Impact Adhesive vs Contact Adhesive

[Calpol]

Not been on here for ages... Not had much to ask :lol:

Anyway, I'm veneering the front rail on my Demi-Lune table, the college uses contact adhesive for it but the only one I could find in the shop was impact adhesive. It says it's fine on wood but wondering what the difference was?

Thanks all

 

[Chris Knight]

Same stuff.

There are variations within the species however. You can get a non-solvent type these days (in fact it is the only kind some stores sell to avoid problems with little glue sniffers) but most are based on strongly smelling solvents.

In my experience, these are better and stronger glues. You can get varieties that allow a certain amount of repositioning before everything is finally stuck for good and these work pretty well with no loss of final strength - I use Evostick Timebond in this category for most of the gluing I do with contact adhesives.

I am not a fan of using any contact adhesive for veneering although there is no doubt it can be useful at times. My preferred method is (if I cant press it in a my vacuum press), to use the dry bonding technique with PVA and a household iron - it works very well indeed.

 

[Paul Chapman]

I'm not a fan of impact/contact adhesives either. Used to use them a lot back in the 1970s when Formica was all the rage. In my experience, if you are using it on something that you want to last for years, you need to be careful. The adhesive can completely dry out over a period of years and the veneer, laminate or whatever can lift off. If it is an important job and you want it to last, I would use something else.

Cheers :wink:

Paul

 

[woodbloke]

Agree with Paul and Chris here. Impact or contact adhesive is good for fixing laminates like Formica but I certainly wouldn't dream of using it for gluing veneer. If you are making a demi-lune then it could be pressed in the airbag providing a suitable mould was made...you would also need to have a much smaller base board to allow the bag to suck down closely to the former - Rob

 

[Calpol]

Hmm, thanks fellas

The college has a new press now, don't even know if it's set up yet though. It's one of those huge jobbies with the rubbery membrane thing that you lower onto the veneered component, I think it has UV lights as well... That any good?

Obviously can't do that at home though! But if these impactish glues aren't excellent then I'd really rather not use them. I've spent a good few hours getting the veneer all cut (and it looks awesome :lol and really don't want to waste it! Burr walnut, black lines and kingwood cross banding if anybody's interested? BUT it needs to go on exactly in the right place as well, else I'll just cry and cry...

 

[rileytoolworks]

"My preferred method is (if I cant press it in a my vacuum press), to use the dry bonding technique with PVA and a household iron - it works very well indeed."

What does the 'dry bonding technique' involve, and how does it work?

 

[Chris Knight]

Riley,
Basically you pre-glue both veneer and substrate with PVA, then after it has cured, you iron the veneer onto the substrate, (melting the glue in the process. which as a thermoplastic, sets again when cold). There is a FWW article here that explains it.

 

[Calpol]

How do you stop the veneer curling after the glue is applied? Also I'm not a member on that site but I'll have a look for another explanation...

 

[RogerM]

Calpol - PM sent.

 

[woodbloke]

Calpol wrote:

Obviously can't do that at home though!

It's quite possible to do a bit of curved veneering over a former at home using a vacuum bag. The baseboard must be made much smaller to allow the back to draw down over the former. If the original base is used (which reaches to the edges of the bag) then there is a very good chance that the bag will split if used with a large former - Rob

 

[Calpol]

Aye, I can see what you mean, just I don't have a vacuum bag :lol:

Was looking at getting one a while back though, I'm quite a fan of veneering and it'd certainly get plenty use

 

[Chris Knight]

How do you stop the veneer curling after the glue is applied? Also I'm not a member on that site but I'll have a look for another explanation...

Just spray the non-glue side lighty with water.

That Taunton site is worth every penny - join it!

 

[MIGNAL]

Neither the contact adhesive or the iron PVA method are great long term options when it comes to veneering. They might be OK for thin strips but when it comes to larger surfaces there are much better options. Either Caul veneering - which is fine on small pieces providing your set up is good, Hide glue or hammer veneering - very good but takes quite a bit of experience or Vacuum veneering - involves more expense and glues with more open time. Your best option if you haven't the experience with hammer veneering is to use the PVA method, even though it's not the most reliable.

 

[Chris Knight]

I disagree entirely about the suitability of the PVA method in the long term. I have used it for years and found it to be completely reliable in all shapes and sizes, with veneers from 0.7 up to 3mm in thickness on both flat and curved work.

 

[MIGNAL]

It's well known that the PVA method is not as reliable as the others, probably because of the glues susceptibility to creep. I didn't say it would automatically de-laminate after 5 years, I said that it wasn't as reliable as the other methods. That's partly why people go to the trouble and expense of Vacuum veneering. I made extensive enquiries about the various methods when I set up a commercial venture that involved doing a small amount of veneering. Getting it wrong simply wasn't an option. All the advice I got from the people who do it commercially was to avoid the PVA method and invest in a Vacuum press or use the traditional hammer method if I wanted to avoid 'returns'.

 

[woodbloke]

In my view PVA adhesive (I use a D3) for flat work is as good as any other and I use a vacuum bag for pressing. I would use something else though for curved work. I was in a shop recently and was reading the label on some D4 adhesive which claimed to be 'creep free'...not sure if this is the case - Rob

 

[Chris Knight]

(Rob,) D4 refers to the water resistance (D4 is supposed to be waterproof as opposed to water resistant like D3). BS 4071 is the usual standard for creep resistance.

It's true that PVAs have less creep resistance than some other glues - people usually talk about UF glues in this context as they are very cheap, have been around for years and years and perform well in a manufacturing situation with hot presses or RF heating.
Some PVAs claim more creep resistance than others, in general the yellow glues like Titebond claim more creep resistance than the white glues like Evostik Resin W. However, there are plenty of slightly specialised white PVAs that are claimed to be more creep resistant than the usual stuff - I use a Hallmark Fraulo glue for veneering usually.

Polyurethane glues are excellent for laminating but they are very messy and the slipperiness before they grab can be a problem.

I reckon hammer veneering is horrible for curved work with thick or recalcitrant veneers, fine for flat stuff but watch out for shrinkage and splits.

If worried about creep, consider the loads involved - flat surfaces it's gravity only, curved work and its potentially springback and gravity. In most cases both gravity can be discounted as trivial (because of the light weight of the veneer). Springback is potentially a lot more serious and might need to be reduced by pre-bending laminations - certainly pick a glue other than PVA if considered a problem.

Considering the forces involved, veneering a demilune table could hardly be simpler or less demanding on glue type so go with whatever makes you happy.

A bigger force will be wood movement resulting from moisture variations and this will ultimately destroy all glued joints (look at veneer on old furniture to see how 50 or 60 years treats it, there are usually a few failures to be spotted) and whether it's the glue or the wood itself that actually fails is probably immaterial. (As Keynes said - "In the long run we are all dead")