How dry doe a 3-4mm 'veneer' top need to be?

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Toby Park
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Joined: Sun Jun 02, 2013 8:53 pm

How dry doe a 3-4mm 'veneer' top need to be?

Post by Toby Park »

Hi all,

If I were to glue a 3-4mm walnut top onto a 40mm thick piece of ash, does it really matter if the walnut has not been properly dried? (the ash will of course be dry).

I can't see that such a thin top could warp if it's well bonded to the ash...?

**could moisture cause any issues with finishing? (tru-oil & wax)
**could the moisture negatively affect the ash in any way?
**If I had a 100mm x 100mm cavity within the ash (i.e. a 10cm x 10cm section of walnut which is not bonded or supported by the ash below) could this small area start to warp, even if tightly bonded everywhere else?

I don't have any idea how dry the walnut will be, but lets say worse case it was cut from fresh into a 4mm top, and left in a reasonably dry house for 9 - 12 months before being glued to the ash.

Many thanks!!

Eric Baack
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Re: How dry doe a 3-4mm 'veneer' top need to be?

Post by Eric Baack »

The walnut may crack as it shrinks and the ash does not.

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Barry Daniels
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Re: How dry doe a 3-4mm 'veneer' top need to be?

Post by Barry Daniels »

In 9 to 12 months, the walnut would be plenty dry.
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Craig Bumgarner
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Re: How dry doe a 3-4mm 'veneer' top need to be?

Post by Craig Bumgarner »

One way to check is to weight it on a gram scale. Assuming the space where it is stored is ~ 30% RH, once the weight is stable, the piece should be ready to go. A humidity monitor is a must, $10-$20 at the hardware store.

Craig Bumgarner
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Re: How dry doe a 3-4mm 'veneer' top need to be?

Post by Craig Bumgarner »

Oh, consider using epoxy to glue, not a water based glue or as it will swell the veneer and it may check later on. (don't ask how I know this).

Toby Park
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Re: How dry doe a 3-4mm 'veneer' top need to be?

Post by Toby Park »

Thanks,

Apparently it's been drying for the best part of a year, and it will probably be the best part of another year before I use it,

I've heard that 1 year per inch of thickness is a good rule of thumb, so 1.5 years for 3.5mm sounds like plenty, so hopefully I won't have any problems there.

Craig - does your advice stand regardless of how dry the wood is? I normally just use regular titebond, (an Aliphatic resin emulsion, according to their site, but an emulsion in what? water?) - any reason why titebond would be an issue for such a thin piece? the stuff is so strong I can't imagine it lifting, but who knows.

gene downs
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Re: How dry doe a 3-4mm 'veneer' top need to be?

Post by gene downs »

I can't remember his name at the moment, but some famous builder said in his book that he uses contact cement to glue veneers of this sort. Has anybody actually tried that? I seems like you would get a rubbery glue line that wouldn't take finish well.

David King
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Re: How dry doe a 3-4mm 'veneer' top need to be?

Post by David King »

I refinished a guitar that had the veneer glued down with contact cement. Don't do it. I had to melt off all the veneer and scrape the glue off before I could surface sand and apply new veneer with urethane glue. Titebond wouldn't be my first choice due to the moisture it introduces.

John Catto
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Joined: Sun Jan 08, 2012 7:54 am

Re: How dry doe a 3-4mm 'veneer' top need to be?

Post by John Catto »

One of the traditional ways of applying veneer is to use what they call "Glue Film". You place the film between the wood and the veneer and use an hot iron to melt the glue. I used it (on the advice of a veneer company) years ago on a couple of projects and it worked really well. I still have the guitar 14 years later and it hasn't moved at all in that time. One thing to watch out for, don't cut the veneer too close to final size since it will shrink dimensionally when you heat it with the iron. On the other hand I've used Titebond without any issues , just use a full body template as a caul. I can see why people would be wary of it but you use moisture to flatted veneer before you apply it so that's already there.

What doesn't work is epoxy, I tried that before using the glue film, several tries and it was terrible, whatever I did I got bubbles, adherence issues, all kinds of problems. Don't bother.

This is the stuff I'm talking about

(Auction link removed by staff - sorry, links to active auctions are prohibited by our Policy )

http://img.photobucket.com/albums/v436/ ... 010052.jpg

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