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Need help diagnosing

1/17/15       
Mike

I had to veneer over an existing venerred top that was breaking apart from being so old. I bondoed the broken out areas and took a piece of 3/4" mdf over the top and the put the oak perpendicularly to the horizontal plane. I added pieces of veneer under the oak to help press down the center where the clamp wouldnt go. I took it off today 24 hrs later and its all rippeledbin the main area. About 4" around entire stop sign piece is flar but the rest is rippled. Its a bookmatched piece of crotch mahog that we had laid up locally.

What did i do wrong that it rippled on me? I used titebond yellow wood glue. The veneer had a wood backer.

Thank god we are a good refinishing company can can touch up where we sanded through after taking a hot iron and then a wet rag to try and steam out the indented areas.


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1/17/15       #2: Need help diagnosing ...
Mike

Heres a pic from the end so u can see the ripples


View higher quality, full size image (3264 X 2448)

1/17/15       #3: Need help diagnosing ...
Rich C.

Not enough clamping pressure. Get a vacuum bag. You can make your own bag, and vacuum pumps are around $100 at Harbor Freight. You'll have to gage it and add a valve to manually turn it off and on to hold the vacuum. If that doesn't work, you can park your truck on it. Buy a system to do it right. What's the cost going to be to spend money on labor to try and make it right?

1/17/15       #4: Need help diagnosing ...
David Thiessen  Member

Website: dtwoodworker.houzz.com

I have some observations based on the limited info and the picture you shared. 1) PVA glue doesn't stick to bondo very well in my tests. 2) The moisture in the PVA can cause the veneer to curl and buckle. This can be countered by spritzing the top side with distilled water to balance the moisture. Even better is to use a 2 part urea formaldehyde glue that will stick to bondo and does not have the moisture issues. 3) If I understand you right a 4" perimeter pressed fine but the rest wrinkled. From the picture it looks like it only flattened out where the clamps are. I don't think you had near enough pressure in the middle area to flatten out the wrinkles. You really need a vacuum press or some kind of a screw press to get the right amount of pressure evenly across the whole surface. I could see all three of these factors contributing to the problem. I don't know the condition of the old veneer but I probably would not have veneered over it. It would be better to have removed it and started fresh.

1/17/15       #5: Need help diagnosing ...
Mike

Both of your responses seem right on. I will have to see if i can talk the owner into buying a vac press

Thx again!

1/18/15       #6: Need help diagnosing ...
Tom Eaves

Mike best advice now cut your losses and start over. Go back to the place that lay up this panel and have then make over and press it for you. You will be money ahead yours and the customer. Sorry to say but that mahogany veneer will never lay flat. Mahogany is one hardest veneer to keep down even when using the right glue and press. Tom

1/19/15       #7: Need help diagnosing ...
John S  Member

When you say another company "laid-up" the crotch, do you mean made a single-ply face, or a laminated (2-ply or 3-ply) product? I'm assuming they gave you a single-ply veneer face and expected you to know how to press it. If they provided a 2 or 3-ply product, get your money back or a replacement. They did a poor job.

Pressing crotch Mahogany to a substrate (in my experience) requires a hot press capable of very high temperature (think 300 degrees F) and pressure (north of 100 lbs per sq in) and specialized adhesives (dry sheet adhesive). I don't believe you will ever be successful laminating single-ply crotch Mahogany with a vacuum press.

If you don't have the capability to press with the kind of temp and pressure I stated above, always purchase your crotch products in 2 or 3 ply form.

1/20/15       #8: Need help diagnosing ...
Rich C.

Gosh John S., I Googled your comment ("I stated above, always purchase your crotch products") boy howdy, you should see the results!

1/21/15       #9: Need help diagnosing ...
John S  Member

Now that's funny! :-)

1/21/15       #10: Need help diagnosing ...
John Costin

John S. wrote, "Pressing crotch Mahogany to a substrate (in my experience) requires a hot press capable of very high temperature (think 300 degrees F) and pressure (north of 100 lbs per sq in) and specialized adhesives (dry sheet adhesive). I don't believe you will ever be successful laminating single-ply crotch Mahogany with a vacuum press."

Seriously?

We have a hydraulic hot press. We use dry film adhesive. They are cool if you have the volume and the capital to support them. I have also personally pressed thousands of square feet of crotch veneer using vacuum technology with great success.

Sometimes it's more about know-how than equipment. Crotch veneer needs to be flat and supple. Sometimes it comes that way and sometimes it needs to be treated and flattened. I do agree that PVA is not a good choice for adhesive. Urea is really required for long-term stability. But I would not discourage small shops with vacuum presses and some veneer experience from pressing crotch veneer.

John Costin
Veneer Services Unlimited
vsu@gwi.net
207-985-7221
Custom Veneered Products for the Woodworking Industry.

1/21/15       #11: Need help diagnosing ...
John S  Member

I stand corrected (that's why I said "in my experience"). I just know that the thousand or so crotch Mahogany jobs I worked on were all hot pressed with dry sheet adhesive. The very few times I tried it with urea adhesives, the bleed-thru was quite bad.

1/21/15       #12: Need help diagnosing ...
John Costin

John S, rereading my post I want to apologize if it seemed a little harsh -- not meant to be. You did in fact share your experience, which is what this site is all about. I just wanted to let readers know that crotch is within reach for those with a little veneer experience and equipment.

Yes, bleed can be an issue with Urea, but we have found we can control it with blockers. DFA has its weaknesses, too. I've seen crotch shear the glueline and pull away from the backer on product laid up elsewhere. It makes me nervous, but we haven't done as much with it as it sounds like you have.

1/21/15       #13: Need help diagnosing ...
John S  Member

Hi John, no offense taken! I appreciate your responses because I know more today than I did yesterday, and that's exactly why I read these posts.

No matter how many times I've worked with crotch Mahogany, it still makes me nervous ... every time!

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