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Walnut Veneer Blisters

2/13/19       
NMPatriot Member

Website: http://www.wwbydesign.com/index.php

It seems that almost everytime I lay down walnut veneer with hot hide glue it begins to blister before I finish with the veneer hammer. My HHG is applied at 150ºF and I heat my substrate before I begin. Oddly, not all the walnut veneer that I have used blisters. The redwood veneer backer that I use never exhibits this blistering behavior.

I have never coated the substrate with the HHG before I begin, but am wondering if this may be my problem. I think that the time to coat the substrate and then both sides of the veneer could be sufficient to allow the HHG to begin to gel which is why I have never done this.

As I write I'm wondering if the dinky round "hide glue brush" is slowing me down as well. I have read that a brush with a metal ferrule adversely affects the HHG so I have only used the small round brushes with non-metal ferrules for my work. Argh!!

My process: I coat the underside of the veneer with HHG, flip it over, coat the show side and then work the veneer hammer from the center out. To be clear - when I say "coat" I mean that the HHG is applied very liberally. If I were starving the underside of HHG I could understand the blisters, but that is not the case.

If anyone has any suggestions I'm all ears.

Thanks!

2/14/19       #2: Walnut Veneer Blisters ...
NMPatriot Member

Update!
After I removed the veneered substrate from my press the blisters were still somewhat visible. I decided to try and iron out the blisters or at least reduce them in height.

Process: I sprayed a test area lightly with water and then wiped it across the veneer with my hand. With the iron set to "Wool", I laided down a sheet of parchment paper and began ironing the dampened veneer. Not having any idea of how long was sufficient to heat up the hide glue and compress the blisters, I counted to ten (10) and hoped for the best while keeping the iron in constant motion. I then used my veneer hammer to flatten the blisters. I had to repeat this process twice, but the blisters were reduced significantly in height.

Many of these "blisters" were about an inch in length and about 3/16-inch in width. These may have been due to the figure in the walnut or how it was sliced from the burl. I have no idea.

After I was done with the ironing I placed the board back into my press for about four (4) hours or so. When removed the blisters were not so pronounced as they had originally been.

These cause a lot of extra work, so I hope to prevent these in the future by implementing these changes:
1 Using a quartz-halogen lamp to keep the immediate work area warm;
2 Using a wider brush to spread the hot hide glue (HHG) faster;
3 Coating the substrate with HHG and then both sides of the veneer.

Hopefully, these changes with prevent these blisters in the future.

Thanks!

2/15/19       #3: Walnut Veneer Blisters ...
Tom Gardiner

I am surprised that you are using a press after the hide glue hammer application. I have no experience in HHG other than reading several veneer books.
I have had similar problems pressing walnut burl with PVA in a vacuum press. The European veneer was quite thick and the undulations were huge. I tried flattening with glycerin solution which was partially effective. When I pressed I misted the face of the veneer with water before applying to the heavily glued substrate. My error was to pull them out of the press too early. I doubled my press time to an hour or so. I am not a patient man when veneering. I paid for it. I have found I can press down blisters if I catch them immediately out of the press. I use the same method, a moderately hot iron and veneer hammer with no extra glue application. This is type 2 PVA I am using.

2/15/19       #4: Walnut Veneer Blisters ...
John Van Brussel

Website: http://www.veneersystems.com

I strongly recommend using powdered plastic UF resin for Burls as they have crazy grain and lots of tension. The UF dries hard and is thermoset so the veneer will not be able to move. It needs 4-6 hours at 70F to cure properly in a cold press or vacuum press. Some people say this is too long but sounds like you have spent to close to that amount of time or more and still don't have 100% bond.

Urea - Plastic Powder Resin

2/15/19       #5: Walnut Veneer Blisters ...
NMPatriot Member

@Tom Gardiner

Thank you very much for your posted comments.

Your comment about my use of a press after using the veneer hammer gave me pause. I gave that some thought and concluded that years back I must have decided that press usage was good "insurance" against the possibility of the veneer lifting away from the substrate.

I also referred to back to my hide glue bible - Stephen Shepherd's "Hide Glue Historical & Practical Applications" book. I did not reread the entire book, but my quick perusal found no specific mention of press usage after the veneer has been hammered in place.

That said, my method has worked well for me over the years, but on the other hand, if the piece had not been in the press I would have seen the blisters early on and could have taken steps to rectify the problem while the veneer was still damp. Whether this would have made any difference I am not certain.

I leave a veneered piece in the press overnight. My press is nothing more than two large sheets of 3/4-inch melamine with a sheet of anti-fatigue floor matting. The show side faces the melamine. My clamps are about 50-lbs of weights.

Thanks again for your help,
Phillip

2/15/19       #6: Walnut Veneer Blisters ...
NMPatriot Member

@John Van Brussel

Thank you for taking time to lend a hand.

I have thourghly enjoyed using hide glue for a long time, but years ago I tried using a cold press "extra dark" PVA (I believe?) glue made specifically for veneer usage. What I found was that the glue leaked through some of the veneer pores or pin holes and did not in any way blend into the walnut veneer. The glue was very obvious. So for this reason I stick with hide glue because it is nearly invisible. However, if the blisters persist as I move forward, then my Plan B could well include the use of the adhesive resin you suggest.

I also do not use any commercial pore fillers because they never match the clarity that pure shellac does.

Thanks again for your suggestions and help,
Phillip

2/15/19       #7: Walnut Veneer Blisters ...
Tom Gardiner

John VB, I am not a fan of UF glue. I spent a few years hot pressing with UF and the off gassing was noxious, I would leave the shop with red eyes and a constricted throat. Sure, it bonded veneer but is susceptible to bleed through. The cure rate is fine in a hot press but cold pressing is way too slow.
I am currently trying to resurrect a hot press and plan to use type 2 PVA. The moisture in the glue along with misting the face makes the veneer pliable. My theory is that the faster closing and cure of the hot press will lead to reliable results with difficult layups.

Phillip, I don't think you are getting enough press pressure with 50# of weight. I watched as veneer lifted when my vacuum bag was at 20 psi. Of course the plattens will help but if your piece is of any size larger than one square foot then the veneer would be free to move. Maybe consider clamps and bars or spring poles (go sticks?) to increase the pressure.

2/15/19       #8: Walnut Veneer Blisters ...
NMPatriot Member

@Tom Gardiner

Thanks for your comments.

You could well be correct about my press not having sufficient weight to insure a good bond. Until recently, this system has never failed, but the recent blisters are a red flag that something is amiss.

As much as I do not need the distraction, tomorrow I will take another leaf of the same problematic walnut veneer and bond it using my above mentioned workflow changes. I want to resolve this adhesion issue and determine if my changes will be effective or not. Hopefully they will eliminate the blistering.

I have also attached an image depicting the blistering. For the sake of clarity: This veneer was meant to be used as a comparison between orange and super blonde shellac. I bandsawed the board in half so that the shellacs would not bleed together at the their common edge. It was difficult photographing the blisters so I added the red arrows to help point them out. I was aware of the many splits in this veneer leaf before I began the bonding process. I hope to see a better result with tomorrows test board.

Back to the veneer press: I really hope that my workflow changes will work because I am facing the application of two book-matched sheets, one quad-match and two single-leaf sheets on a large jewelry box I am currently working on. The use of weights would greatly simplify the bonding issue because the face and sides of this jewelry box are slanted outward top-to-bottom. If tomorrows bonding test fails to eliminate the blisters I will have no choice but to use cauls or clamps. And, yes, all sides are larger than one square foot.

Thanks again for your insightful comments and suggestions,
Phillip


View higher quality, full size image (800 X 600)

2/16/19       #9: Walnut Veneer Blisters ...
Pete

I have done some hammer veneering as well as plenty of lay ups in a vacuum bag. If I had the choice between the two, it would be the vacuum bag with a UF glue all day long. Now, there are some situations where hammer veneering is the only option- front face of chair backs comes to mind. If you are getting blisters, I would change up the glue consistency and temperature of room and substrate might want to be considered. For a flat panel like you have, you are now where near the amount of even pressure needed. For squeeze out, learn how to put the correct amount of glue on and there are additives to help prevent this with UF. There are some contributors that have responded to you and they do veneer work all day long for many years. I would listen to them. There are ways that work and do not work and its already been figured out...

2/16/19       #10: Walnut Veneer Blisters ...
Tom Gardiner

Your photo leads me to think that one of the contributing factors of the blisters is the splits themselves.
Here is what I think is occurring. Hide glue saturates the veneer with moisture expanding the veneer to it's maximum dimensions. You hammer it down and the glue gels with sufficient hold to adhere. As the moisture dissipates tension builds up in the veneer as it wants to shrink back to dry dimensions. Those fissures in the veneer allow local release of tension. I suspect that you will find the areas of blisters are essentially end grain. The glue bond is already poor in that grain orientation and the cracks allow the movement. I would test veneer without cracks to see if you had better success.
I believe the new formula for Unibond now has less or no UF. There was some grumbling about the change but that was a few years ago. Don't take my experience as gospel, there are a great number of veneer specialists who swear by Unibond.
You may have seen Vacuum Pressing System's web site and forum. If not, have a look. It is informative and may drag you into the twentieth century although I admire your desire to maintain traditional veneering.
Good luck and keep us informed about your progress.

Tom

2/16/19       #11: Walnut Veneer Blisters ...
NMPatriot Member

@Tom Gardiner

Thank you for your in-depth analysis of my veneer problem.

I took a look at the veneer fissures you noted with a 15x lighted loupe. The veneer appeared to me like twisted ropes laid together following a wavy pattern throughout. I was looking for endgrain, but did not see what I expected endgrain to look like. That may not make much so I took a closeup shot which is the first image attached below.

I also took a look at another test board with the loupe and I believe I could see the same twisted rope but to a much lesser degree. This particular veneer bonded to the substrate with no problems using my original workflow process. The last two images are of this test board. The first is a close up and the latter is the entire board. This test board has six coats of Super Blonde shellac, while the first only has two coats. (The blue circle is a reflection of one of my shop solor tubes.)

I will report back later with todays testing results.

Your help has been invaluable to me.

Thank you again for your help.


View higher quality, full size image (800 X 600)


View higher quality, full size image (800 X 600)


View higher quality, full size image (800 X 582)

2/16/19       #12: Walnut Veneer Blisters ...
rich c.

Have you looked into a different veneer supplier? I've never seen that many splits in walnut burl!

2/16/19       #13: Walnut Veneer Blisters ...
NMPatriot Member

@rich c

I was hoping I would never have to recall my experience with this veneer vendor, but since you brought it up ...

This veneer came from the first vendor I purchased veneer from 10-15 years ago. The website photos were so-o pretty, but when the order arrived the veneer lots were nearly all flakes with torn corners and edges and looked terrible. Mind you, this was my very first veneer purchase, but yet what I received was not at all what I expected. I consulted with another veneer vendor who after reviewing the images of what I received, noted that he had never seen such bad veneer.

After some haggling with the vendor they agreed to take all of the veneer back, but offered me a discount on whatever I wanted to keep, if any. The veneer you see in the photos in this thread is some of the veneer that I kept. So you nailed it - this is very poor veneer indeed.

As you may know, most reputable veneer vendors will chalk mark any defects in the veneer and you can purchase accordingly. This discounted veneer has worked well for some small projects, but the lot that the first image came from is very bad indeed.

I am looking at this veneer as a challenge and will know in a few days whether I can tame it or not. Any experience I can gain from this experience will be invaluable to me later on. No pain, no gain.

The veneer that will be used on the jewelry box I am currently working on was purchased from the vendor whom I consulted with and his veneer is superior. Live and learn. I will report back with my findings.

Thanks for your comments,
Phillip

2/16/19       #14: Walnut Veneer Blisters ...
NMPatriot Member

@Pete

Thank you for your comments and suggestions.

After my blister experience with this veneer leaf I am indeed making changes to my workflow many of which you noted and have been suggested to me from other posters. I am very grateful for everyones help.

For instance, I use a heating pad to heat my substrate and veneer before I begin. I am replacing the small round "hide glue" brush for a wider 2.5-inch flat brush which will allow me to get more hot hide glue (HHG) onto the workpiece in less time. I will use a heat lamp to keep my workarea as warm as possible. In addition, my new cauls should take care of the pressure problem.

I will know more in a few days.

I appreciate your help,
Phillip

2/20/19       #15: Walnut Veneer Blisters ...
NMPatriot Member

Yesterday I quad-matched a large sheet of veneer on a 16.5" x 24" board to test my updated workflow changes. Actually I simply quartered a large veneer leaf and rejoined it for this test. It was a very successful test. Not a blister in sight.

Thank you to everyone who pitched in to lend a hand. I sincerely appreciate everyone's suggestions and comments.


View higher quality, full size image (800 X 600)

1/5/20       #16: Walnut Veneer Blisters ...
Craig

Lose the HHG and go with a vacuum press and poly or UF glue.


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