookcase (walnut plywood construction) featuring four slab- style doors, about 21.5″ wide x 27″ tall. This was my first project with slab style doors –  my plan was to cut them from a sheet of 3/4″ Baltic Ply with a walnut veneer, apply edge banding, and call it a day. Unfortunately my sheets turned out to not be flat enough over the size I needed, and I was thus forced to call an audible a little later in the game than I would have liked…  

Since the bookcase paneling was matched to the door’s grain, I routed off the back 1/2″ of the door panels, leaving about 3/16″ thick worth of the original plywood with the matching grain on the front (I’d have liked to remove  more but didn’t want to risk accidentally puncturing the veneer). This I mounted to 1/2″ mdf (unprimed, adhered w/liquid nails) and then applied a walnut veneer to the back with contact cement. I installed the doors and after about a month or so, one of them has started to warp. (lower corner warping out, away from the cabinet, knob side) I’ve yet to go take a look in person, but figured i might as well prepare myself ahead of time with whatever insight is out there.

I’m guessing the warping must have to do with there being two different thicknesses/materials mounted on either side of the mdf panel? Should i have primed the MDF? or maybe these doors are just a little too big to expect to remain flat? I can only imagine that if one door has warped the others are soon to follow. Any thoughts on a solution? 

I’ve got another slab-style door project about to start, and they’re gaining popularity in my area so I’d like to develop a reliable but cost-effective method for their construction – I am a one-man custom carpentry/cabinet shop operation, and most of my projects involve 4-8 doors. 

Next time around I was planning to apply veneer to 3/4″ MDF, my reasoning being that MDF is more stable and less liable to warp than plywood. Now i’m wondering if perhaps it’s worth routing in a channel for some metal flat stock, like a 2.5″ wide  x 3/16″ thick strip a couple inches in from each edge (so as to not interfere with hinges/knobs). 

What do you guys think? How have others been building slab style cabinet doors?