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I'm not sure what you mean by "scaling". Perhaps just an uneven surface?. Any rust scaling present should have been removed by the sandblasting. There could be an uneven surface left though and it all depends on how uneven it is as to whether a surfacer can reasonably be anticipated to smooth it out - if that is indeed what it is. Any chance of posting a close up picture? Surfacers are quite limited in their ability to fill pits and smooth out uneven areas, despite any reference to "high build". For example, a typical surfacer build per coat is usually 1.5-2 mils. Even K-38, PPG's premium surfacer and promoted as "high build" only claims 2.5 mils per coat. They are really for filling minor sandscratches and such and are usually applied using 2-4 coats. In retrospect, that fender of mine should have had the polyester putty applied all over it. It took nine coats of surfacer to take care of the more minor pits outside the area shown where I had used the putty. I simply underestimated the depth of the remaining pits. The spray version of polyester filler, PPG OMNI MX-241 for example, claims a film build of 2-3 mils per coat with 2-3 coats recommended. If your pits or irregularities are deeper than about 8-10 mils, I think you would be expecting too much from a surfacer and need something more like the spreadable polyester to be applied first. If not, then a surfacer could do the trick, especially if you are prepared to apply a good number of coats (not all at once though). I would keep the application to no more than 4 coats at a time before drying and sanding. The tech sheet for the NASON epoxy is very unclear as to recoat periods. Not knowing and never having used that product myself, I'd give the surface a good scuffing before applying a surfacer on top of it. If I were to apply the polyester finishing putty, I would do more than just scuff. My tendency in that case would be to get a good scratch with say 80 grit paper and then apply the putty. After sanding the putty, I'd apply another coat or two of the epoxy and follow up with a surfacer within 24 hours. Regarding a surfacer, you should be aware that many such products contain isocyanates in any required hardener/activator/catalyst, as B--- indicates. If you do not have fresh air breathing equipment, your choices are therefore limited in available surfacer products. They would be the lacquer-based acrylic surfacers such as PPG's OMNI MP-181 or DuPont's 131S. I see that NASON also has an acrylic surfacer that could be used but I have never used that. There is also the possibility of a premium non-iso 2K surfacer (PPG's NCP-250) if you are willing to pay significantly more money for it. I don't have a price for that but perhaps someone who does can jump in with an of-the-street price to give you an idea. I can assure you that it's not cheap. Rod
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Rod