Gary, here's a couple of ways that usually work. Slainte.
Flattening veneer.
Mix Together-
2 parts PVA glue
3 parts water
1 part glycerin
1 part denatured alcohol- yes, it can be purchased in the UK. We don’t have to buy meths with the blue dye, but that can be used too.
Mix all components together thoroughly and apply to both sides of the veneer liberally.
Let soak for 5 minutes.
Place veneer between thin mesh plastic on both sides and add 2-3 layers of newspaper on top of the mesh. Fibreglass mesh works well as a separator to prevent the glue sticking the paper to the veneer. Add more newspaper, mesh, veneer, etc., stacking as high as you like.
Place this "sandwich" in a vacuum press with a caul on top (1/4" minimum.) and apply full pressure. If you don’t have a vac bag you can put chipboard top and bottom and weigh it all down with anything heavy—sandbags are one option for instance.
Change the newspaper 2-3 times the first day and leave under pressure overnight.
On the second day remove the sandwich from the press and take away the screen, it is no longer needed, as the veneer will not stick to the newspaper anymore, but you can put a layer of plastic down instead if you want.
Change the newspaper 2-3 times on this second day but do not put the sandwich in the press, just place weight on top of the caul to hold the stack down. It’s easy to think this second day is unnecessary since the veneer will be fairly dry but it is not dry enough to press. This extra day is important for good final results.
On the third day the veneer is ready to use. if you do not use it immediately the veneer will stay flat for months provided a board is placed on top of the veneer stack, and light pressure is applied. Newspaper between the veneer is unnecessary at this point.
This is also a good way to flatten veneers for storage. The glue added to the solution will keep the veneers flat for a long time.
If you have a heated press, either hydraulic or vacuum type the whole job can be foreshortened to about two hours to four or six hours.
Flattening veneer for immediate use.
For a fairly quick veneer flattening job start by mixing an approximate 1:8 proportion of glycerin and water.
Spray the mixture on both sides of the veneer with a plant mister and wait for a few minutes to let it soak in. Then place individual sheets of veneer between double sheets of newsprint and weight them down or press them between waxed or polished chipboard cauls. Change the paper every 24 hours.
The veneer should be flat, soft and ready to glue up in a day or two if you're using PVA, hide glue, or other water based glue. If you're using epoxy or something that might not bond if there is moisture in the veneer, keep doing the newspaper routine until the veneer is down to the target MC.
I've heard other people suggest adding a little hide glue to the glycerin solution, but I haven’t tried it so I don’t know if it helps.
