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CNKS
06-26-2006 18:39:49
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Re: question re:epoxy primer and sandable primer in reply to DAN9-Midwest, 06-26-2006 16:41:52
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Some dealers are good, some bad, some have their own ideas, which are not always correct. If you use PPG products (DuPont and Sherwin Williams, etc make equivalent products, I use PPG because the dealer is conveniently located), ask for MP170, MP175 catalyst, MP181 primer surfacer, and MAE Acrylic enamel. These are all in the PPG Omni line. As to your other questions. The MP 170 epoxy I mentioned for all practical purposes is not sandable. You CAN sand it, but it does not sand easily and it is very easy to go to bare metal. It does not do any filling, it is applied for two reasons, it adheres very well to sanded (180 grit or coarser according to the spec sheet) bare metal, and it gives excellent adhesion to the next product, be that primer surfacer or topcoat. It does have a 3 day window at 70 degrees in which something must be applied over it. Or you need to scuff it and give it another coat -- if you don't the overlying paint will not bond adequately to it. If your sanded old finish is in good shape, and there is no rust underneath (there almost always is) you can use it as a sealer over the old finish, then use 181 or topcoat. Since it is non sandable, there must be a chemical bond between it an the paint over it, thus the window. MP 181 is known as a primer surfacer. It can be used to fill up to 80 grit sanding scratches -- try to have less than that -- and very small depressions. Since I have supplied air, I have no need for 181, but use the urethane surfacer MP 182. Neither 181 or 182 should be used over bare metal, MP 170 will adhere much better. Both 181 and 182 have good build and sand very easily. As mentioned previously on this forum, lacquer surfacers such as MP 181 can bridge sanding scratches, and later sink into them, sometimes after the topcoat is applied. That's why you should minimize your sanding scratches. Both 181 and 182 will fill 80 grit scratches, but the 181 "may" not last on such scratches, I can't say because of no experience. So keep your scratches to a minimum. The 181 or 182 is usually sanded with 400 grit before topcoating. Although the spec sheet says it can be sanded after a couple of hours, it is probably best to let it dry overnight. You can put on 2 or 3 coats, letting it flash for 10-15 minutes between coats then let it set. You will be wet sanding, unless you have a good air sander and the correct paper. When you wet sand squeege or wipe the stuff off, and you can see if you missed anything. Block sand it and see if you are satisfied with it. You may find some dents or depressions you missed or did not know were there. The shallow ones can be filled with a single stage putty, the more obvious ones need body filler, or at the least a 2-part glazing or finishing putty. If you sand these places to bare metal, you should spot in more 170, then apply 181 and sand smooth again with 400. My dealer is a little high on cost, according to what others have said. I pay about $62/ gallon for 170, 12.50 for catalyst (2 quarts/gallon. MP 182 is about $50-$55 a gallon, MP 181 should be similar. Since you only use the 181 on the sheet metal, you won't need a gallon, I don't know if it comes in smaller quantities. You can paint outside, that is not an option for me because of our never-ceasing wind. The link is for nearly all PPG products, it is alphabetical, drop down to the M's and you will find your products.
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Rod