Loader Update Touching Up PPG MAE Question

I sprayed the MP170 on about half of the loader parts yesterday afternoon then topcoated these parts with MAE on this afternoon. Did have a few small runs while developing my "technique", if you could call it that, but overall I am pleased with the results.

Question: Some nooks and crannies were impossible to cover without moving the parts. The MP 170 primer dryed so quickly this was easily accomplished but with the MAE I could not touch the parts to reposition them which left some areas with little or no MAE topcoat. Will it be alright to overlap the areas I painted this afternoon tomorrow afternoon (i.e. 24 hours later) after I reposition the parts to be able to spray these hard reach reach areas?

Rod

If you didn't use hardener in the MAE, I'd approach your situation with some caution. The potential problem with recoating some unhardened enamels is lifting and wrinkling of the film when more paint is applied after the initial dry period. The recoating of unhardened MAE is not addressed in the tech sheet. I have asked PPG about that in the past. You can read my question and PPG's reply in this previous post. Since I don't use MAE, I have never tried to recoat it like you would like to do. I simply don't know from any experience with it what you will run into. The PPG response is not promising. You can only try it and see what happens. CNKS is correct on the overspray. You should expect to have a loss-of-gloss around the overlap area because the new paint overspray will not "melt in" to a previous paint film that has dried. Always try to plan out a progress sequence that will permit you to keep a wet edge and complete the task before actually spraying anything. Usually you attack the hard to get at or less noticeable areas first.

Rod

I wouldn't push the flash time too hard or you will have trouble with the melting in of overspray. How long you can safely go beyond the stated 10 min (@70°F) is not defined. I don't think I'd want to push it a lot - but that's only a guess. That's for the overspray issue where you are doing a partial recoat or coming back to a point where you started earlier with the same coat. On the other hand, if you are talking about a complete reshoot where you are reshooting the entire part at a later time, I think it's a different case. In that instance, the concern is not the blending or melting in of overspray but rather the quality of chemical bonding of the new coat to the previous one(s). In the case of MTK which must be catalyzed, there is no concern with lifting after drying and the matter becomes one of bonding. MTK can be cleared up to one week per the MC161 tech sheet. I have never let it go that long and prefer to clear as soon as possible after the stated 4-6 hrs (MTK tech sheet). In clearing over decals I have deferred the clearing for two days - no scuffing. I'll assume that bonding of clear is essentially the same as bonding of more color (they use the same hardeners) and guess that you could safely recoat up to one week without scuffing. I once had to recoat MTK color because of a disaster (long story) during the second coat. I let it dry overnight, scuffed with Scotch-Brite and reshot two coats over the whole part. No problem. The reason I scuffed was because the part was relatively small and it was easy to do - an extra precaution and likely unnecessary in that time period.

I don't think there is a specific answer to your question and it depends greatly on the exact product and hardener involved. For example, the maximum time for clearing of hardened MAE is only 24 hours, not one week like the MTK. If I were to recoat hardened MAE, I'd do it within the 24 hours or plan on scuffing it. When in doubt, be conservative if possible.

Rod

Rod