Troubleshooting Rough-Textured Pre-Cat

      It's important to stir it... September 26, 2006

Question
The past couple of paint grade jobs we've done we've had some problems with Magnaclaw. No matter how I sand this stuff, with anything from 180-320 grit, there is a rough texture visible once I spray topcoat (Magnamax). I know for sure the problem is the primer, as I test sprayed a piece of UV finished plywood and the Magnamax laid down glassy-smooth. The rough texture is not unlike what melamine feels like. I get this on every sheet good: MDF, plywood, hardwood. This problem has happened with the past two 5 gallon cans we've had, but I don't know necessarily that I got two cans of bad primer. I just don't know what's up.

Here's our setup and order we have used for nearly two years and it's worked great:
Titan airless (non-air assist), using a 310 tip.
Spraying the primer 4-7 wet mils, particularly on MDF.
Two primer coats, sanding back hard to fill the grain.
One or two topcoats of Magnamax (one being the norm - this has produced good results in the past but not now).

It just seems like the Magnaclaw just doesn't act like it once did. Is it the heat? Our shop stays in the mid 80's.The only way I have been able to overcome it is to sand the hiney out of the first topcoat and spray a heavy-handed second topcoat.

Forum Responses
(Finishing Forum)
From contributor A:
It sounds like orange peel - material not flowing out because the coat was too thin or it dried too quickly (summer heat). Have you tried retarder?



From the original questioner:
I suppose it could be orange peel, but it's a good bit finer than orange peel. I will try some flow enhancer #2 (the retarder we have good results with). I had forgotten about that possibility. What is weird is that no matter how hard we sanded the primer (with 180 grit and a random orbit, followed by 220 and 320), we still had the freak texture. How could it stay around after that?


From contributor B:
What do you do to shake, stir or mix up your Magnaclaw? If you are not using a commercial shaker to shear the pigments into suspension then the concentration of too much suspended pigment could be the problem. When pigmented coatings are properly mixed then you do not have too much pigment, as each particle all gets properly wetted (surrounded and suspended by coating resin). But if you have too much pigment then you get a rough finish because there is not enough coating to surround each particle and wet it out and make it part of a smooth continuous film.

The other side of the coin is when pigments settle and clump at the bottoms of containers. You want an even dispersion, and even suspension of pigments. Proper shaking/stirring (only possible with machinery) is what suspensions need.



From the original questioner:
I stir the 5's with a drill operated paint stirrer. I chuck it up in my Makita 14.4 and mix the stuff at 1700 rpm. I'd think that would be sufficient. Thanks for the advice on that though. Magnaclaw does settle out a good bit if it sits for a couple of weeks without use.



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