Troubleshooting Peeling Conversion Varnish

      Looking for the causes of peeling second coat on a conversion varnish finish. October 25, 2006

We have had two jobs lately with which we had a problem with MLC's CV200 (a low-stink version of Krystal). In both cases, we stained the product with MLC stains and allowed for the proper cure time (actually about 4 times the recommended cure time). The first coat went on fine. Scuff sanded smooth. Second coat, we got this peeling (like your back after being out in the boat all day when you forgot the sunscreen). The peeling starts at the corners/edges of panels or shelf nosings, but only in one or two places (usually a 2-3 inch long area). The rest of the nosing and entire cabinet or shelf is fine.

It really looks like the second coat of CV200 is dissolving and lifting the first coat. But only near the edges, as if it's getting up under it where I may have sanded completely through the first coat. But why am I having this problem only on this product? Never happened before with Duravar, Krystal, or Magnamax. Not even a hint of this.

We contacted the rep and we have yet to get an answer we believe. They claimed that the catalyst sometimes settles out of solution, leaving a less-durable coat. This can't be the case, because the first coat we lay down is a freshly mixed batch. Anyone else have problems with CV200? It is a fantastic product when it's behaving, which is the vast majority of the time. We just can't have this peeling thing happen on every other job; it's a pain to fix (you have to sand to raw wood and restain/recoat).

Forum Responses
(Finishing Forum)
From contributor J:
I can't answer your post since I have not used that particular product. But I have started using Target's CV and find it very easy to work with and a very nice finish. I have not had any problems with it.

From contributor R:
It would have to be that the first coat is improperly catalyzed or the first coat has adhesion issues with the stain. Go to Radio Shack and buy a 100 power battery microscope and look closely at the failure. If the finish is peeling off and the stain is left clean with nothing sticking to it, you have an adhesion problem.

From contributor D:
Cellophaning/peeling is usually a signal of problems with intercoat adhesion. What grit are you scuffing with? Back at the stain level, are you doing a clean wipe or are you leaving an accumulation? You may need to scuff with a heavier grit to create a better scratch pattern. Usually, between coats, 320 is the proper grit. You might want to try 280 grit and see if there aren't sand scratches which telegraph through the topcoat.

"Settle out of solution"? Maybe I missed something, but settling is something that happens with suspensions. Solutions stay dissolved until stuff evaporates, then you have precipitates. When adding catalyst, the mixture has to be thoroughly stirred.

Instead of asking your rep, you want to get the MLC technical support involved. You need the input from the formulator(s), not a salesman. ML Campbell makes great products. But has there ever been an instance where in a crunch, they have had to stand behind their products? According to them, it's always, always operator error (and this is usually the case regardless of the manufacturer, but there does exist in this world bad batches and bad formulations).

From the original questioner:
We had thought about it being a stain-topcoat adhesion problem. We will investigate that a little further. We scuff with 320. Stain - we are wiping off all we can, not trying to muddy the grain. The "settle out of solution" stuff the rep said sounds like hockey to me, too. Catalyst is always well mixed, we're quite careful with it. We have to re-stir it every few minutes that it sits still or the flatting agent settles out (this isn't our problem, however, this creates an altogether uglier problem).

From contributor S:
I remember some literature for the CV2000 said be careful not to sand through on edges and corners, as burn through to the base coat or film failure can occur.

From contributor C:
I like the phrase "low stink" version of Krystal... that's exactly what it is - it has a different solvent package, and also is lower in viscosity. If the second coat is lifting off the first, then you have to troubleshoot intercoat adhesion, like maybe scuff sanding with 220 grit instead of 320 grit paper, or possibly some kind of burning through of the seal coat when scuff sanding. If the second coat is lifting through the first down to the stain, then you have to troubleshoot post stain, pre seal coating problems, like what grit you are sanding with, is the stain getting wiped off all the way to the outside edge of your shelves or panels, etc. Yeah, it's a great product. Hopefully this is the only bad run you'll have with it.

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