Whether to Scuff-Sand Between Coats of Pre-Cat
Scuff coats improve adhesion when using formulas that may cure before the next coat is applied. December 23, 2014
Question
I'm trying to convince the boss that it's alright to spray back-to-back coats of Magnamax without sanding, as long as it's within a short period. Please give me (or him, rather) your thoughts.
Forum Responses
(Finishing Forum)
From contributor K:
Sure, it’s alright to spray lacquer on top of semi dried lacquer without scuffing, but you get a better finish if you scuff between coats - both in adhesion and appearance. Lacquer will burn into the previous layer of lacquer and create a chemical bond, but it won’t get rid of any imperfection such as dust like scuffing between coats would.
From contributor M:
He's talking about pre-cat lacquer, not straight nitro or CAB. I've sprayed a lot of Magnamax. It kicks over and reacts pretty hard. I wouldn't trust it unless the re-coating was done in a couple (under five) minutes of the previous coat. Even then, you're flirting with risk. One small parts, here and there, sure. On whole kitchens, I would not. Pre-cat lacquer crosslinks as it cures and, according to the manufacturers, it does not burn in. Straight nitro and CAB does. Not precat generally speaking.
From contributor F:
I use Sherwin Williams pre-cat. I sand after the first sealer coat with an abrasive pad and add multiple coats after that with no sanding in between. I do however wipe down with a tack cloth before each coat. I think if you keep your pieces clean, there is not much difference in quality than if you sanded every coat.
From contributor J:
It depends on the pre-cat. Some don't have much more solvent resistance than Nitro while others are almost as good as CV. Not all pre-cat's are created equal.
From Contributor D:
For Magnamax you'd better scuff in a scratch pattern. If your coating is still tacky then you can get away without scuffing. The tackiness of the coating is an indication that you'll get a chemical bite. You should note that MLC lacquer thinners are formulated to be weak in terms of solvency. This is part of the design so that the operator doesn't have to worry about introducing a recoat window into his spraying practices. For this reason alone scuff sanding to insure proper intercoat adhesion is your best practice - always.
