Slow Drying and Curing in Refinish Jobs

Troubleshooting the cause of splotchy curing, where some areas in a refinished piece don't cure or dry for a long time.September 3, 2011

We spray magnamax thinned down with fast thinner. From time to time we notice that some areas don't dry and cure. We’re using different woods and different types of ML Campbell lacquers. It seems to be something in the prep or wood. A light mist coat over the areas seems to dry it out. Just wondering if anybody ever came across this or has any ideas as to what causes it. We are a refinishing company only. Out process is:

Strip and dip.
Dry for a few days.
Sand to 320.
Seal/stain and three coats on top of MagnaMax.

Forum Responses
(Finishing Forum)
From contributor G:
Why are you using fast thinner and is it MLC thinner? You should be using standard thinner. The fast thinner is now the same as the economy thinner which is really used for cleaning because it is inexpensive.

From contributor P:

I would look into the following:

- Try a slower reducing solvent to allow the matting agent to flow out more evenly before the coating starts to kick.

- Ensure that you are over lapping 50% on each pass of the spray gun to get even coverage.

- Allow the coating to dry longer between coats to ensure all the tail solvents are out before entrapping them with a subsequent coat.

From contributor C:
I would only sand to 180 grit. 320 can cause polishing of the wood, sealing the pores.

From contributor G:
I didn't even catch the 320 grit. Yes, in between coats 320 is fine. But on raw wood MLC recommends not going above 150.

From contributor K:
Take note of the wood type and of the areas that stay wet. One bet would be that the anti-evaporation stearates in the stripper have made their way into some softer or spongier areas that the rinse and neutralize do not wash out. Sort of like washing peanut butter out of a sponge. These bloom up into the lacquer and keep it from curing. Sometimes a few days dry is not enough. On really soft spots, it may never dry fully.

From contributor A:
Contributor K is right about the cause. To fix this problem, simply wipe a few times with naphtha on a dampened rag, works like a charm.