Thread: PVA glue TEST

Billy,

First you need to determine what you are testing for. Many glues will successfully bond wood and veneer to MDF, but not all are suitable for all applications and service conditions.

For thin veneers I use my normal cross-linked PVA glue. I apply a thin layer of glue to both surfaces, let them dry, and then join them with an iron (steam turned off). To test the join I glued another piece of MDF (so I had MDF either side of the veneer) and tried to pull the layers apart. I could not. The join worked.

I once tested a home-made polystyrene glue by bonding two pieces of softwood together, screwing in a hook with a heavy thread to either side. Steel wire rope was used to connect one hook to a rafter. The other hook was connected to a 240 litre wheelie bin the same way, so the bin was suspended about 100mm off the floor. Then I started filling the bin with water to see when the joint would fail. It didn't. The wood split before the glue line failed, but the bin was nearly full of water, so the joint survived about 200kg of weight.

When you glue ply or thicker veneers to MDF, the PVA glue still works well, but it needs very good clamping to get even pressure across the entire surface. Often, the quality of the clamping is more important than the glue chosen. When these types of joint fail it is quite likely that poor clamping is the problem, rather than the glue.

Finally, you need to determine what kind of stresses the joint will be subjected to in service, and then design a test that mimics that service condition. For example, do you want to test for failure in tension or shear?

I can't answer the question directly, but many years ago when I was a picture framer I decided to test various brands of PVA with a
very simple, uncomplicated and very unscientific method.
I cut a few mitres, joined them together with no mechanical fastening. After a couple of days I just pulled them apart with my hands....
And the winner was by a country mile... watered down Boncrete.
Easily the cheapest and strongest.
For my purposes I watered it down 2/3 Boncrete and 1/3 water but it could have been thinner on occasions because I would just throw water
in it till it was like milk.

GS. A place my FIL used to work used nothing but bondcrete. They'd use empty dishwashing liquid bottles and fill them from a drum of it.
Cheers,
Jim