What is the modern alternative to using Urea Formaldehyde for Bent Laminations ?

**RoyG** · 20th January 2015, 11:50 AM

Greetings,

My next project will be a Circular Dining Table in Queensland Maple. The table has curved rails between the legs. The rails are bent laminations (3 mm thick laminations), built up to approx 25 mm thick, and bent to a curve radius of 540 mm.

I've done a fair bit of research into what glue to use for the bent laminations. Much of what I can find in books and on the web is fairly old information and recommends using Urea Formaldehyde or Resorcinol Glues to end up with a ridgid glue joint and to minimise "spring back" in the bent lamination. It seems that although these glues are still in regular use in industrial environments, it is pretty hard to get hold of them in smaller retail quantities. I suspect that the high toxicity of these glues is one reason that they've disappeared from the retail market.

So, I've started looking at what modern and readily available glues are most suitable.

Lots of people report that they use PVA glues for their bent laminations, and don't have problems with spring-back. So, I did a test bent lamination using some 3 mm thick hoop pine laminates and Titebond Type 3. I left the glue-up in the clamps for 48 hours. The first problem I ran into was that the glue went off too quickly. My test piece only used 300 mm long laminates, and I only just got it clamped up in time before the glue tacked-up. So, when it comes to gluing up laminates that will be roughly 1.2 meters long, Titebond 3 will definitely go off too quickly. I also got about 5 mm of spring back after the test piece had been out of the clamps for about two days. The only good thing to come out of the Titebond 3 test so far has been that the glue lines in the test piece are nearly invisible.

So - what is the best modern glue for Bent Laminations; where spring-back will be a problem, where long pot life is needed, and where it would be desirable (but not essential) to not see an obvious glue line ?

Your thoughts please ?

Regards,

Roy

**Vernonv** · 20th January 2015, 12:07 PM

Epoxy.

**orraloon** · 20th January 2015, 01:01 PM

As said epoxy.
I have made a few archery bows and you cant aford any creep back there. Epoxy is the shure no worry glue for any bent lamination work. It took over from urea type glue about 50 years ago. I use Techniglue and it has a pot life of almost 1 hour. Follow instructions on can. The other contender would be West Systems Epoxy.
I mentioned pot life but better to mix on a flat surface to avoid thermal reaction. Paper plates(not plastic) are good for this.
Regards
John

**mark david** · 20th January 2015, 01:10 PM

Hi you can use pva but it's probably far from ideal as it has too much tack and not enough open time.
I have tried this but there's a lot of spring-back.

Would probably suggest West systems as it has long working time and very little tack initially allowing the laminations to easilly slide over each other,

**elanjacobs** · 20th January 2015, 06:48 PM

Epoxy or polyurethane

**Vernonv** · 22nd January 2015, 09:15 AM

Here is a quick example of a ski I laminated over the last couple of days. It was a layer of 3mm solid timber between 2 x 7mm sheets of ply. Epoxy was Consolidated Coatings 5:1 epoxy (link) mixed with phenolic micro-balloons. Bend was 15 inches over a 22 inch radius.

EDIT: Oh yes ... spring back was under 5mm at the tip of the ski.

20150121_180753.jpg 20150121_180745.jpg 20150121_181521.jpg

**Mr Brush** · 22nd January 2015, 10:26 AM

There are some very good polyurethanes for this application - if you don't mind shipping it from down south, talk to Shawn at Monaro Timbers (Canberra) about this. They have some new polyurethanes which are used for commercial applications; he showed me some completed samples, and it looks very impressive. I think he brings the material(s) in from Germany in bulk, then decants it into smaller containers (e.g. 1 litre) for sale.

As for epoxies, I've used Techniglue and West System but prefer West System for bent laminations. It is thin enough to be rolled on with a foam roller (speed is of the essence !), and there are a couple of different hardeners available. You can buy maybe 1 litre of resin, then smaller quantities of the different hardeners to suit the application. They do have a very slow cure hardener which is ideal for bent laminating (I forget the part number). Techniglue also have a slow curing hardener, but only available in quite a large tin - it will be long out of date before you use it all up.....

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