MDF and Wood Veneer

Cabinetmaker using veneer over MDF wonders about balancing the veneer and using a "crossband" layer. He gets detailed advice from a full-time veneering professional. June 28, 2005

Question
I have done veneering in the past and I have done it mostly over a solid wood core using a poplar backer with grain perpendicular to the face. I now have an upscale kitchen to do in quartered sycamore, and I plan to use MDF as a core for the doors and drawer fronts. Im hoping the 50 plus doors I have to lay up will go much quicker with the MDF. I'm not a big fan of MDF, but have to say it is stable - provided no moisture is introduced.

I had planned to use a backer of poplar as usual, but the conventional wisdom seems to say that it's not necessary. I really want the best possible method that will withstand a kitchen environment. Also, some of these doors will be fairly large, 22" width X 42" height. Both sides will be done the same. I am wondering if anyone has any suggestions for what to do in this situation? Also, Im not sure if I should use medex or a similar H2O resistent mdf. Any help would be appreciated.

Forum Responses
(Veneer Forum)
From contributor J:
I'm wondering if you are using backer to mean cross-band - in my experience, backer usually refers to a balancing veneer applied to the opposite side of the substrate from the face. A cross-band is used between the substrate and the face veneer.

With that said, most people apply face veneers directly to MDF without using a cross-band. Make sure to use a balancing veneer on the opposite side of the MDF. Also, Medex, Medite, MR are all moisture-resistant MDF's and would be a good idea in a kitchen. Another option that I like for a stable panel is laminating two pieces of baltic birch - you can oppose any twists and come out with a nice flat panel that is more durable and holds fasteners better than MDF.



From the original questioner:
Yes, a cross-band is what I'm referring to. It just seems as though it would be a little more stable in that the perpendicular forces would cancel each other out, making it less likely to twist. Plus, the added thickness might not chip from an inadvertent knock from dishes, etc. I'm curios about the baltic birch ply. What thickness is used, and do you turn one of them 90 degrees when youre laminating?


From contributor J:

Any warp that's induced by the face veneer should be counteracted by the backer veneer, so a cross-band over MDF is really redundant. The best results come from using the same veneer on the back as on the face. Cross-bands are used in plywood and (less frequently) over solid wood cores to help control cross-grain movement - obviously not an issue over MDF.

In terms of resistance to a dish hit, your cross-band would have to be harder than MDF to make a difference. Also, some of the moisture-resistant MDFs are noticeably harder than a lot of the other MDFs. I think edges are most vulnerable, so if you're planning to self-edge with the sycamore, you might want to consider a hardwood lipping under the edge veneer. On a plywood-cored door this also helps prevent the plies from telegraphing through the edge veneer.

When I laminate up baltic birch, I keep the pieces parallel. I also try to oppose any twist in the two pieces, and in some cases I check the thickness with a micrometer and try to orient the components, so that variations from the thickness sander at the plant are cancelled. I've had better luck with stability, flatness, and rigidity with a 1" door than with 3/4", so that means two pieces of 1/2" BB, but of course you could do two pieces of 3/8" to get 3/4".



From the original questioner:
I have a question about possibly using hardwood lipping under the veneer as you mentioned. I assume you meant to add the edging first, and then lay veneer, rather than the typical way of an applied edge-band after the lay-up?

I have considered this, as it would look best in my situation. I'm just a little concerned about the edge of the face veneer getting chipped, whereas with a 1/8 to 1/4" edge-band it would leave a ding, but no chip. Also, without the cross-band, would the movement of the lipping telegraph through?



From contributor J:
If you keep the lipping narrow (1/8" - 1/4") and your trimming/sanding really flat, you probably won't see any telegraphing. Most high-end veneer work is lipped and/or edged before the face veneers go on. It's really less likely to chip this way than edging after veneering, and it generally looks better too. Give it a good edge break - an art/science in itself.


From the original questioner:
I pulled out the first pressings after using moisture resistant MDF without 2 ply, and the 1/4" lipping shows right through the veneer plain as day. The MDF is darker - almost brown, and the light sycamore lipping shows up lighter. It's more noticeable on the back where I used plain sliced instead of quartered, which is cut slightly thicker. Guess I'll use a poplar /sycamore 2 ply on the rest.


From contributor J:
Before you do everything with a cross-band, I would check a few things out. First, can you actually see through the veneer before it is pressed onto a substrate? In other words, if you lay it dry onto your edged cores, do you see this color difference that you are describing? If not, I suspect that what you are seeing in your pressed panels is not actually the colors of the substrate vs. lipping.

Second, what happens when you sand the panel? I am wondering whether you are actually seeing adhesive bleed or discoloration. You might be getting different bleed over the MDF vs. the lipping due to different porosities.



From the original questioner:
Yes, I can see the difference by laying the veneer over the panel prior to glue up. It's far more apparent with the backing veneer. I wish I'd of noticed that before I laid up the first batch. The front veneer is .025", while the back is .020". The glue is unibond 800 with white catalist. The glue thickness is unknown, however judging by the amount I've used, it is right at the recommended spread rate of 1 cup= 15 sq' . I applied it using a foam paint roller. Sanding has no effect on the panels.


From contributor J:
It sounds like you've pretty much identified the problem as see-through veneer. I've never encountered that problem in long-wood veneers, but there's always a first.