Troubleshooting Veneer Cracking After Finish Application
A case of veneer checking leads to an extended discussion of adhesive choice for veneer layups. March 30, 2008
Question
I'm having trouble with rosewood veneer cracking. Sealed with Becker Care-seal, one light coat, let dry for a few minutes and went back over with a heavier box coat. Let it sit overnight, scuffed with 320, and noticed a few hairline checks in the veneer, then sprayed a good box coat with Fiesta 60. As soon as I applied the Fiesta, I noticed that the cracks really took off, running in some spots the entire length of the piece of rosewood. Is it possible that there is a problem with the finish, or do you think the veneer is defective?
Forum Responses
(Finishing Forum)
From contributor C:
Sounds like the veneer, but spray a new sample with a different clear finish that you use and see if it is doing the same thing.
From contributor V:
The problem is most likely the bond between the veneer and the substrate. Bad batch of glue, improperly mixed, inferior substrate, substrate sanded too much before veneering.
From the original questioner:
I am in the process of spraying another piece this morning with a different product. I think it is the veneer also. I sent samples back to the manufacturer and of course he is saying it is the finish. What a mess... Have the whole kitchen in the finish room with the sealer applied and it is all junk.
From contributor J:
How was the veneer applied? What glue was used, etc? Using a glue that allows the veneer to move (contact adhesive) can cause finish cracking when the veneer moves more than the finish can flex. Contact is for laminate, not veneer.
From the original questioner:
I bought the rosewood laid up on MDF from a large mill in Canada.
From contributor O:
I had the same problem with a job I did for a customer. It was a Tetra negrozene finish, (almost painted black) on rift white oak. I finished the job and it was fine. He left it in a truck for a few days in the middle of winter with 20 degree temperatures, then drove it to the job and put it in a 75 degree apartment in the sun. The whole job checked where the veneer was. He blamed it on me, even though the oak was glued on to white melamine using contact cement.
From contributor C:
You need to use cold or hot press glues for first class work that won't have these issues. Cold or hot press on MDF should be fine; oak veneer over melamine with contact is a no-no! Rosewood should be laid up with a glue that is made to adhere to oily woods such as teak or Brazilian rosewood. Smith's rosewood/teak glue would be an example. But if someone else is laying it up and they don't use the proper glue/adhesive, checking, cracking, and other things can happen. Yes, the company who does this should know, and maybe they do, but it should still be specified by you! That way there will be no wondering about it. Will it cost more per sheet? Well, how much money have you lost so far taking care of the problem? How far has it put your schedule behind on other jobs you had in progress? How much more in labor and overhead? The extra cost, in light of these things, is nil.
From the original questioner:
So you are saying that I should have specified on my po that the supplier should use a specific glue? I have never heard of such a thing. And why are you suggesting that I tried to save any money by using this company? I had four companies price it and gave it to the one that I have used in the past. He was the second highest price.
From contributor J:
Contributor C is right; not all companies are going to use the right glue. I don't think he was implying that you were being cheap, but maybe that they were. Just because they are not the cheapest source, does not mean they are doing right. You have the right as a customer to know how they lay up your panels, and if they are not willing or capable of doing it the right way, you need to look elsewhere. I agree it seems silly that you should have to specify what is their business to know, but it you want quality materials, it pays to be a demanding customer.
From contributor C:
I was the buyer/specifier/finish supervisor for OSF America back in the 90's, and yes, we were using
water base stains when I first started there and they were having all kinds of troubles with seams opening and curling, etc. So not only did I take over the role of veneer purchaser, but also of specifier to those companies who laid up the veneers. What was needed was a waterproof glue/adhesive on MDF. Yes, you have the right to specify what glue you want used as well as the thickness of veneer you want (if available) and type of substrate. You can even specify the manufacturer of each of those you want them to use and provide them with contact info or anything else.
Now, although you can do this, many will not do it if it is a short run - meaning 1 or 2 sheets of goods, and of course the bigger the order, the more they will accommodate you. In my case I was ordering 5 to 8 flitches a year of block mottle makore to be laid up as well as many other woods such as purpleheart, ebonies, cherry, and walnut, etc. For million dollar orders they bent over backward for us. But I have also ordered 1 or 2 custom sheets in different small concerns where the places I dealt with understood my needs, and as long as I was willing to pay their price, I had no problems there either.
From contributor V:
A mill that does regular runs of pressing is going to use a U/F glue. Even a PVA that is approved for hot pressing is not going to peel away easily. We did extensive failure testing when the shop I worked for switched to a PVA for all hot pressing, and the problems we had were due to poor surface on the substrate or an improperly mixed U/F. Occasionally the surface of the MDF was extremely smooth, and the glue would not penetrate sufficiently.
U/F glues are usually a pre-cat powder that is mixed with water, or a resin mixed with a powder, with water added to increase open time. In either case, if there is too much water added, you get a poor bond.
From contributor C:
You're absolutely correct. Yes, your UFs and PVAs are used extensively, along with resorcinol in the boat or marine industry. Is the rosewood veneer you're using Brazilian rosewood or one of the others? Brazilian rosewood has the most oil of all the rosewoods and like teak needs an adhesive system that will readily adhere to both it and the chosen substrate. If it's B. rosewood, the wood itself should be treated with a solution of 5% phosphoric acid allowing the albuminous matter to float to the surface, and then it should be wiped away with clean rags soaked with 95% ethanol. Left to dry and then applied to the substrate. Do you have to do this? No, but you will find the results to be superior when you do. This also holds true for finishing purposes as well before applying any coatings to the rosewood. For untreated wood/veneer, I still suggest you use an epoxy glue that is formulated and proven for use on oily woods. Overkill? I'd rather wear a belt and suspenders than have my pants fall down in front of my clients.
