Veneering Disaster, recovered I think.

[sawdust maker]

I'm making a mahogany cupboard with veneered sides and top. The method I was using was to glue the veneer in a press with PVA glue.

I spread a thin layer of PVA on the side.

The veneer was then placed on top. To stop the veneer sticking to the top board of the press I covered it with plastic bags.

Put the top board on and screwed it all down.

After about two hours I opened the press up to check that the press was doing it's work and found this.

The water in the PVA had caused the veneer to expand and wrinkled away from the substrate, also lots of glue had seeped through the veneer. Clearly the press was not working. The only places where the veneer had remained flat was directly under the bars of the press. Something had to be done and quickly. I have an old clothes iron I use for iron-on edging. With this at it's highest setting I set about ironing the veneer, after first wiping away the glue that had seeped through the veneer with a damp cloth. The result appears to be quite good.
I've heard of using an iron with PVA glue, but that method is to put the glue on both the veneer and substrate, let it dry and then place the veneer in place and use an iron melt the glue and stick the veneer down. What I did was to use the hot iron to cure and dry the glue. Any thoughts anyone. Has anyone done it this way?

 

[doctor Bob]

I'd anticipate issues with finishing because of the glue saturation.

 

[Random Orbital Bob]

Aren't you meant to use contact adhesive for veneering

 

[woodbrains]

Hello,

Ironing PVA whilst still wet is something I used to do occasionally for small veneering jobs. It is more to do with evaporating the wateri in the glue, rather than softening the glue film, as in hammer veneering. As long as the water does not evaporate too fast and cause splits in the veneer it works OK, but there are much better ways.

Your press method is the better solution, but you have made a few errors that you should fix next time.

You have used far too much glue. Try a mini roller handle with a foam roller head, instead of a filling knife. Spread the glue so it is covering the entire substrate, but not any thicker than the roller can spread by pushing quite firmly, not as though you were actually painting.

You do not have a thick enough board on top. It should take quite a few layers of 18 mm mdf ar such. The clamping battens will distribute the pressure at 45 degrees to their edges, so you need enough thickness of pressure boards, so that the pressure from each batten will overlap. In your case, there would have been no overlap, and in fact large spaces with no pressure at all.

You could also try curving the battens so that they touch the centre of the stack ( like the rocker on a rocking chair ) ant the clamping bolts then pull the edges down. This ensures pressure will rah right across the boards. The curvature only needs to be a slight, perhaps 1/8 in per foot.

Hope this helps,

Mike.

 

[sawdust maker]

Thanks Mike that is very useful advice. Looks like I got it all wrong apart from curving the bars slightly, which I did. Doctor Bob said I might have problems when I come to putting a finish on. Thankfully the veneer I've put on can be on the inside. I'm off now to make a much better press and I'll use much less glue next time.

 

[woodbrains]

Hello,

Sorry couldn't see the curved cauls. You were not too far wrong really, it'll work next time, I'm sure.

Mike.

 

[sawdust maker]

Taken Mikes advice and improved the press. I've added another bar and placed three boards of 18mm chipboard and 15mm MDF as pressure boards. I also used a roller to lay down the glue, much less is applied by this method than my way. I used a layer of thin plastic to prevent the veneer sticking to the press.

 

[andersonec]

Do not use contact adhesive!!!!!!

As Mike said, far far too much glue especially when it is thin glue like PVA, if you intend to do a lot of veneering then you may want to try

http://www.axminster.co.uk/titebond-col ... for-veneer

It is a lot thicker and goes a long way to prevent bleed-through but you still have to use it sparingly though.

You may also want to use some form of cushioning between your veneer and press, some sort of thickish material like a few layers of felt or a piece of an old smooth blanket, this will fill any potential gaps between veneer and caul, place it on between your plastic bag / greaseproof paper and caul.

Andy

 

[Giff]

I have found wide cling film works, which can be overlapped, instead of plastic bags. Geoff

 

[woodbrains]

Hello,

That revised press looks great, should work well. The glue for cold press veneering, as suggested, is good stuff.

Mike.

 

[TRITON]

Too much glue
Spread a thin layer and allow it to sit for 10 mins. Then add a little more about the areas that have obviously absorbed most. It avoids something thats called 'glue starvation' You dont need a lot and if its surface dried a tiny bit then thats fine.
I use about 4 sheets of greaseproof paper before a 2nd pressing board prior to clamping up. The 2nd pic with lots of clamps is the way to go.

Didnt see it mentioned but do you know that you shouldnt really use straight pieces of timber as your clamps. The clamping at the ends lifts the middle. To avoid this you do the down facing side of the baton in a very slight curve. As you tighten the ends the bar puts maximum pressure into the center of the board and the flex means the edges are clamped just as tightly :?

For ironing on veneer using pva ,you need to allow the glue to dry nearly completely. You dont want any amount except a small percentage of water in it. Then a sheet of greaseproof or brown paper and a hot iron.
Its tricky on curves but as long as you keep in mind not to hold it on to long and try to have the 'ironed' section cool down as quick as possible. A veneer roller is a must have.

Not sure if this will come out due to my few posts but ive a table i did in burr Madrona. Flat surfaces are easy, try a compound curve :lol:
Used the iron on technique as clamping just wasnt an option :lol:

 

[sawdust maker]

The man's a genius...................Not me - Mike. Following his advice, look what I got

No bleeding through, perfectly flat and all stuck down.

Thanks Mike

 

[TRITON]

Looking good 8)
Now when are we going to see the completed cabinet

 

[sawdust maker]

The post is on Projects forum, TRITON - Hall Cupboard.

 

[deserter]

Don't really want to upset the apple cart too much, but Mike's got it spot on, ignore anything different.

 

[woodbrains]

Hello,

Well done, that looks great! =D> =D> =D>

Mike.

 

[woodbrains]

Hello,

Just a thought, because you said the mahogany side was the inside. Are you veneering the other side too? You'll need it to balance the veneer on the inside, or the panel will cup. Ideally it should be done at the same time. If you have not, I suggest you place the newly veneered board, veneer down on several layers of newspaper, on a flat board or bench. This is a good dodge for avoiding using a balancing veneer, but you'll need to do something to avoid the cupping.

Mike.