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View Dynamike's profile

cracking veneer problem

by Dynamike
posted 03-13-2018 04:38 PM


16 replies so far

View splintergroup's profile

splintergroup

2250 posts in 1337 days


#1 posted 03-13-2018 04:50 PM

A few questions, what was the substrate under the veneer? What glue did you use?
Any “unusual” ways the glue was spread or the veneer pressed?

From what I can see, it seems like the glue failed to adhere in the defect areas (aside from possible expansion, compression issues). Did you do anything to remove oils from the veneer before gluing?

View jbay's profile

jbay

2578 posts in 1013 days


#2 posted 03-13-2018 05:08 PM

Pre cat is a very strong finish. I spray just about everything with pre cat.
I have come across this several times in the past.
My conclusions are, and it may not be true, but it’s what I have found.

Seems to me that it only happens when 1- too many coats are put on and 2- they are put on too close together.
And I have only seen it happen on paper backed veneer.

My remedy has been to limit the number of coats to 3, maybe 4 at most.
(I also thin my pre cat more than recommended so I think I can get away with the extra coat.)
I wait at least a couple of hours between coats and I only put 2 coats on in a day.

I also only use wood on wood veneer.

Since I started using this practice, I haven’t seen this type of failure.

View Dynamike's profile

Dynamike

83 posts in 1453 days


#3 posted 03-13-2018 05:40 PM

@ Splintergroup

glue was rolled evenly with a rubber roller and rolled out with a veneer roller. no oils were present on either veneer.

-- "It's not scrap until it's sawdust", and maybe not even then...MAKwoods

View Dynamike's profile

Dynamike

83 posts in 1453 days


#4 posted 03-13-2018 05:48 PM

@ jbay
The old finish was a faux finish and I removed it completely down to the hardwood base. I tend to agree with you about the paper back. This is a scrap i’ve held onto. 10 mil paper. It does appear as tho the veneer is lifting from the paper. Only 2 nice even coats went on about an hour apart.

-- "It's not scrap until it's sawdust", and maybe not even then...MAKwoods

View Dynamike's profile

Dynamike

83 posts in 1453 days


#5 posted 03-13-2018 05:49 PM

-- "It's not scrap until it's sawdust", and maybe not even then...MAKwoods

View splintergroup's profile

splintergroup

2250 posts in 1337 days


#6 posted 03-13-2018 09:03 PM



@ Splintergroup

glue was rolled evenly with a rubber roller and rolled out with a veneer roller. no oils were present on either veneer.

-Dynamike

I’ve never tried contact cement after reading some of the FAQs on the joe woodworker site. It seems others have had success so I’d rule the glue as only a possibility for trouble.

From joe woodworker

VG15: My friend uses contact cement for veneering with raw wood. Should I try it?

There is one big problem with contact cement. It doesnt dry hard. Wood veneer is just as prone to seasonal movement as regular lumber and the ability of veneer to expand and contract with seasonal humidity changes is greater than the strength of the contact cement bond. I have tried every contact cement I can find and nothing offers the permanent bond required by a raw wood veneer. Contact cement is only good for paperbacked veneers and 2 ply wood veneers because the backing minimizes the veneer movement.

From a reader in Cleveland, Ohio…
“Here are the pictures of the banjo resonator. I used Weldwood contact cement. The resonator was glued and sat for one week before doing this. I put it out in the sun for about one hour. It heated up so it was noticeably warm to the touch. The back expanded but the veneer did not. The veneer pulled away from the sides of the back on the inside piece of veneer and cracked. The outside veneer pulled away from the bloodwood binding but not as much as the inside did.
I then put the back outside overnight to shrink the back. The back shrunk but the veneer rippled. The cracks did not close. The ripples were much smaller on the inside and cannot really be seen in the photo. The ripples on the outside are still there as seen in the photo. It has been 5 days since the experiment and the ripples are still there.”

View Tony_S's profile

Tony_S

905 posts in 3197 days


#7 posted 03-13-2018 09:14 PM


The old finish was a faux finish and I removed it completely down to the hardwood base.
- Dynamike

So the original tabletop was solid wood of some description?
If so, that’s what the problem is, and you won’t be able to repair it or keep it from continuing.

Paper backed veneer is a very stable product. It doesn’t agree with unstable or even semi-stable surfaces at all. Particularly when used in conjunction with contact cement.

-- It is the mark of an educated mind to be able to entertain a thought without accepting it. Aristotle

View Tennessee's profile

Tennessee

2880 posts in 2629 days


#8 posted 03-13-2018 11:18 PM

I did quite a bit of veneer repair back in the late 70’s and 80’s when I had my refinishing business.
I truly believe that the contact cement is failing to hold the veneer, and allowing it to rise wherever moisture can get through to change the veneer and make it warp.

Even the best finishes only stop about 60% of the moisture, (correct me if I am wrong on that), so some moisture will get through, both through the top finish, and slowly through the base wood underneath.

The contact cement is flexible, not solid, so the veneer can move with moisture, as you are seeing.
I think this is going to be a do-over. Shame, it is a beautiful table, and sapale makes a wonderful veneer top.

-- Tsunami Guitars and Custom Woodworking, Cleveland, TN

View shipwright's profile

shipwright

8055 posts in 2912 days


#9 posted 03-14-2018 12:01 AM

If you want a good veneer job I would suggest real veneer (solid wood, not paper backed) and a real veneer glue (hard drying like hide glues and urea formaldehydes.
Just my opinion…..
I would only use paper backed over something extremely stable like plywood or MDF.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese! http://thecanadianschooloffrenchmarquetry.com/

View jerryminer's profile

jerryminer

939 posts in 1556 days


#10 posted 03-14-2018 03:14 AM

The substrate is solid hardwood?
Does the grain run across the table—rather than along the length?
If so, you’ve created a real problem that probably can’t be “fixed” without a re-do. The hardwood will move across the grain, and if the veneer doesn’t move with it, the conflict will create issues such as you see.
I think you’re getting good advice above about contact cement vs. other glues

-- Jerry, making sawdust professionally since 1976

View jbay's profile

jbay

2578 posts in 1013 days


#11 posted 03-14-2018 01:40 PM

I have seen this exact same thing on 1/4” sheets with a mdf core.
I agree putting the veneer over the hardwood is never good, but I don’t think it’s the reason for what we are seeing with the lifting.

I’ve had other shops ask and show me the same problem with different materials, glues, and substrates.
The common denominator in all cases was the pre-cat lacquer.
The only other thing close, is the paperbacked veneer. It is thought that the pre-cat lacquer soaks through the veneer and loosens up the glue layer between the veneer and the paper and as the pre cat cures it shrinks and pulls the veneer together causing what we see here.
You can blame everything else but you should at least consider the lacquer possibility.

Everybody has there own conclusion,
I’ve been there and done that, talked to many people in the trade about it. This is just mine.

On another note about contact cement. I have used hundreds of gallons over the last >25 years.
I can’t recall 1 call back to do a repair.
Don’t ask me why. Maybe it’s the brand, application, climate, usage..IDK
But I have used it ALOT without the stories I hear everybody tell.

View Dynamike's profile

Dynamike

83 posts in 1453 days


#12 posted 03-14-2018 02:09 PM

I thank you all for your thoughts and advice, but I’ve got a decision to make and I can’t apply everyone’s thoughts or fixes…you’ve all got great suggestions but which one’s are going to solve the problem? I don’t know. The obvious thing here is that it’s going to have to be redone a different way. The definition of insane is doing the same thing over and over and expecting a different result right?

-- "It's not scrap until it's sawdust", and maybe not even then...MAKwoods

View jbay's profile

jbay

2578 posts in 1013 days


#13 posted 03-14-2018 02:17 PM

At this point with all the variables of multi layers of veneer over hardwood, and the labor to strip them off and the cost of materials to start over. Your best bet would be to make a new solid top out of sapele.

View jbay's profile

jbay

2578 posts in 1013 days


#14 posted 03-15-2018 02:34 AM

Here is something that will help you identify the problem, or leave you more confused.

View Tennessee's profile

Tennessee

2880 posts in 2629 days


#15 posted 03-15-2018 12:36 PM

Well, if the general consensus is you are in the arena of a do-over, jbay might be right – do the top in solid sapale. At least you do not have the worry again about veneer problems of any kind.

Personally, I have bought one huge load of sapale wholesale, almost gone now. Used it in a lot of guitars, very tonal. Great wood, but to be honest, a bit of a tendency to dent. Looks a lot like African Mahogany but not as hard or dense. Might not be the best wood for a solid top. But I think you definitely are at least pulling off the veneer, as you have no real way to repair what is happening.

-- Tsunami Guitars and Custom Woodworking, Cleveland, TN

View rwe2156's profile

rwe2156

3068 posts in 1595 days


#16 posted 03-15-2018 02:58 PM

Paul,

Wouldn’t you need a vacuum press for a job this big?

How would approach it using the correct glue?

-- Everything is a prototype thats why its one of a kind!!

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