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Old 27th December 2006, 08:44 AM   #1
suzyj is offline suzyj  Australia-Aboriginal
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Default Help! Cracks opening in my veneer

Hi guys,

A month or so, I finished (so I thought) a pair of speakers with crown cut birch veneer. I used plain veneer (no paper backing) and applied it with the PVA and iron method. I applied two coats of PVA to the cabinets, waited for it to dry, then ironed on the veneer.

It all went swimmingly well. I finished the speakers with carnauba wax and was happy.

Yesterday, I put the speakers in their final position on the desk in my study. They got some afternoon sun, and cracks started opening all over the place.

I've just spent a couple of hours removing the veneer and sanding the cabinets back to remove the PVA, and am getting ready to do them over (I have heaps of veneer left), but I'd like some tips on where I might have gone wrong.

Should I try contact cement rather than the PVA? Maybe hide glue? Maybe coating the veneer as well as the cabinets?

Regards,

Suzy
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Old 27th December 2006, 11:31 AM   #2
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The veneer may well have had too much moisture, and cracked when it dried out. Was it stored outside? You may want to bring it in and let it acclimatise for a week or so before you try again.
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Old 27th December 2006, 01:41 PM   #3
rabbitz is offline rabbitz  Australia
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What a shame as they had a great finish.

Sounds like moisture content in the veneer. You might want to have a look at some of the wood working forums as they have some great tips and hints. They normally use some animal type glue (can't remember what it is) that has to be heated and stinks like hell. Rivergum veneers recommend a polyurethane glue that's used in boat building. Both of those require clamping or some sort of vacuum system.
http://www.rivergumtimbers.com.au/sh...s&IDCategory=3

I was told by another DIYer yesterday that contact adhesive is not a good method for timber veneers... an article somewhere and don't know the details.

I tend to seal the cabinets after completion with a clear polyurethane like Estapol but others like Danish Oil.

Good luck with it.
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Old 27th December 2006, 04:18 PM   #4
poobah is offline poobah  United States
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1) Make sure the veneer is as dry as possible before ironing it in place. The PVA will also cause expansion. The good thing is that the PVA can "dry" for several days before ironing.

2) It is fairly easy to compress the wood as you iron it on. Iron down one edge, push the other edge to create a buckle and iron it down, then place a flat board over the whole mess to spread the buckle out evenly, and iron it all down.

3) As an alternative (perhaps the best one) to the compression trick, work the iron very slowly from one edge to the other... as you would mow a lawn. This allows time for the wood to shrink (from the heat of the iron) before it is actually locked in place.

4) Your veneer may also be rather thick... dont be afraid to really sand it down good. A thinner layer may be more inclined to stretch rather than fracture.

5) Use a polyurethane finish... much better at stabilizing (locking in) moisture content in the veneer.

Good luck... veneering is BLACK science.

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Old 27th December 2006, 04:30 PM   #5
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Default Re: Help! Cracks opening in my veneer

As others have said, the moisture content in the veveer was higher at some time before being exposed to the sun. The heat from the sun dried the veneer, possibly even softened the glue somewhat and caused cracking.

I believe from your description in previous threads that the method of application was fine.

You can try using a finish that will seal the wood from rapid/ excessive moisture changes. Surface finishes like lacquer and varnish will do a good job. Most drying oils like tung and boiled linseed somewhat less so. Shellac and raw linseed oil even less. Paste wax alone does absolutely nothing to stop transmission of moisture.

Also make sure the veneer is very dry before application. Keep it in the general area where the speakers will be used for about a week before application. Ensure plenty of airflow for each sheet while the veneer acclimates.

Try to keep the finished speakers out of direct sun. Even the finest, most skilfuly crafted vennered furniture can exhibit the same problems if exposed to direct sunlight no matter what method one used to apply the veneer. It's bad for the drivers too!

Hope this helps.


Quote:
Originally posted by suzyj
Hi guys,

I've just spent a couple of hours removing the veneer and sanding the cabinets back to remove the PVA, and am getting ready to do them over (I have heaps of veneer left), but I'd like some tips on where I might have gone wrong.

Should I try contact cement rather than the PVA? Maybe hide glue? Maybe coating the veneer as well as the cabinets?

Regards,

Suzy
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Old 27th December 2006, 05:39 PM   #6
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Default this works

Suzy- I had similar problems with the first pair of speakers I veneered (also birch). The last pair I built, I use polyurethane glue. I don't know if it is available where you live, but it is clear and light brown in color. It expands when it dries, into hard yellow bubbly material if it is not compressed. You need to clamp it when it is drying, I have found that using a 1/2 inch thick piece of foam cut to the exact size of the speaker panel works best to evenly distrbute the clamping pressure. Line up the foam with the edges of panel (you will get a little hill at edges if the foam is larger than the panel).
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Old 27th December 2006, 06:09 PM   #7
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oh, I meant to mention that depending on the thickness of your veneer, it might be possible for the PU glue to bleed through. If that happens, the veneer will not accept stain evenly. You can prestain the veneer.
I've only used this on paperbacked veneer, which had no problems with bleedthrough. It came out much, much, smoother than using contact cement and ironing.

JJ
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Old 28th December 2006, 05:42 AM   #8
suzyj is offline suzyj  Australia-Aboriginal
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Thanks for the advice guys. I've redone the top of each speaker. The procedure I'm following is as follows:
[list=1][*]Cut a piece of veneer about 3mm oversize on all edges.[*]Sand the cabinet MDF surface with 120 grit emery.[*]Coat the cabinet with a generous coat of white PVA using an old paintbrush.[*]Let it sit for an hour.[*]Coat with a second coat of white PVA.[*]Coat one side of the veneer with PVA.[*]Spray the other side of he veneer with a little water, to keep it from curling.[*]Leave everything overnight inside the house (with a dehumidifier running) to let it dry completely.[*]Set the iron to the 'silk' setting.[*]Iron the veneer onto the cabinet starting on one side, and slowly going across to allow the veneer to shrink without cracking. It's important to go across the grain, as otherwise the veneer isn't able to shrink and will crack.[*]Trim the veneer about a millimetre away from the edge of the cabinet with a scalpel.[*]sand it flush with the cabinet using 120 grit emery.[/list=1]

The result so far is really well bonded veneer, with a perfect 90 degree edge. I think the moisture content is low enough so that cracking won't reoccur (touches wood).

<sigh> I guess the good thing about stuffing up so royally the first time is that I have more experience when I redo it.

Cheers,

Suzy.
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