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Laminating veneer with non-UF2/3
Has anyone switched from UF to PVA or other adhesive for laminating wood veneer? Anyone tried contact or PUR adhesives? I would like to hear of firsthand experiences--good or bad. Thanks..
I have done all of the above. The switch from UF to PVA wasn't too bad; a change in press cycle time (longer) and temperature (lower) was required, but the only other thing we changed was to let products pressed with PVA "cure" for a period of time, usually over-night, which wasn't required with UF, you could just let that cool to room temperature and it was ready for further processing. On the plus side, if a panel came out of the press with a blow (using PVA) you could put it back in the press for another cycle and it would reactivate the adhesive and you had a chance of it being okay. That wouldn't happen with UF.
Contact cement is difficult to work with on single-ply veneer. I only used the solvent-based, but even then, as soon as you put it on the veneer, it would start to buckle and wave. It took a great amount of care to get it laminated to the core without bubbles forming, and then putting on a finish was a real crapshoot, the bond often came loose. I would never recommend contact cement for laminating single-ply veneer to a substrate.
PUR works quite well, as long as you have very flat veneer. Any buckle present when you sent the panel through the pinch rollers would "travel" down the length of the face and usually split open as it got to the trailing end. Maple was nearly impossible to press with PUR without splitting. Other species less prone to tension in the veneer worked okay, but you really didn't know for sure until it came out of the pinch rollers. Too much risk and too little reward for me.
My first choice for laminating veneer to substrate would always be UF. It's losing popularity because of the no-added-urea-formaldehyde requirement many end-customers want today, but there is no better, cheaper and more effective way to laminate veneer to substrate.
We made the change from UF to PVA about five years ago and have had a positive experience overall. Much like the previous poster, we have been able to reactivate some panels with minor bubbles. However, the performance of the PVA in extreme humidity conditions has been less than stellar. The UF would hold the veneer in place and the panel would warp. Now, with PVA, we have experienced some veneer checking and delamination due to humidity extremes. Overall, in spaces controlled according to AWI specifications, we have not had any issues. If the expected humidity range is outside of those specifications or will vary significantly within them, PVA just doesn't hold up as well.