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Coating Thickness and Pre-Catalyzed Lacquer Performance
Question
Forum Responses
In your case, if you can start grinding that coating down, then you will be better off in the long run. If not, hope for the best. And if the coating does fail or if your customer complains about its lack of performance, then prepare to strip it off and refinish. This time around, either use plain old lacquer or a coating that enjoys a much better reputation (MLC coatings are fine except for Magnalac, which has a track record with way too many shops for failure). In your case and in the case of many other Magnalac users, the failure of this coating is only the result of operator error. Not enough respect is given to the guidelines spelled out in tech sheets. There's nothing cut in stone that your coating will be doomed. Just be ready.
From the original questioner: Thanks. Do you know how long it takes to see shattering, if it is to happen? Since the piece is still in the shop and it won't be delivered for a couple weeks, I'm willing to take a scraper to it unless you think grinding down with 220 would be fine - I'm a little afraid of marring the stain. Also, after reading all the info on the downsides of pre-cat and Magnalac, I'm wondering if I can topcoat with my old reliable CV. Will this be compatible in the end? From contributor D: There is no timetable for a failed finish. Finishes give up the ghost on their own. Other than that you know that you have exceeded the film thickness limit, there is no way to tell what will happen. Your best shot at avoiding finish failures is to follow the tech sheets to the T. Even then, things happen. Did you thin your Magnalac? Magnalac is anywhere from 17% to 22% solids by volume. How thick were your applied coatings (wet mil thickness)? What about sealer coatings? Your scuff sanding… did you grind away a good portion of coating or did you only create a tooth? Your coating may already be too thick. No, you cannot add conversion varnish on top of a coating which may already be too thick. In general, adding conversion varnish to an existing topcoat from a different system (precat lacquer, in your case) is inviting risks. The first risk right off the bat, assuming that you had some mil thickness to play with, is one where your CV topcoat causes the Magnalac undercoat to wrinkle. Grinding back applied coatings of precat may invite wrinkling. If you sand through a layer and do not use a spot application of vinyl sealer, then your next applied topcoat can work its way under your sand through and cause what's there to wrinkle. If you thinned your coatings enough, then you may not even be at the 4-5 dry mils of cured coating. No problem and no worry.
From the original questioner: Thanks again. I did thin the Magnalac by 25% and sanded pretty thoroughly between coats. So I guess I'll cross my fingers and wait and see. It's also time for me to get a measuring device for mils. From contributor S: Six months to a year is the critical time window for Magnalac cracking. If you get past the year, you've got it made. Problem is, I've never gotten past a year. Why MLC still sells this loser when they have infinitely better products such as MagnaMax readily available is a mystery. From contributor M: Your comment about sanding with 400 between coats caught my eye. I know with Max and Krystal you need to use a more aggressive paper, like 220-320, because the catalyst will not allow it to bite into the previous coat like NC. Not that a manufacturer would ever admit fault, but they could claim "micro polish" between coats, hence the lack of adhesion. But I do not know if Magnalac has the same properties as Magnamax when it comes to melting into the previous coat. Campbell has good product information available on their website. It covers wet/dry mil thickness, as well as recommended steps. Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Have you reviewed the related Knowledge Base areas below? 
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