Help! Veneer failed to stick

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tiredofspam

Naaaah. 110 feet is enough. :-)

You are absolutely correct. 14.7 psi is the theoretical maximum achievable with a vacuum bag; in practice, a bit less, maybe 14.5.
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On 11/20/2012 5:13 PM, graham wrote:

You have a better vacuum pump that I do. Best mine can do is 14.7 psi...
:)
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On 11/18/2012 8:23 AM, graham wrote:

Did you rough up the mdf surface a little? I had glued some mdf w/epoxy and it didn't stick. That indicated to me that either too smooth, or a release agent inteferred.
I sanded w/220 the next time same batch of mdf and tried again. No problem.
I still don't know why... but a mechanical bond and removing whatever might have been on the surface cured the problem the next time.
It was an expensive lesson, as the veneer was ruined (ETIMOE curly) like this http://tinyurl.com/bqdxaop
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On 11/18/2012 12:16 PM, tiredofspam wrote:

I should mention that my situation happened with a vacuum bagged setup.
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tiredofspam wrote on 18/11/12 17:16:

Thanks for the idea - yes, I did sand the substrate (ply, not mdf). I can relate to the expensive lesson. At least I have a couple of spare sheets. I knew I should have done some practice runs but I was too enthusiastic..
g.
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On Sun, 18 Nov 2012 17:27:02 +0000, graham wrote:

Being a Neandertal, I have to suggest using hot hide glue and a veneer hammer next time. No clamps required. If it gels too fast add a little urea.
But practice on scrap first. It does take a little getting used to.
--
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And if it begins to lift, you can put it back down with heat and pressure. BTDT.
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"graham" wrote in message
Hi All,
I've just veneered a sheet of birch ply (one side ash, one side ash burr) and when trimming the edges in places the veneer flaked off the glued surface. I think that I could probably peel chunks off, a bit like a nasty bit of far eastern ply.
Inevitably I'm wondering what I did wrong.
The panel is ~700 x 250 mm. Glued with cascamite, applied with a toothed spreader then went over it with a sponge roller (apparently it's important not to have too much glue as it can push through the veneer). With the veneer positioned I placed it on a piece of MDF and then stacked a pile of MDF sheets on top.
My guess is that there wasn't enough pressure to force a thin glue line: so either (i) more pressure; and/or (ii) mix the glue a bit runnier.
Am I on the right track? If so how much pressure am I going to need? Curved cauls + cramps? Vacuum bag?? Is there something fundamental I've missed??
And am I right in thinking that this piece isn't usable :( as the veneers could delaminate in the future?
The only time I used Veneer was about 25 years ago. Covered all the interior doors and door trim with mahogany. Used contact cement. All is still intact. WW
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