Help! Veneer failed to stick

[graham]

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?

g.

[dadiOH]

How long was it under weight and how much flaked off when trimming? Flaked off cross or with grain?

[dpb]

On 11/18/2012 7:23 AM, graham wrote: ...

Indeed. You need either a press or at a minimum cauls/clamping. You need something at a minimum of 50psi which translates to a lot of total force over a larger surface.

A useful general paper on using--

--

[graham]

12 hours

a couple of corners; one a triangle with sides 2cm x 2cm along the panel edges (this the burr veneer)

g.

[tiredofspam]

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

[tiredofspam]

[graham]

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.

[Larry Blanchard]

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.

[WW]

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

[Doug Miller]

Larry Blanchard wrote in news:k8b7n2$1gv$ [e-mail]:

And if it begins to lift, you can put it back down with heat and pressure. BTDT.

[dadiOH]

Obviously, the veneer isn't glued solidly. There could be lots of reasons but if I had to guess I'd guess insufficient glue.

If it were me, I'd try checking that thought by gluing a small piece of veneer - 2" x 6", eg - on each of two substrates; glue the first as you did originally, the second with a much more generous amount of glue.

Another though is in the mixing of the glue. The only one of that type I've used is a dry powder that one mixes with water to a creamy consistency. "Creamy consistency" is pretty subjective...perhaps you used too much or little water? I'd check that thought too by mixing up some glue using varying amounts of water.

Other thoughts include the fact that the glue has a finite shelf life, that it needs to be at least 65 degrees to cure and that 12 hours is at the low end of cure time - 18 to 24 is safer.

[graham]

Good ideas - I shall experiment. I've used this glue lots, and it was mixed as per instructions and how I would use it for normal joints. But now that I think about it I recall mixing it a bit runnier when I was butt jointing 4x2 for the bench top, I think because I had some notion of the water being absorbed overly quickly, though it may have just increased working time before all the clamps were in place.

New glue. The tub specifies 6 hours @15 degrees (C), and it was more like 20 degrees (C) (~68F?).

I shall experiment (and also work out the best route to more pressure cost effectively)

thanks, g.

[graham]

Thanks for the reference.

I followed up on vacuum presses (expediency vs accruing hide glue & hammering skills).

I read up at

but the price of equivalent looking pumps here in the UK seems ridiculous (>£400), unless I'm looking in the wrong places.

Does anyone know where to get a dry running vacuum pump in the *UK* at a sensible price?!!

Also, isn't 50psi more than an atmosphere?

rgds, g.

[Sonny]

1 atmosphere = 14.6959488 pounds per square inch

Sonny

[dadiOH]

I've never done this but think it should work well and I'll probably do it someday...

The peoblem in gettring enough pressure is not at the edges - that is easy - but at the center. Cauls help that, vacuum press is ideal but can be pricey.

My idea involves dense foam rubber. By "dense" I don't mean rigid, but squishy, just not real squishy. The sequence, bottom to top...

1. 3/4 ply

1. subststrate

2. veneer

1. cover sheet (brown wrapping paper would serve

2. 3"-4" thick foam

1. 3/4 ply

Clamp along all edges to bring top & bottom ply close together. That will squish down the foam in the central areas and although the pressure there will be less it will be even and should be sufficient as long as the width isn't enough to seriously bow the top/bottom ply.

[Sonny]

Am I missing something, here?

His project is 250mm X 700mm, or about 10" X 27". There shouldn't be a great problem properly clamping the veneer to the substrate without going through extraordinary means, i.e., special clamping, extending/extended cauls, etc.

Or is he trying to veneer a whole/half sheet of ply, then later cut that sheet into one or more 250mm X 700mm units?

Initialy he says sheet of ply (implying whole/half sheet?), then he uses the term panel (only the 250mm X 700mm unit?).

Sonny

[graham]

dadiOH wrote on 20/11/12 17:39: >

Interesting idea. Strikes me as quite tricky to get foam of the right density.

Sonny wrote on 20/11/12 18:10:

problem properly clamping the veneer to the substrate without going through extraordinary means, i.e., special clamping, extending/extended cauls, etc.

into one or more 250mm X 700mm units?

term panel (only the 250mm X 700mm unit?).

I didn't mean to imply the entire "sheet". So panels cut to size then veneered.

So yes the panel being veneered was 250x700, the next (and largest) is

600x700.

What would you suggest clamp-wise in order to distribute the force evenly?

g.

[graham]

yes, which is far less than the 50psi dpb suggested.

50psi doesn't seem unreasonable compared to normal jointing pressure, but is completely unachievable with a vacuum press. So my point really was what is the required pressure for glueing veneer? (as vacuum presses clearly work!)

g.

[tiredofspam]

Are you kidding. 50psi is easily achievable in a vacuum bag.

[dadiOH]

Things of those sizes should present zero problems in clamping, any type will do. Probably even little spring clamps if you used a bunch of them.