Veneered MDF Table Top

A furnituremaker wrestles with the issues involved in veneering a 1-3/4" thick MDF table top. March 26, 2009

I am currently working on a 1 3/4" x 42" x 84" kitchen table to be veneered in Maccassar. I am looking for advice on core options and balancing the panel. I am planning on vacuum bagging with precat urea. I would like to veneer one side at a time due to the size and weight of the top with cauls. I have considered a honeycomb core but still fear flipping the assembly during glue up.

I would like to veneer one side then once set, remove the panel, veneer the other side and immediately put it back in the bag. Will this result in a balanced panel? I also have concerns with the medex (waterproof MDF) top sagging over time. The top will cantelver the base by 20" at either end.

If it makes any difference Iím planning on veneering the edges first. Edges are curved and beveled. I will use three layers on the edge and then veneer the top/ bottom. Lastly the veneer does not seem oily or resinous - should it be wiped with solvent before glue up anyway?

Forum Responses
(Veneer Forum)
From contributor V:
If you use the precat urea as an adhesive for all veneering on the top, edges and top and bottom, it won't make much of a difference what you use for core material. Although not completely waterproof, the urea glueline will provide more than enough water resistance for any interior application.

Pressing the top one side at a time can be tricky when using a hot press. The cooling of an un-veneered side can be at a much different rate than one that is. But, in a cold pressing application, such as a vacuum bag, should not be a major problem. The top could be removed and flipped in as little as four hours or less, depending on the ratio the glue was mixed at.

As far as balanced construction goes, proper would be a cheaper veneer with the same density, grain structure as the other side. So, as the Maccassar Ebony expands and contracts as all wood does, regardless of thickness, the underside does the same.

I have never had to wipe veneer before pressing, either with PVA, or urea, hot or cold. I spent the last 12 years working almost exclusively in veneering at a custom shop that has shipped all over the world. We pressed thousands of feet of both domestics and exotics. Most boardroom tables were pressed using Urea Formaldehyde onto 30mm particleboard. Most everything was pressed onto PB.

From the original questioner:

Thanks for the input. I will forget about the medex and go with regular or Ulralite MDF, 1" laminated to 3/4". Does the Ultralite have any drawbacks? I have and am planning to use anigre for the backer. I was also planning on using a heating blanket around the glue up to set the panel faster. I think the blanket doesnít heat over 100 degrees. Will avoiding any heat help produce a flatter product when veneering one side at a time?

From contributor J:
I'd press a core of two layers of 5/8" baltic birch, with 1/4" MDF on both faces. This gives a lighter core, that still has the flat, smoothness of the MDF. If you are cold pressing, pressing one side at a time shouldn't give you a problem with Unibond.

From contributor V:
I would avoid the heat blanket on this one. The only problem I have with MDF is the dust. PB will be lighter and will produce less fine dust. Baltic birch would give a "higher quality" product, but unless specified by the client, is an unnecessary expense.

From the original questioner:
Any advice on spreading the glue evenly? I was thinking pouring glueout with a 3/32 trowel right behind then a quick roller across surface. I donít do constant veneer work so I donít think I will be getting a glue spreader. I also donít see cleaning a glue spreader (with urea) being convenient.

From contributor U:
How you spread the glue is important and probably more important is the mil spread recommended by your adhesive manufacturer. One observation, most glue spreaders for urea and PVA (white) glues have grooved rollers. This lays the glue on in ribbons which are flattened when pressed to give a uniform glue coat. I don't know if there are any notched spreaders that do a small enough ribbon. The hand glue spreaders we sell put a dimpled glue pattern and clean up easily with warm water (even urea).

From contributor E:
I was in the business for nearly 40 years, and think the honeycomb core is a good idea as your table would then be less heavy (though still pretty hefty). I would glue up a poplar frame (3" wide, more or less), with a couple of cross pieces, fill the frame voids with the honeycomb, and use the 1/4 MDF or hardboard under the face and back. Then you could laminate the core, do whatever edge machining you like, and then the face and back.

Whatever species you use for the back should be as close to the face characteristics as possible (don't know what matches Maccassar, but doubt that anagre, which has only about half the density of Maccassar, would be all that good a match). A waste grade of the face veneer would be best if you have it.

From the original questioner:
I have already almost completed the top. It is solid MDF and as you can imagine, pretty heavy. I agree that the honeycomb would have been the best option although a little more work. I also agree that the anigre is not nearly as dense as the Maccasser. It was a choice made through inexperience, I hope I donít regret it. From what Iíve researched (not from experience) the backer veneer is to counteract the "pull" of the face veneer. The pull is created by the moisture from the glue leaving the veneer and the veneer shrinking after the bond. If Iím using Unibond I am not introducing any water into the veneer and after the glue line is cured and rigid the veneer shouldnít be expanding or contracting, especially after a finishing. With this logic I went ahead and have pressed the backer on. I will be pressing the face soon. Does anyone agree or will the difference in densities guarantee the panel to cup?

From contributor E:
As changes in humidity gradually change the moisture content of the veneers on the face and back of your table, it is possible (though by no means certain) that it will warp. The thickness of your top is on your side. Over the years, we made many, many tops with different species on the face and back (hot pressed) with few problems, though the veneer selection was far from random. It's my guess that you'll be ok as is, but it would have been a near certainty using a backer grade of Maccassar on the back.

From contributor E:
If at all possible, you should veneer both sides in the same day. Did you leave some glue out to check for curing? The first side does not have to be cured hard, but use cauls on both sides. I use 1/4" melamine.

From contributor J:
Wow! 1 3/4" solid MDF, that must be heavy. I hope your base is beefy enough to handle it and doesn't have huge overhangs because that thing will sag like crazy. The baltic/MDF core I suggested would have been stiffer and lighter and not as much work as the honeycomb for very little additional cost. You'd probably recover that cost too since it would be easier to move and you wouldn't need three gorillas to help you. But as contributor V says itís an unnecessary expense. You sure wouldnít want to give your customer a better product than they paid for.

Your backer should be fine. I have done many rosewood tops with mahogany or walnut backers with no problems. With Unibond we'd press the face at the end of the day, leave it in the press overnight, then flip and put the backer on first thing in the morning. I hope it turns out well.

From the original questioner:
Yeah its heavy but two can manage it fine. What makes you so sure it would sag? I voiced my concern about the sagging in my first post. No one else mentioned it in any responses. I can still take some preventative measures to keep it flat if i need to. What does anyone else think? The longest cantilever is about 21" and a span of 40". The top is two layers of 1/2 laminated to 3/4 with urea.

From contributor P:
I've been watching this thread with interest because I've been in the middle of a project where I'm veneering 2" thick by 10" deep shelves with Wenge over MDF. I chose the MDF over the other options simply because of its flatness. I considered honeycomb, torsion boxes, etc., but I had doubts about maintaining flatness across long spans (up to 13'). I went with 1" ultralite MDF doubled up, glued together with Unibond 800. No clamping at this stage, just screws, with the holes filled with Bondo. I tested it first. The glue joints were stronger than the MDF itself.

I vacuum bagged the veneer - just the tops and front edges. No bowing by the way, even after finishing. The longest shelf is 13 feet. This may be blasphemy, but I suspect there's a threshold where a balanced panel is unnecessary. My guess is it's when the substrate is around 1 1/2" thick. I have some potential issues with long spans, too, but I have some strategies to deal with them.