Troubleshooting Veneer Checking

      A veneer jobs shows checking after nine months in service. What could be the cause? July 12, 2013

Question
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?

Forum Responses
(Veneer Forum)
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:

Veneer Checking



From contributor C:
The use of NAF board adds to the movement. In essence, the board is dust held together with white glue. Using the 'evil' urea formaldehyde based board produced a board with actual hardened resin in it and it was a lot more stable. If your customer wants you to replace the panels, do them using a wood crossband and you will have better results. Also, were these panels hot pressed? If not, that is a contributing factor as you need to drive the water out of the panels quickly before it penetrates too much. It used to be called snapping the glue line.

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.



From the original questioner:
I agree with what everyone is suggesting and they all have some form of validity and practical applications per each unique situation. However, here is why I can't do what Contributor C suggests regarding the glue and substrate. Ninety percent of the projects we do these days are LEED jobs, and this one happens to fall within that category. All substrate used in the manufacturing of wood/p-lam panels cannot have any added urea formaldehyde, that eliminates standard particle board and standard MDF. The glue I must use also cannot have any added urea formaldehyde or should I say it can only have so many parts per million of formaldehyde in it, therefore eliminating the evil urea.

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.



From contributor T:
The important thing is after the hot press the veneered board needs to be slowly cooled and coated with PU sealer as soon as possible. Use two-four coats. When applying dye stain it can be sanded for good stain penetration.



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