Fixing an Uncatalyzed Top Coat

      The finisher forgot to add the catalyst. Can the sticky, uncured top coat be fixed? Maybe ... March 26, 2013

Question
We are using M.L. Campbell Duravar and it is 2k CV. My sprayer applied three coats with care catalyst, but with the final fourth layer he forgot to add care catalyst as needed. After four days it didn't dry. How we can fix it, while not re-finishing it?

Forum Responses
(Finishing Forum)
From contributor F:
What I'm going to say is not what you want to hear. That last coat needs to come off. You could probably do a solvent wash since it's been four days. I'm not sure about Duravar, but Magnamax achieves 80% cure in two days if memory serves me correctly, so I would think that Duravar would be at least as quick.

I donít think that I would start with a fast thinner but maybe a retarder or reducer. Care retarder or C161 or C162. If it's still a little gooey you may be able to lightly scrape or wipe off some of it before the solvent wash. It will of course need to be sanded after the last un-catalyzed coat is removed. Make sure all is dry and recoat.

Keep in mind for future reference that Duravar is 32% solids and applying four coats at 4-5 wet mills will yield 5.1-6.4 dry mills. Both are too much. It needs to be no more than a total of five dry mills. Also, you may receive some responses that tell you that you can double catalyze a new coat and apply and you will be ok - don't!



From contributor R:
Catalyze (standard 10%) and spray another top coat. You may get by with that. Do not spray another coat over the top or you will likely get crawling. As the other poster stated four coats is too much. Generally we do two coats, three on softwoods, and have great build and film properties.


From contributor J:
I know it's too late, but Duravar is a two coat maximum finish. Why the third coat? As others have stated, just try to remove the last un-catalyzed coating and sand enough for the last coat to bite. Next time ask your spray tech to follow instructions!


From contributor D:
It isn't designed to work like that, and it will not work. If it doesn't show failure immediately it will down the road. I imagine at this point you might be able to work off the un-catalyzed coat with a grey Scotch-Brite and mineral spirits (so it isn't too aggressive on the two bottom coats). It will be yucky and messy. Wipe down with thinner before spraying a properly catalyzed coat.


From contributor S:
The workaround in this type of mistake is to shoot on a flow-coat of catalyzed Duravar. The idea is that the catalyzed topcoat will kick the un-catalyzed and start the crosslinking in that undercoat as well. This approach isn't guaranteed to work. Sometimes it does and you can't predict that it won't work. If it works, you'll know it because your topcoat will cure. I speak from experience. I did the same thing when spraying on-site once. The customer was aware, also. I told them. No call back.

Again, the theory is proper. A hot topcoat has the potential to kick an un-catalyzed undercoat. (I would add a tiny amount of MEK to my topcoat to get a better chemical bite other than what solvents are already in Duravar and their lacquer thinner).

Now I'm going to talk about the so-called number of coats of Duravar because that's also where there are many misconceptions. Regardless of how many applications of the material, the total coating weight of the film of finish shouldn't exceed 4-5 dry mils of thickness. That film 4-5 dry mil thickness includes your sealer coat and stain coat and whatever else is sandwiched into your finish. Your most durable finish is with the two coats of Durvarar, sprayed un-thinned. That gives you all the great performance characteristics for which Duravar is known, including its heat resistance (150 plus deg F). If the dry film is too thin, what protection can it offer? If it's too thick then it cracks and fractures (excessive coating weight).

Two continuous films of finish properly adhered by at very least mechanical adhesion (scuffing between coats) gives you the great performance, as I said. What about thinning your material so you can spray it better? I'm all for it. Do it, but scuff between coats to insure adhesion of the applications to each other. Look at it logically - several thinned applications of film adhered to each other versus a couple of thicker applications of film also adhered to each other, where's you greatest strength? The thicker applications of course.

Why? The thinner applications also yield fantastic performance of Duravar as a coating as long as the total coating weight doesn't exceed the 4-5 dry mils of thickness and also as long as you don't starve your substrate for finish. That means in the end make sure you have 4-5 dry mils of finish thickness (do your math) and call it a long day.

What's with the coatings companies? They have to try to push you not to thin their coatings for the purposes of "green". Also, the more applications of the material, the more of an increase in your labor and solvent costs. For purposes of marketing they need to sell you a product that will help you make money and make your overhead smaller. Two coats instead of six coats is a huge savings in time and everything else. What a great product that a production friendly cabinet shop needs in order to survive, quote jobs, and pay their workers. Fact, theory, and marketing hype - read between the lines.



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