About a year ago our company did a large panel project with qtr. fiddleback eucalyptus. The panels have been installed and on the walls for about nine months and now are starting to show signs of checking. They were laid up on medite substrate with a PVA glue and finished with catalyzed lacquer. At the time some of the veneer was buckled and we did experience some problems splicing it together, however we did manage to get it to stay together and press flat with no de-lam or checking.
Has anyone ever experienced this type of problem and managed to figure out the cause? Would relaxing the veneer with a veneer softener prior to clipping, spliceing, and pressing have eliminated this delayed checking problem? I've pressed eucalyptus in the past and never had a problem like this. Is the core, glue, or environment in which the panels are installed a possible culprit?
From contributor V:
The short answers to your questions at the end of your post are yes, yes, and yes. Moisture issues are the culprit in veneer checking issues. If the core is a higher moisture content then the veneer it will create issues. Using PVA glue that has a high water content also can add to this. The thermoplastic nature of a PVA can also create issues. Also PVA glues are an evaporative cure adhesive and the moisture will travel through the line of least resistance which is usually the veneer. If you flood the finish the solvents in the finish can cause checking. If the veneer was to dry this can also lead to checking with the reintroduction of moisture into the veneer. Veneer is like a sponge - it picks up and loses moisture constantly even with a finish on it.
Here is a link to an excellent Knowledge Base article about veneer checking:
We do a lot of 5-ply crotch mahogany for a manufacturer of grand pianos and we make our own basswood lumber core with 1/20" poplar cross bands. We do use a UF glue on the faces and we have no issues with checking. The faces are treated and flattened prior to pressing.
Has anyone who has worked with Eucalyptus (figured) had to treat it with glycol in order to keep it from checking? I'm not interested in burls or crotches. I understand they need to be treated because of the interlocking grain they have. I have treated more than my share of crotches and burls. Crossbanding will eliminate expansion and contraction in both the substrate and face veneer to some degree, however I do not have the luxury of time on my side in order to do that. I do realize and I fully understand that there is a process that must be followed and certain guidelines that must be adhered to in the manufacturing of wood panels. I'm just trying at this point to figure out what I did wrong by process of elimination, starting with the relaxing or not relaxing of the veneer.
I just replaced a wall with the same Eucalyptus but this time I treated the veneer with gf-20. My moisture content in the veneer was 9% after I treated it and had to go back and hotpress it (it was 8% before I treated it) and my medite was 11%. My pva is 24% solids and my glue line is 6mils. I hot pressed the panels for 80 seconds at 200 degrees F and so far I do not have any checks. I didn't have any checks in the last panels I produced nine months ago so I guess only time will tell.