Darryl Keil Last Activity 2026-01-12 8:29 AM
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Roger Barga

Posts: 19

Joined: 2003-07-09
Location: Seattle, WA

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Subject : help with surface flaw problem...
Posted : 2003-09-08 1:29 PM
Post #30970
I could really use some advice on a problem I’m experiencing in veneering. I have checked books and online FAQs and haven’t seen this problem described before, so hopefully someone here can help me out…

I just completed a walnut burl panel and was frustrated to find what is best described as depressions in the surface of the panel when I removed it from the press. There were several of these depressions, each about the width of a pencil lead and ranging in length from a quarter of an inch to about two inches long. They are not wrinkles or tears, but rather a concave flaw in the surface. They resemble worm tracks running across the surface of the panel. Given that these tracks don’t follow the grain of the wood and the panel was a four way book match but the depressions don’t occur on the same spot throughout, I don’t believe it’s due to a flaw in the veneer skin. I’ve seen this before in one or two other practice panels I made using different veneers, but it was just one or two dimples which I attributed to flaws in the veneer or the substrate (they were just for practice so I didn’t worry too much about it).

Again, I am hoping someone on this forum has experienced this problem and can offer advice on how to prevent this. If not, I provided additional details below and welcome any educated guesses or advice.

- the veneer was raw (not paper backed)
- I used a vacuum press (vacupress 100)
- a quarter inch top caul was used (there was no debris
or glue on the caul)
- the adhesive I used was industrial cold press veneer
glue filled w/ ground pecan shells
- the glue was applied with a 3/16" spreader (I did NOT
use a roller to even it out)
- I allowed more than adequate press time (it ran overnight)
- the substrate was 5/8 inch MDF
- the depressions can’t be sanded out (I tried and sanded
completely through the veneer skin).
- there were no flaws on the backing veneer
- the flawed surface of the panel was on the top (face up)
of the caul/veneer/substrate/veneer/caul packet.

Thanks,
Roger



 
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Thomas Stender

Posts: 18

Joined: 2003-07-06
Location: NY

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Subject : RE: help with surface flaw problem...
Posted : 2003-09-08 9:06 PM
Post #30971 - In reply to #30970
Roger,
This is mysterious indeed. I have seen depressions caused by wrinkles in the plastic sheet I use between the veneer and the caul. Could that be it? You don't mention a release layer. If you sanded through the veneer surrounding the depressions, there had to have been something pushing against the veneer from the outside. A depression in the substrate wouldn't produce those worm tracks if the caul were flat. And I don't think the glue had anything to do with it because glue problems generally produce high spots. Furthermore, they would likely have affected the four parts of your match in a recognizable pattern.

Some questions: Did you use another layer of veneer between the MDF and the face veneer? If so, why? When you sanded through, was there a substantial glue layer around the indentations? Did you try to "pop" the indentations with water and a steam iron?

It's very suspicious that the depressions are so thin and so deep. I don't understand how they would get so deep without something pushing them in. That leads me to think that there was something between the veneer and the caul that wasn't smooth.

Do the lines look regular or familiar in any way? Elephant whiskers? Do you live near a zoo? Just kidding, of course. I'm very interested to hear any more information from you or others' theories.

Tom


 
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Roger Barga

Posts: 19

Joined: 2003-07-09
Location: Seattle, WA

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Subject : RE: help with surface flaw problem...
Posted : 2003-09-09 1:01 PM
Post #30972 - In reply to #30971
Hi Tom,

Yes, it is quite a mystery as to the best of my knowledge nothing came between the caul and the veneer that could indent the surface. I do use plastic sheeting, but wrap it around the cauls (the whole veneer pack) just to keep glue squeeze-out off the vacuum bag and platen. I question whether a quarter inch top caul is thick enough, but this doesn’t explain the irregular pattern in these lines (my wife’s first comment was that my panel resembled a cerebellum – not exactly the compliment I was hoping for).

To answer your questions, there was no other layer of veneer between the MDF and the face veneer. There was a substantial glue layer under the spot where I sanded through. As for "popping" the indentations, it looked hopeless so I didn’t try.

I received one suggestion/observation from the company that sold me the glue (an aliphatic resin). They noted that cold press glue does not cure inside the bag and that the panel should be removed from the press after one hour to cure (I left it the press over night). They also advised using a thin layer of glue. While I can’t understand how this would result in the irregular indentations, I can see this might cause some problems. So, baring any new information or advice, I’ll give this a try later this week to see if it helps. In the future I will use Unibond, but would like to use up this bottle of cold press glue for my practice panels.

Thanks for your input,
Roger



 
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Darryl Keil

Posts: 1456

Joined: 2003-05-22
Location: Maine

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Subject : RE: help with surface flaw problem...
Posted : 2003-09-10 9:42 AM
Post #30974 - In reply to #30972
Roger,

Like Thomas said, your problem does not have any clear cause as far as I can see. I had in fact asked Thomas to see what he thought. I will say, that leaving the panel in overnight is definately not a problem and not the cause. I and many other folks have been leaving panels in overnight for years.

One thing I was going to mention, was that if there was a defect in the veneer it would have shown up on only two of the four pieces of veneer, and those two would be on opposite corners from each other. On a four way match two pieces are "up", so to speak and two are down. This may not help but its something to look at.

If you try it again and it still happens you are welcome to send me the panel and I will look at it personally. You can send the existing panel if you want but with all the sanding you have done I doubt I could see the problem clear enough to assess it.

Sincerely
Darryl Keil


 
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Thomas Stender

Posts: 18

Joined: 2003-07-06
Location: NY

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Subject : RE: help with surface flaw problem...
Posted : 2003-09-10 11:23 PM
Post #30975 - In reply to #30974
Darryl and Roger,
Consider this: There was considerable glue beneath the defect area, and the surface looked like a cerebellum. What if certain linearly-shaped areas were slightly weak for whatever reason, and the amount of glue in one area kept the veneer floating, and the veneer soaked up moisture in that area and tried to expand? The caul pressure would keep it from popping up, but the liquid glue would allow the veneer to fold down somewhat to relieve the pressure of the expanding veneer.
That's my theory, and I'm sticking to it until you guys answer.
If plausible, it suggests a few things:
That the 1/8" caul is plenty (I've use it many times),
That there was probably too much glue.
That Roger has plenty of pressure in his bag.
What say you all?
Best,
Tom


 
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Roger Barga

Posts: 19

Joined: 2003-07-09
Location: Seattle, WA

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Subject : RE: help with surface flaw problem...
Posted : 2003-09-11 2:29 PM
Post #30978 - In reply to #30975
I believe Tom has hit on the correct explanation. I left out a couple bits of information in my original posting, which at the time didn’t seem relevant. I made this panel following Paul Schurch’s decorative veneering video (same procedure is also described in the July issue of FWW). The center section of the panel was the walnut burl that ended up with all the worm tracks (depressions), and this center field was framed by other sections of veneer. The walnut burl wasn’t dead flat, but I figured it would flatten out in the press. I believe the walnut expanded as it flattened and it didn’t have anywhere to go because of the surrounding sections of veneer (when dead flat this center section of walnut veneer may have been a fair bit larger than the hole I had cut for it and, as Tom noted, may have expanded more as it picked up moisture). As Tom described, the veneer found a way to relieve this pressure by buckling along weaker sections (fault lines), pushing the glue out of its way.

I learned a lot from this – thanks again for all your input/suggestions.

Regards,
Roger
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