What are the pluses/minuses of using yellow glue for veneering? Are you better off using glues like Unibond and why? What are the trade-offs?—Michael Brown
Peter Breu replies: Yellow glue can be used by allowing it to dry and then reactivating it with heat (an iron) which is good for smaller projects or uneven surfaces, but there is always the worry of creep. Unibond is much better as it will not creep, but it requires a veneer press (either manual or vacuum). If at all possible I would use the Unibond as it has a long open time and provides a perfect bond.
Jeffery Cooper replies: Yellow glue privides a perfectly strong bond for veneers. I use Unibond for larger surfaces where I need more time spreading it. A risk with Unibond is that with veneers thinner than they used to be, you have to be careful with sanding or the darker color can show through lighter woods.
Here is one suggestion for either. Use a tooth trowel to spread the glue instead of a roller. It’s easy to tell exactly what coverage you have, and clean up is easy.
Owain Harris replies: I use both PVA (yellow) glues and urea formaldehyde (Unibond) glues in my veneer work and they both have their place.
PVA glue is a great all around choice for lots of veneering and with it’s quick set time, parts can be removed from the press usually within an hour. I will typically use the Type II cross-linking version as it is a little more rigid and is waterproof. This is nice when your glue line is so close to the surface. The disadvantages are a short open working time and a flexible joint that will spring back if used to laminate curved parts.
If I am doing larger more complicated lay-ups or bent laminations, then I will definitely reach for the urea formaldehyde. The long working time reduces the stress of trying to get a large piece covered before the glue starts to kick off. And the rigid joint will almost completely eliminate the chance of spring-back in bent laminations. Another great thing about Unibond is the ability to alter the consistency of the mix by adding a blocker, which will reduce the likelihood of bleed through when working with open grained woods. Disadvantages are the mess, the mixing and the cure time. Parts glued up with Unibond will have to stay in the press for at least five hours and I will usually leave curved parts overnight to be safe.