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Hi, I pretty much agree with CNKS and will add a couple of thoughts. By "retarder" I assume you are referring to reducer. OMNI does have a real "retarder" (MR189) but that should NOT be what you want. I personally would never use the slow (MR187) reducer in the 60's - I don't care what your dealer says. I like to apply fairly heavy coats and using a slow reducer in temps that low would be run-city for me. Here's my own interpretation of the temp ranges for the OMNI reducers and hardeners used with OMNI MTK acrylic urethane topcoat: MR185 - fast reducer - 60-70F
MR186 - medium reducer - 70-80F
MR187 - slow reducer - 80-90F
MR188 - very slow reducer - 90'sF MH167 - fast hardener - 60-75F
MH168 - slow hardener - 70-85F
MH169 - very slow hardener - 80-95F These ranges seem to work best for me. Sometimes I will tend to go to the next slower than indicated above if I am at the high end of a range. For example, if I was at 78F, I might choose the MR187. But that's just me. Others can push it farther above or below. There is really no hard and fast rule. It depends on your own technique to a large extent. The slower products will tend to produce more runs and the faster products will tend to produce more orange peel if you get too far outside the "normal" ranges. I recommend some practice painting on something you don't care about if you haven't used these products before. I'd not pay any attention to the AU label on the epoxy. I don't know why PPG puts that label on there except to signify that their epoxy is a "urethane class product". It's certainly not a urethane in the sense that the MTK topcoat or the MR182 surfacer are urethanes. What you "need" for your own respiratory protection when using urethane products can only be decided by you. I'll tell you this - your dealer doesn't know, probably doesn't care and is not the best one to advise you. I'll also tell you this - 3M doesn't make a chemical cartridge that they recommend for use with isocyanates when the actual exposure level is unknown, which is always the case for DIY environments. For such situations they recommend supplied air - period. It's always easy to play fast and loose with someone else's health. Different people have different tolerance levels for exposure to isocyanates and I always recommend supplied air when dealing with isos. That's what I do myself. I learned it the hard way years ago. If I won't do it myself, I simply won't recommend it to others. Regulator at gun? You really don't need that. Just use a pressure gage at the gun and adjust your upstream Sharpe regulator to give the 21 psi at the gun with the trigger pulled. Rod
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