Darryl Keil Last Activity 2025-09-09 11:09 AM
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Ken Irish

Posts: 5

Joined: 2013-04-26
Location: Duvall, WA

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Subject : Veneer bubbles 5 years later...help
Posted : 2013-04-26 7:09 PM
Post #36890
The photos show the concave side of a curved face (back) mdf audio speaker. I have pressed veneers with Unibond and the Vacupress for the last 15 years. This is the first job I have had come back to me. These speakers have been kept in a climate controlled room without excessive heat or sunlight. (I understand the room is filled with about 750K of audio equipment which makes me believe that excessive environmental variables are not the problem.) This condition occurs only on the concave face of both speakers. The convex faces, veneered at the same time, same glue, same species, same finish show no problems. Nor does a flat veneer job on a nearby woofer box. (veneer direct to mdf) I paper taped and pressed the Pau Ferro veneer to the brown paper backing by Neenah (http://www.neenah.com/technical/heirloomfurniturecomponents/veneerbacker.aspx)and then pressed the paper and veneer two ply to the mdf core in a separate pressing. It seems the only difference in application or materials or use and exposure to elements is the convex vs. concave variable. That seems to suggest either a difference in how I was able to get the bag to apply pressure to the face OR the nature of compressing the veneer along an interior curve vs. expanding the veneer over an exterior curve. We're going to tear this off and do it again and I'd like to make sure this is not going to be an every five year occurrence. I'd sure appreciate your communal wisdom. There is a good thread here https://www.vacupress.com/forum/thread-view.asp?threadid=17231&MessageID=36755#36755 but my situation changes due to the condition only occurring on the interior curved face which takes my thinking away from the topcoat finishing. (conversion varnish in this case. ) Thanks for your help.
Attached file : PauFerro 1.jpg (34KB - 127 downloads)
Attached file : PauFerro 2.jpg (37KB - 88 downloads)
Attached file : PauFerro 3.jpg (25KB - 70 downloads)



 
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Don Stephan

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Joined: 2003-07-18
Location: Cincinnati, Ohio

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Subject : RE: Veneer bubbles 5 years later...help
Posted : 2013-04-27 6:36 PM
Post #36891 - In reply to #36890
Can't tell from the pix the radius of the curve, nor the orientation of the cracks relative to the direction of curve.

Have you used this paper backer on other concave surfaces? The company website talks in terms of hot melt on the surface of the paper, which might have interfered with Unibond adhesion.

Did only one concave speaker surface fail? I'd expect speakers to be in pairs. Were the same materials used on other types of speakers in the job - i.e. is the problem just with one type of speaker (I don't remember the names of the different types).


 
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Ken Irish

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Joined: 2013-04-26
Location: Duvall, WA

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Subject : RE: Veneer bubbles 5 years later...help
Posted : 2013-04-28 12:05 PM
Post #36892 - In reply to #36891
Thanks for your response Don.
The two speaker panels are 17" wide by 65" tall, essentially a 5" thick curved panel on a 20" radius across the 17" width. The grain runs perpendicular to the curve. The condition only occurs on the interior radius face, though the same paper, glue and application process as well as exposure to light and heat are the same on all faces. This particular backing paper has been sold by our local supplier of Unibond and we have used it without incident with Unibond on a number of occasions. We have requested pictures with a larger field of view from the customer that may help us to better assess the issue. We veneered a flat, square speaker box in the same room which didn't require the paper backing. As far as we know it is not exhibiting this problem. We are told that the speakers' fronts(convex) and backs(concave) have the same exposure to temp/moisture though I will be asking for certain confirmation that there is not an air conditioning vent hiding behind each speaker....I'm grasping at straws!


 
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Darryl Keil

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Joined: 2003-05-22
Location: Maine

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Subject : RE: Veneer bubbles 5 years later...help
Posted : 2013-04-28 12:22 PM
Post #36893 - In reply to #36890
To me it looks like the adhesion problem is not between the paper backing and the substrate but rather between the veneer and the paper, at least thats what I see from the pictures. If it was between the paper and the substrate it most likely would not follow the grain structure of the veneer so clearly. Bonding issues on the concave surfaces, again would be between the paper and the substrate. The only thing the concave surface does to the veneer is give it a more compressive force that the convex surfaces.


 
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Ken Irish

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Joined: 2013-04-26
Location: Duvall, WA

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Subject : RE: Veneer bubbles 5 years later...help
Posted : 2013-04-28 1:46 PM
Post #36894 - In reply to #36893
Thanks for your input Darryl. Yes the movement all follows the grain structure which suggests that there probably is not a problem with the glue/paper bond because it appears good between the paper and the substrate. The movement looks like an older piece of furniture which has been exposed to moisture and temp fluctuations. We will be asking more questions about the room conditions.


 
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Ken Irish

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Joined: 2013-04-26
Location: Duvall, WA

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Subject : RE: Veneer bubbles 5 years later...help
Posted : 2013-05-06 12:52 PM
Post #36905 - In reply to #36893
Darryl,
A note from a participant on the Woodweb veneering site: Does this merit consideration?
"And what's between the paper and veneer appears to be a rigid glue line that was put into compression when the flat 2 ply lamination was applied to a concave shape. Plastic resin is great for bent laminations that you don't want to flex, its not a good choice for flat laminations that you plan on bending."


 
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Don Stephan

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Joined: 2003-07-18
Location: Cincinnati, Ohio

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Subject : RE: Veneer bubbles 5 years later...help
Posted : 2013-04-28 6:25 PM
Post #36895 - In reply to #36890
The defects almost look like the wood tried to expand and lifted. One thought is perhaps the two ply was made flat, then the two ply was forced into the curve. This could place the wood under slight compression, but the amount of compression wouldn't seem that much.

Are the defects on the back of the speakers? If so you might ask for pictures of the wall and floor behind the speakers, so you can see placement of any registers, windows, et cetera.

Am I understanding correctly that the curved section is just a narrow band in the overall height of the speaker back? If so I'd expect similar defect on the entire back and not just in this narrow band. However, if confined to a narrow band it suggests the curve is somehow correlating with the defects. Did I understand that the paper was used only on the concave curve and nowhere else on the speakers?


 
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Ken Irish

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Joined: 2013-04-26
Location: Duvall, WA

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Subject : RE: Veneer bubbles 5 years later...help
Posted : 2013-05-01 9:38 PM
Post #36900 - In reply to #36895
Hi Don,
The speakers are a 6" thick curved plane yielding a concave back (which exhibits the problems all over the back) and convex fronts which have the same veneer, applied to the same paper and same Unibond glue and show no problem. The defect looks like what can be caused by temp and RH fluctuations, so your suggestion to request photos of the surrounding wall and floor behind the speakers is a good one.
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