Darryl Keil Last Activity 2025-09-09 11:09 AM
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Kevin Jenness

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Joined: 2007-12-04

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Subject : madrone burl flattening/ gluing
Posted : 2010-08-02 10:11 AM
Post #36124
We are starting a project incorporating about 100 square feet of madrone burl with pear veneer. The burl in its raw state is somewhat ripply; it appears to me that it can be pressed without flattening, but it is brittle and wants to split when cut. We have some GF20 from veneer systems, and my shopmate flattened several pieces following the included instructions, which don't involve drying the veneer thoroughly- he brushed on the solution, hung the leaves up for a couple hours, then stored them between 3/4" melamine sheets prior to laying them up on mdf with Titebond cold press adhesive. One week later, we are seeing some checks opening up in a specific area of the leaves prior to finishing, perpendicular to what appears to be the run of the grain. After looking through the forum, it appears that the veneer should have been more thoroughly dried with sequential interleaving of newsprint over a couple of days, and perhaps we should have used a uf glue rather than pva. Am I on the right track? Would you recommend trying to press a leaf without flattening just to see what happens? Is 2-ply recommended for flat panels of burl? Is gator ply sufficient for a backer, or should we be using raw veneer? And finally, is burl likely to check over time no matter what, or can we minimize it by proper technique?


 
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Darryl Keil

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Location: Maine

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Subject : RE: madrone burl flattening/ gluing
Posted : 2010-08-02 1:52 PM
Post #36126 - In reply to #36124
Kevin,

I've been in disagreement with the non-drying aspect of using GF-20, for exactly the reason you described.

Think about it, veneer thats not fully dried is pressed in a semi swelled state. Eventually its going to dry completely, and of course shrink, hence the cracks/fissures you are seeing.

From my experience the veneer must be totally dry before pressing. This is why I say, six times between newspaper over two days.

If you can cut and tape up the veneer without it cracking then you dont havee to flatten. I usually find madrone to be reasonably flat but I cant speak for what you have.

I dont think you need to two ply madrone burl, at least I've never done it. I also think urea glue is the best bet for any burl.

Darryl Keil


 
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Kevin Jenness

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Subject : RE: madrone burl flattening/ gluing
Posted : 2010-08-02 11:15 PM
Post #36127 - In reply to #36126
Darryl, thanks for your response. We are going ahead with flattening the madrone that has to be seamed, with a two day drying period, and have a leaf in the press with unibond to see how it does without flattening. Do you recommend adding pva to the GF20, and if so why, and in what proportion? Lastly, do you think burls and crotches are bound to check and break loose in the long run, or can they be tamed with appropriate technique and adhesives?


 
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Darryl Keil

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Subject : RE: madrone burl flattening/ gluing
Posted : 2010-08-03 6:14 PM
Post #36128 - In reply to #36127
Kevin,

The glue is not a must but it helps to hold the veneer flatter after it dries out as well as sizing it so you dont get any bleed through. Mixing ratios goes like this. 3 parts water, 2 parts yellow glue, and 2 parts GF20(undiluted).

Burls and crotches can be problematic, especially crotches, but with a good rigid glue and some other sizing techniques after pressing even these veneers can be tamed.

Darryl Keil


 
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Kevin Jenness

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Subject : RE: madrone burl flattening/ gluing
Posted : 2010-08-05 1:51 AM
Post #36129 - In reply to #36128
I went ahead and processed 10 of 20 leaves of our madrone burl with GF20 with added yellow glue, applied with a foam brush and pressed under full vacuum pressure with interleaved nylon screening and kraft paper. The leaves were pretty well saturated. I did it in two sessions, 5 leaves at a time ( the leaves are about 20"x63". The first batch I wet the veneer, cut two sheets of paper off the roll, layered it up, probably close to an hour from beginning to getting the stack in the press. At the first paper change I had that sinking feeling, as the first three leaves had real wrinkling issues- the leaves had expanded more in some sections than others related to varying grain orientation, and when pressed there were actually some areas where the excess swelling relative to surrounding areas resulted in wrinkles overlapping. The two worst leaves I rewet the problem areas and continued on, with some 1/4" cauls in the stack between paper/screen/veneer sandwiches to ensure flatness between layers. After 4 paper changes the wrinkles are much reduced though still evident, the overlaps are gone, and it looks as though we will be able to press and sand the processed leaves ok. The second batch I precut the interleaved paper and got the resulting stack pressed much more quickly, with less alarming initial results, although there were still some spots with minor overlapping. I think in future I would apply less flattening solution via spraygun to avoid excessive swelling on this kind of irregular grained veneer, and be sure to get it pressed flat as soon as possible. Any comments?
I was interested to hear in our phone conservation that some troublesome veneers are processed with steam post slicing to enhance workability, and that perhaps this batch of veneer had not been treated so. Certainly the madrone burl we worked with a couple years ago did not have the brittleness of the current batch and did not require flattening. Can you tell me anything more about this steaming process and how common it is in the industry?
Thanks again for your expertise and hosting this forum. It is a great resource.

Kevin


 
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Darryl Keil

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Subject : RE: madrone burl flattening/ gluing
Posted : 2010-08-06 9:35 AM
Post #36130 - In reply to #36129
Kevin,

I dont know if you did this, but one thing I do to prevent wrinkling issues while flattening is to flip each veneer piece end over end and side over side so the waves you are trying to flatten dont all end up stacked in the same place, especially when you have a lot of sheets to flatten. Sometimes I'll also place a thicker caul, like 3/4", on top for a more ornery stack.

I dont know how exactly how they pre-flatten veneer with steam but a number of burls are done this way, walnut burl usually being one of them as well as madrone. When you order burls and crotches asked if they have been pre-flattened, most suppliers will know if they have been.

Darryl Keil


 
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Kevin Jenness

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Subject : RE: madrone burl flattening/ gluing
Posted : 2010-08-07 10:40 PM
Post #36131 - In reply to #36130
Yes, I did flip the leaves to cancel out ripple reproduction, put some extra 1/4" cauls in the stack and topped off with a 3/4" caul. After all was said and done, the first batch seems ok. The overlaps mostly disappeared as the leaves dried out (down to 12% as measured via pin meter- high ambient humidity seemed to preclude going much lower at the time) and despite some residual ripples, the first leaf pressed down flat but for one minor blip which should sand out.

I am processing 5 more leaves now. Initially I misted them heavily with a spray gun, but after one paper change there were still heavy ripples apparent in one area. I resprayed with a heavier coat, to my eye less than but close to what I put on with a foam brush, and after the first paper change the ripples were pretty much gone. Crossing my fingers now and hoping for success. It seems like flattening is a a touchy process, at least with with this particular batch of veneer- I have always been able to avoid the flattening process in the past. I think spraying makes it easier to modulate the coating thickness and get an even application. I would guess that burls are one of the more difficult types of veneer to process due to random grain direction. In the future I will experiment with one leaf of a shipment before committing to an unfamiliar process, and certainly try to establish whether a particular flitch has been steam flattened. Thanks again for your advice.

Kevin


 
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Darryl Keil

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Location: Maine

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Subject : RE: madrone burl flattening/ gluing
Posted : 2010-08-09 8:01 PM
Post #36138 - In reply to #36131
Kevin,

Your difficult with the flattening of the madrone burl is unusual. First because madrone is usually nice and flat, and second, because flattening is rarely as troublesome as it has been for you. I have flattened many different veneers over the years with no problems.It doesnt make sense but I have never had to flatten madrone. Rest assured if you do it again its very unlikely you will have so much difficulty.

Darryl Keil


 
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Kevin Jenness

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Joined: 2007-12-04

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Subject : RE: madrone burl flattening/ gluing
Posted : 2010-08-10 12:08 PM
Post #36142 - In reply to #36138
In the end all came out well, the residual ripples in the treated veneer pressed flat enough to be sanded. One note of interest, the last batch of leaves was sprayed with somewhat thinner coating than previous brush applied treatment, and when dry it was 1/2" smaller than the first batch (over 63". I can only guess that the extra glue and glycerin bulked up the cells more and the glue held it oversize.
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