[wyomingclimber]

I've just finished my filler work and have a car pretty much covered in 80 grit sanding scratches.

I assumed that my high build primer coats would cover these, but in reading the tech sheet, I find that it suggests going to 320 before shooting the primer.

I don't want to do more sanding because I'm already through to bare metal in places. What would you suggest? Skimming the entire car and sanding with 320 before high build? Shooting something like SlickSand?

Next time, I'll read the tech sheet first...

Thanks

 

[sunsetdart]

You do want to sand with at least 320, if not 400 before you apply a filler/primer. I had a filler primer that said it would fill 80 grit sand scratches ....guess what....it didn't.

 

[302 Z28]

Primer shrinks, the smaller the sanding scratch the less it will show when the primer shrinks. Play it safe sand with 320 or 400 then prime.

Vince

 

[markha]

Agreed, but his problem is that he is already down to bare metal in spots. Other than the scratches, is it straight, did you use a guide coat?

 

[alexflacco]

A Poly primer (slicksand, feather fill, etc) will fill 80 grit scratches and will not shrink back. A car covered in 80 grit scratches is the perfect candidate for Poly primer, its more or less glazing putty that you can spray.

 

[wyomingclimber]

Well, it's as straight as it's gonna get

I've got a quart of SlickSand lying around, maybe I'll try shooting that, then sanding w/320 before my high build...

 

[jcclark]

You can sand it finer even with the bare spots showing.
Remember, the finer grits don't level, they smooth.
The primer should take care of the bare spots and paint transitions.
Guide coat it and block and see, you can alwys add more primer (LOL) imp:

 

[cboy]

I've got a quart of SlickSand lying around, maybe I'll try shooting that, then sanding w/320 before my high build...

Unless you have a very small car, I think you'll need more like a gallon of Slick Sand. I shot my sedan delivery project with Slick Sand (pictures below to give an idea of the size) and it required almost a full gallon to get one good coat on it. Granted, there are a lot of parts and pieces and they are all dismantled so I shot them on all sides, but I think a quart of material might be stretching things.

Also, you'll need a pretty big gun tip to shoot Slick Sand or any of the polyester high fill primers. I used a 2.2 mm tip and I believe 1.8 is the absolute smallest that is recommended.

Also, if you are a novice painter like me, be prepared for quite a lot of orange peel with the Slick Sand. It is thick stuff. Best to have some test panels available so you can fiddle with your gun adjustments a LOT. I'm sure the experienced painters on here like JC and Vince can get this stuff to lay down really smooth, but I had to sand out a lot of peel. Purely a case of "good product" in "bad hands" in my case, but just be aware of the challenges associated with the liquid fillers like Slick Sand.

 

[wyomingclimber]

Jclark:
I see what you're saying--the sand throughs are in the troughs of the scratches. Makes sense.

You may have answered a question I've never been able to get an authoritative answer to: Do you go back and epoxy the places you sanded through to metal or do you just shoot the 2k high build over it?

Cboy:

Cool project!

The quart is what I have left--I shot the rest of it on my fiberglass fenders. I found that I had to use incredibly high pressure--something like 40psi at the gun w/a 1.8. Not exactly recommended by the gun manufacturer, but it kept the peel to a minimum...

 

[jcclark]

The best way is to spray epoxy over any/all bare steel.
Most 2K primers are not for diresct to metal but even those say
it's ok for small spots like silver dollar size exposures.
For my collision repairs I just cover them with 2k,
it's never been a problem. Most body shops do the same thing.
If you are concerned about that, some will spray a little
etch primer on the bare metal first, even from a spray can.
I don't think it'll ever make a difference in the long run.
Back before I knew better I painted an entire car, stripped
to the bare metal, with only 2k primer.
My son drove it for years, never a problem. imp:

 

[daves66valiant]

I'm a total newb as well and have run into this before on my first project. I did all my body filler work over epoxy. Filler was finished with 80 grit. I ended up sealing my filler work and bare metal spots again with black epoxy and then shot 2 coats of gray Featherfill (1.8 tip worked great my gun pressures were increased per instructions no OP). You can reduce the featherfill too. I blocked almost all the featherfill off the car. With the gray on black it acts as an extra guide coat besides the 3M drycoat I used. You could actually see the filled 80 sanding scratches. Then I used my 2k primer for final blocking to 600 wet. Then a sealer coat of reduced epoxy before basecoat.

This is probably over kill but this is a full restoration and I want it to last a very long time.

 

[acer2162]

Change grit in 100 grit intervals self etching primer over bare metal dry to recoat time of product spra th e 2k primer

 

[acer2162]

Bondo work to 180-220 grit featheredge with 320 grit to the wnd of your primer area then scuff with red scotchbrite works for me from airplanes to cars 12 to 15 a week

 

[Underground]

I'm a total newb as well and have run into this before on my first project. I did all my body filler work over epoxy. Filler was finished with 80 grit. I ended up sealing my filler work and bare metal spots again with black epoxy and then shot 2 coats of gray Featherfill (1.8 tip worked great my gun pressures were increased per instructions no OP). You can reduce the featherfill too. I blocked almost all the featherfill off the car. With the gray on black it acts as an extra guide coat besides the 3M drycoat I used. You could actually see the filled 80 sanding scratches. Then I used my 2k primer for final blocking to 600 wet. Then a sealer coat of reduced epoxy before basecoat.

This is probably over kill but this is a full restoration and I want it to last a very long time.

If you blocked that much and STILL had to spray high build over the featherfill, you 1) didnt put on enough primer or 2) didn't get the bodywork straight enough in the first place. FeatherFill will fill smaller hail damage. It will fill 36 grit grinder marks. BUT it DOES NOT replace repairing the areas properly. Reduce it with acetone and it sprays smoother. If you put 3 coats on and block and it still isnt straight, you were NO WHERE NEAR ready to prime.

 

[jeremyb]

It doesn't matter how laser straight you get your panel(s) in filler, as soon as you put poly or high build urethane on it and go to blocking, you'll think you didn't even block your filler in the first place. That's why you prime block primer block and repeat as necessary. The object with poly is to block off as much as you can without going too far. It needs to be just like a skim coat of glaze when you are done.

 

[shine]

i start priming at 80 grit. then 100 for blocking primer. last coat of primer will be 320. shoot your primer wet. if not you will bridge the scratches then it will dry into them. any primer that requires 320 to 400 is not worth using in the first place. what good is it ?