CNKS, Rod, primer on, got a question...

My main question is that there is some old original orange IH primer that I couldnt get off, showing through the MP. Not much just a few places her and there. Is it ok to topcoat over it? I tried hitting it again with the MP but it still wont cover it. What do you think is going on here? I rubed it down prior to painting with PPG cleaner.

Thank You,

scott

Never made it to Baltimore this morning and might try to topcoat today.

I can"t say for sure that your experience with some of the red color showing through is the same as what I"ve experienced. However, I have seen the same thing when I shot 170 over areas of Farmall red that I felt too ridgidly held to try to remove, after wire brushing and sanding. What I believe is happening is that the solvent in the 170 is solubilizing some of the old red paint and it is simply dissolving and bleeding into the new coat. I"ve found if you go back after the first coat of 170 dries and recoat a time or two more, it eventually covers it. Does that mean you aren"t getting a good bond onto the metal with the 170? I assume if wire brushing wont remove the old red paint it is held pretty firmly, and the 170 is going to seal it. Just because solvent can dissolve some of the old paint"s surface doesn"t mean that the paint isn"t still strongly bonded to the steel below. Once the epoxy dries, I don"t think there will be any further bleeding that would affect the MTK coat when it is applied. These guys know alot more than I do - this is just what I"ve seen.

Paul

I really can't comment on the quantity used since I do things piecemeal at different times and have a much higher wastage than normal. It does sound like you are not getting it on heavy enough if you can see though any of it. The 170 covers very well and should completely cover with a single coat. I always use two anyway, but the tech sheet calls for only one. I think that if you are applying it with a normal 50% overlap and you can still see through to the underlying surface then you are not applying it heavy enough or wet enough - perhaps caused by a pass travel speed that is too fast for the rate of paint flow that you are getting from your gun. Is it OK to topcoat over an epoxy that is too thin? Probably - but why not just shoot another coat of the epoxy and get it covered better? You say you hit it again and it still didn't cover. That also suggests that you are applying it too thin (not wet enough). If you have it too thin over bare metal areas, you simply won't get the best corrosion protection from it.

The reason I use two coats of the 170 is a voluntary carryover from my prior use of PPG's premium epoxy - DP (now DPLF). That epoxy calls for two coats for best corrosion protection unless an etch primer preceeds it. I don't use etch primers so I always used two coats of DP. The MP170 is silent on that matter, simply calling for one coat w/o further clarification. Two coats certainly will do no harm and if you are applying on the thin side to begin with, it's probably advisable.

Rod