I would get input from NACE.

 

Lets see if this tag thingy works. @NACE

 

From further research after reading until wee hours of the morning, I think my next course of action is to determine the existing finish. Basically, if it's PVFD, (Kynar, Hylar, etc), I could just prep with a good DTM bonding primer, followed by an acrylic DTM, (although it's always confused me a bit why they recommend primers under a DTM topcoat). If it's anything other than PVFD, I can prime with a rust-inhibitive acrylic primer and topcoat with an elastormeric.

Only problem with the above paragraph is I have absolutely no idea how to identify a 30 year-old factory baked-on finish. None. Right about now is when I'm missing my old paint reps.

 

I did a big roof similar to what you describe on a restaurant a little over 4 years ago in a super dark blue color. It had some rust so I primed with Rusty Metal primer and finished it with SW DTM. One finish coat, applied @6-8 mil.

Given the "electric" blue color, I expected it to fade. It has faded surprisingly little in that time, and has otherwise held up well.

OTOH, I did another one in a dark green, with Pro-Cryl as a primer, and the same finish around the same time. It has faded noticeably.

I think the difference I see there has to do with the nature of different colorants. Green is going to contain some yellow pigment, which I understand fades faster than other colors. Has something to do with organic vs inorganic pigments I think.

The actual color you paint it will be a factor in how much it fades. I've heard the explanation as to exactly why that is before, but the details elude me right now.


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Btw, I have used Pro-Cryl several times on roofs and always been impressed. It has tenacious adhesion to a variety of substrates and is pretty rust resistant provided no existing rust is present. (Or is removed/converted before priming)


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Thanks for the insights Josh. Are you saying you used Pro-Cryl for the primer, then Sher-Cryl as the top-coat? (since Pro-Cryl is their industrial universal primer). If I end up using SW and the existing coating is Kynar, I'll probably use the Sher-Cryl as the topcoat with their DTM Bonding Primer, which I believe will hold up better than their Pro-Industrial Acrylic DTM. I will give them a lower-tier option of using the Pro-Industrial Acrylic DTM as well, so they've got some options. I think my initial thoughts of using Corothane might've been overkill, but I'm waiting to hear back from the owners regarding my inquiry to find out their expectations.

I've just read countless warnings and horror stories about product incompatibilities, so whatever I use, I'm definitely going to get a rep to sign off on it.

 

I've done and specified hundreds of these. All the systems you listed will work fine. Preparation, budget, and customer expectations in addition to exposure can determine your choices. Kynar requires aggressive prep and high adhesion primer. We have used an epoxy mastic and aliphatic topcoat that his been on a very high profile roof system in Stamford CT since 2000 without any issues or fade. We did a high profile manufacturing and repair facility for 747 engine rebuild in an acrylic DTM that still looks brand new installed in 1998. Coronado/Corotech makes a very high adhesion waterborne etching primer V175 that has tenacious bond. Top coat with anything. Any of the manufactures listed products will work well, but with Kynar I may use an adhesive primer before the topcoat is specified. Call me if you want to further discuss. No Charge!

 

I know you're a busy man, so I appreciate your time & wisdom. Thank you NACE!