Final sanding before basecoat

Hey everyone,

I just finished block sanding the 2k high build primer on my truck at 120 grit.
I sanded through to bare metal in a few spots.
It could probably use another round of 2k high build and blocking but I think its satisfactorily straight.

So what I am wondering is what I should do to prepare for basecoat?

Should I spray a coat or two of epoxy and then sand that up to 600 grit (its a metallic paint btw)
Or should I seal the bare metal with epoxy then spray another round of surfacer, sand that to 400 grit, and spray a reduced epoxy as a sealer a few hours before spraying the basecoat?
Or something else entirely?

Thanks in advance!

Several ways you could go, but here is what I would probably do in your situation. Being you sanded with 120 grit you are going to need more material to fill the 120 scratches. Spot in all the bare metal areas with epoxy, next day 2k all over,at least 3 coats, then another round of blocking. Starting with 180- 220 dry then 400 wet. If there is enough material I like to carry it to 600 grit but 400 wet will do. Then seal with epoxy or urethane and you are ready for basecoat.

Thanks for the info Chris.
I think I will follow your advice,
but 3 coats of the high build 2k seems like a lot, if I sprayed that much would I have to worry about leaving too much on if I didn't block it enough?

Guide coat it and block it till you remove all the guide coat. If you blocked with 120 and are down to metal in areas spraying 3 more coats and blocking with 220 then 400 will be fine.

SilentLlama said:

Thanks for the info Chris.
I think I will follow your advice,
but 3 coats of the high build 2k seems like a lot, if I sprayed that much would I have to worry about leaving too much on if I didn't block it enough?

Click to expand...

Spraying any 2K primer over 120 makes me lose sleep at night, I'd go over the 120 with 150 at the very least, then shoot the 3 coats with the HB 2K. YMMV.

Curious to know what the general consensus is about the final grit before 2K.

I've seen guys do it over 80 grit. (they weren't hacks either)I've shot over 120 multiple times no issues. Observe the flash times, give it several days to cure, shrinkage is not an issue.
Years ago I met Hershel "Junior" Conway, who at the time was considered one of the absolute best in the world. This was in 1990, (I was barely 19 ) he was using Sikkens or Glasurit 2k. I don't think he was using epoxy as his base as I don't remember anyone using it then. Think it was an etching primer. He would do his initial blocking with 80 grit, then recoat and sand with 120-150. Re-coat and sand with 220 then 2 wet sands. 3 drys and 2 wets each round of sanding preceded by priming. He told me main thing was to let it flash and give it time to dry/cure. He would let them sit up to a month if he had time. But he said a few days in the sun was good for 99% of the stuff out there.
Here's a Ferrari he recently did (he's in his late 70's now)


He was so well known for the quality of his work, back then (late eighties early 90's) guys were bringing him brand new Ferraris and having him repaint them. There were 2 of them in his shop when I visited him. He would strip them down like any other car and start from the metal up.

Chris_Hamilton said:

I've seen guys do it over 80 grit. (they weren't hacks either)I've shot over 120 multiple times no issues. Observe the flash times, give it several days to cure, shrinkage is not an issue.
Years ago I met Hershel "Junior" Conway, who at the time was considered one of the absolute best in the world. This was in 1990, (I was barely 19 ) he was using Sikkens or Glasurit 2k. I don't think he was using epoxy as his base as I don't remember anyone using it then. Think it was an etching primer. He would do his initial blocking with 80 grit, then recoat and sand with 120-150. Re-coat and sand with 220 then 2 wet sands. 3 drys and 2 wets each round of sanding preceded by priming. He told me main thing was to let it flash and give it time to dry/cure. He would let them sit up to a month if he had time. But he said a few days in the sun was good for 99% of the stuff out there.

Click to expand...

Good to know that is doable, most of the shops I've used the 2K or the shops I sell SPI to are collision shops that prep and paint the same day or the next, the primer never sits on for days so I always recommend 150.

The epoxy I have done 120 without any issues down the road.

Keep in mind this would be for custom/resto type work. Insurance type work would be a different story. Insurance/Collision repair I finish everything with 180

I use a slow reducer in my Turbo 2K Primer as not to bridge the 180 scratch, now this is for higher end collision and resto work.

Great info, thanks for the help.

What is the potential concern with spraying the 2k over lower grit scratches?
Is it that it can bridge the scratch like El Toro mentioned?

Also the tech sheet says that you can sand the 2K 30-60 minutes after spraying but I gather that would be a mistake?

In Perfect world body filler should be finished in 220 grit and 2K sprayed nice and wet with 30 to45 mins flash time between coats and let sit 30 days in sun and finished in 800 before base coat,but we all know in the collision shop will never happen. And concern with spraying over lower scratches with to dry and fast reducer the 2k will not flow in the the scratch but will just bridge over and will show up later. I love to let my 2k sit over night and longer if possible.