Finishing grit for poly primer before urethane high build

[DCx]

What is a good grit to finish my poly primer to before I move on to urethane high build? I am using Eastwood Contour Poly and its FRIGGIN AMAZING! spraying it on with a cheap ebay 2.5 tip gun at 37psi with 4% reduction (twice activator volume) acetone and it lays down pretty smooth. Still a slight orange peel but I spray a heavy guide coat and hit it with 80 grit and its easily reduced to a fine powder that doesn't load up my sand paper.

Here was my plan:


spray 3 wet coats of poly
guide coat
block with 80
guide coat
block with 180...
???????


that's were I stopped. I scuffed up a small section of 180 with some 240 and man is it smooth! still have material to sand.

do I stop at 180? go to 240, then 320, then urethane, 320, 400 wet.

OR

do I stop at 180, red scotch brite it then move to urethane, 320, 400 wet.

https://static1.pt-content.com/images/pt/2021/05/S5WB4qm-1.jpg
Fresh Poly

https://static1.pt-content.com/images/pt/2021/05/5hMQZSe-1.jpg
Blocking with 80

https://static1.pt-content.com/images/pt/2021/05/3oHeyoz-1.jpg
blocking out 80 scratches with 180 and lightly sanding with 240 by hand with an interface pad

https://static1.pt-content.com/images/pt/2021/05/E0nfvI5-1.jpg
Fresh poly on the body of my dads 67 Fastback

[dhutton]

Any quality 2k urethane should fill 180 scratches. I use SPI Turbo primer. Not sure I would trust the job to Eastwood/Kirker 2k.

Also would not apply that poly on bare metal. Quality epoxy only on bare metal.

Don

[Tsaints1115]

I'm sure the material spec sheets would have exactly what the manufacturer recommends for proper adhesion. Paint's a big dollar investment. I wouldn't guess on it.

[dhutton]

I'm sure the material spec sheets would have exactly what the manufacturer recommends for proper adhesion. Paint's a big dollar investment. I wouldn't guess on it.
Keep in mind tech sheets are directed toward collision repair, not restoration work. Huge difference in goals etc….

Don

[Tsaints1115]

Keep in mind tech sheets are directed toward collision repair, not restoration work. Huge difference in goals etc….

Don

Proper paint adhesion is proper paint adhesion. And collision repair is a huge chunk of the market compared to anything else so the last thing they'd want is warranty claims on any paintwork.

[dhutton]

Proper paint adhesion is proper paint adhesion. And collision repair is a huge chunk of the market compared to anything else so the last thing they'd want is warranty claims on any paintwork.
Yessir! Sounds like you’ve painted a lot of cars and you know your stuff….:hail:

[Tsaints1115]

A baker's dozen or so.

[DCx]

Any quality 2k urethane should fill 180 scratches. I use SPI Turbo primer. Not sure I would trust the job to Eastwood/Kirker 2k.

Also would not apply that poly on bare metal. Quality epoxy only on bare metal.

Don


I unfortunately live in California and about the only SPI products I can get my hands on are Epoxy and waterborne wax and grease remover. I have SPI epoxy on hand. I didn't strip the car to bare metal because of how pristine the existing old paint was. I just hit the car up with some 80 grit and shot the poly over it. The trunk deck had one tiny ding in it I used some glaze on.

The 2k urethane high build I have on hand is Upol system 20. its 4:1 and was recommended to me by my local auto body supply.

so the task at hand... do I stop at 180 and shoot the 2k high build or sand the poly as far as I can go?

[dhutton]

It’s not in the tech sheet but it should easily fill 180 scratches imho. Hopefully the paint god will approve….

https://www.u-pol.com/files/31617/up2253v-TDS-EN

Don

[Tsaints1115]

It’s not in the tech sheet but it should easily fill 180 scratches imho. Hopefully the paint god will approve….

https://www.u-pol.com/files/31617/up2253v-TDS-EN

Don


188801

[dhutton]

The last Paint God on here went to prison…. :razz:

Don

[Tsaints1115]

Nothing wrong with consulting directly with the manufacturer. Even a rattle can of Rustoleum has the prep, spray, recoat, and drying specs on it.

[DCx]

I ended up taking the entire thing to 320. I was pretty amazed how easy it was to remove 180 scratches with 320. Only gripe is my spray on guide coat clogged the 320 pretty bad. All in all I am happy with it, feels glass smooth. Poly is pretty much transparent, I have a few metal spots showing but its getting coated in 2k urethane primer tomorrow. I will try to wet sand it with 400 some time in the future. I am still working on the rest of the car.

should I use rattle can etch on the metal? my Upol primer states its DTM.

https://static1.pt-content.com/images/pt/2021/05/nyoPIdv-1.jpg