High Build urethane primer vs. Polyester primer

What did I write about corrostion protection? Didn't I specify SPI as different. How many ships have you painted?

All I mentioned was UV. I wont argue about below water surfaces where there is no sunlight, but not above. that is why they are referred to bridge lines and you know if they used poly they would have to scuff the entire thing before it broke down not just paint over it again. You must be referring to the dull powdering gray ships that get repainted every 3 years or the yachts that use polyurethane? I know what they paint yachts with, we are required to paint the surveillance equipment with the same Awl Grip coating they use on those.


actually my response wasnt for you. that was for benklesc. sorry

he had asked about corrosion protection which is what i am referring to. not uv durability or chalking. you are right, awlgrip is a great finish for marine but the first step for that is their 545 epoxy primer to provide the adhesion and if on metal the corrosion protection. they dont even have a polyester primer. even their high build surfacing primer is epoxy.
 
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All the poster mentioned was no surface rust on polyester. Epoxy is great, but it is as old school as wash primer and eventually will fade away like leaving it in sunlight.

Automotive refinish epoxy is hardly "old school". Poly and wash primer have been around much longer. Around 1990 is when epoxy started to become mainstream.


They sell polyester primers with zinc chromate in them, that have to be applied to bare metal. They etch into the metal to seal out moisture.
Not true, it does nothing to seal out moisture it is an additive to the poly which is supposed to help it resist corrosion. Poly primer is basically sprayable body filler and it is pourous. Be careful what you read on the internet then repeat. :rolleyes:
I would love for Barry to weigh in on this as he is the Chemist here. He can tell you in no uncertain terms why epoxy is superior. Adhesion it is no contest, epoxy wins hands down. Chemical resistance, epoxy is far superior to poly and wash primer isn't even worthy of mention. Corrosion resistance it is superior as well. It provides a true and complete blocking layer between the atmosphere and metal. If it wasn't the absolute best choice all OEM's would not recommend that it be used under any refinish/repair work.
We've had an Evercoat rep at our Shop sing the praises of the hybrid polyester primer. I just nod politely. Adhesion is still the same which means if you don't use epoxy first the stuff will chip very easily on something that is driven.
Like Crash said why muddy the waters with a secondary discussion about UV resistance? But you must not be talking about SPI Epoxy because it does have UV resistance (thanks Barry) and remember not all epoxy is created equal. PPG DPLF is nothing like SPI Epoxy and nowhere near as good. Axalta doesn't even have a true epoxy, just hybrid stuff.
 
As Chris said, Polyester can't be a quality moisture barrier. It is, after all, basically sprayable body filler. Any one who has done any bodywork at all knows body filler will absorb water like a sponge.

There will be nothing but epoxy on my bare metal!

John
 
actually my response wasnt for you. that was for benklesc. sorry

he had asked about corrosion protection which is what i am referring to. not uv durability or chalking. you are right, awlgrip is a great finish for marine but the first step for that is their 545 epoxy primer to provide the adhesion and if on metal the corrosion protection. they dont even have a polyester primer. even their high build surfacing primer is epoxy.

Yes, I know that since my customer requires me to chromate the part since the insides are all ground surfaces and we had to deviate to mil spec epoxy since it allows to be sprayed over chromate. Their response to me using the system was to chromate the part, mask it, then sandblast the painted surfaces so you can put their epoxy on it since that is what they recommend. Mind you, the majority of their customers are painting 60 foot long masts. And, no, I would not use Mil spec epoxy on a car. All the good stuff that makes it stick is getting removed due to RoHS concerns. Barry has the 80 grit scratch requirement and the problem comes in to what gets between the epoxy and base metal when coatings are used..

I did not see his post as mentioning a long term solution, just a car sitting waiting for work to get done. I know it seems like Epoxy might have really just come into play, but you look at 1990 and that was three decades ago, and I am sure Barry can probably tell you the ingredients that might be getting harder to come by or making it so expensive that they will force companies to give up.

Just knowing there is alot of good stuff out there and me preferring to use a CAT spec paint on frames I cant powdercoat is just one example. There is a place for everything and epoxy's main point is under.
 
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