Veneer vacuum bag glue?

[sihollies]

A quick question if I may?

I'm sure this is a very basic question to most here, but can I use standard PVA glue in a veneer vacuum bag & if not, what adhesive would should I be using?

I am a hobbyist & can't justify buying an electric press, so have recently bought a Roarocket system & am planning to experiment with it in the very near future, so thus, I am asking the question.

As always, many thanks in advance

Simon

 

[Sgian Dubh]

... can I use standard PVA glue in a veneer vacuum bag & if not, what adhesive would should I be using?

Yes, although there are formulations such as Titebond Cold Press Veneer Glue that are designed for the purpose. Personally, I've not found any great advantage in using these more expensive veneer formulations over regular PVA, except perhaps somewhat extended open time. Slainte.

 

[Torx]

I’m pretty sure Bagpress do their own recipe - whether it’s anything much different from off the shelf PVA I don’t know. What I did find amazing when I saw it demonstrated is that he let the pressure off after only a couple of minutes and it was solid (bendy ply over wave like form).

 

[sihollies]

Many thanks both, it's greatly appreciated!
I will be having an experimentation session tomorrow thanks to your input.

Again, thankyou!
Simon

 

[Hornbeam]

I use either Titebond extend or aerolite one shot. Both work fine, Aerolite is better for long open time and more waterproof finish but needs a long vacuum time

 

[Sgian Dubh]

I’m pretty sure Bagpress do their own recipe - whether it’s anything much different from off the shelf PVA I don’t know. What I did find amazing when I saw it demonstrated is that he let the pressure off after only a couple of minutes and it was solid (bendy ply over wave like form).

I wonder if that demonstration included the use of a heated press? Do you know?

Heat applied in a press or bag to the veneering job or to a bent lamination greatly increases the speed of cure for adhesives. The normal calculation for a press that operates at ~60ºC is to allow for pressure to be applied for one minute per millimetre of thickness, plus allowing a bit of time for heat to build up. Therefore to bond standard 0.6 mm thick veneer to substrate reckon on allowing about one minute. I've always allowed a bit more time than that, perhaps four or five minutes. It's trickier with laminated forms in press or bag because it can take longer for the heat to spread through the bending form and the lamination, and the temperature may not be consistently at 60ºC, but at something lower, or even perhaps higher. So, for example, I've always tended to leave something like an 18 mm lamination in the press for between thirty minutes an an hour rather than the 18+ minutes the allowance I described above suggests. Slainte.

 

[Stevekane]

If anyones wants to have a go at vaccimm pressing I have what I think is a dental vaccumme pump that a mate used to laminate curved kitchen cabinete doors. I know nothing about it, its a chunky little thing about from memory about 6ins square, not even sure if its just a pump without a motor to drive it, but Im happy to dig it out for anyone that wants to know more, Im happy to swop it for a beer token.
Steve (nr Bournemouth)

 

[Torx]

I wonder if that demonstration included the use of a heated press? Do you know?

Heat applied in a press or bag to the veneering job or to a bent lamination greatly increases the speed of cure for adhesives. The normal calculation for a press that operates at ~60ºC is to allow for pressure to be applied for one minute per millimetre of thickness, plus allowing a bit of time for heat to build up. Therefore to bond standard 0.6 mm thick veneer to substrate reckon on allowing about one minute. I've always allowed a bit more time than that, perhaps four or five minutes. It's trickier with laminated forms in press or bag because it can take longer for the heat to spread through the bending form and the lamination, and the temperature may not be consistently at 60ºC, but at something lower, or even perhaps higher. So, for example, I've always tended to leave something like an 18 mm lamination in the press for between thirty minutes an an hour rather than the 18+ minutes the allowance I described above suggests. Slainte.

I’m 99% sure it was cold, perhaps it was ‘good enough’ to risk taking it out for demonstration purposes, but would normally be left for longer as you describe?

 

[Sgian Dubh]

I’m 99% sure it was cold, perhaps it was ‘good enough’ to risk taking it out for demonstration purposes, but would normally be left for longer as you describe?

Perhaps your good enough comment is correct but I obviously don't know.

As an aside it's my experience that PVA adhesives aren't always a good choice for curved laminations because of their creepiness: there's a tendency for laminations to spring back or straighten following the glue line, especially those with very tight curves where the glue line is under greater stress than gentle curves. The laminates can also slip across its width if stress is applied to a small part of the edge's cross section, e.g., where slots or grooves are cut in a laminate's edge to hold the steel inserts of seat webbing.

It's sometimes a good or better choice for bent laminated work to select a non creeping adhesive for a more rigid end result. Urea formaldehyde and epoxy resin are just a couple of non creeping types of adhesive, for example. Slainte.