Sorry- this is a bit long,
I'm sure this has been covered- but didn’t find any info on it. I'm doing a full -down to the frame- restore to an 87' BMW 325. I’ve spent 3 years and about $23k (for personal reasons) getting to this point and am now ready to start putting it back together. Over the next 2 weeks I need to prime the body/frame, weld in the new quarter panels, and finish painting the car. I know that doing the "paint/prep" right is the first step to doing a wonderful restore, but wonder sometimes if I'm being to "anal". I'm spent too much time and money on this project to screw it up now.

So.... I’ve sandblasted the body down to the steel (more then once-flash rust) and having a real problem with flash-rust. I live in Seattle and was hoping to be painting during the summer- but now it's fall (fall/cool/RH going up/flash rust with in a week).

1st question:
After sandblasting can I 2-part/epoxie primer directly over the sandblasted surface or do I need to sand down the SB surface b-4 primer? Seems like I read somewhere that you need to sand down a SB surface b-4 primer. I’m using the full line of “House of Color” paint products, 2-part Poly, CB/CC.

I spent the summer stripping (sand blasting) every inch of paint off the body and another month hand sanding the body down with 120 grit. By the time I got to this point- a week later- I start to get a light haze of flash rust. So the last two days I "spot sandblasted" and now I'm back to a mostly sandblasted surface. I have a bottle of SEM 39308 ($$) Rust-Seal and was wondering if I should spray a coat of this until I’m ready to prime (a week or two later), but the directions say not to use over a sandblasted surface. Or maybe I shouldn’t us this product at all? I told the guy at the paint store about my flash-rust problem and this is what he sold me at about $30 bucks a pint. I do plug in a dehumidifier at night in the shop to hold down the humidity. We haven’t started to hit our (Seattle) rainy season yet, but are only days away before it starts raining every day for the next six months.

So my questions are:
Do I need to hand-sand the SB surface before primer, or can I prime over a sand blasted surface for the best result- I want to do it right but time and humidity is working aginst me (I’m working as fast as I can)?

Should I use the Rust-Seal for my flash rust problem, or am I asking for problems in the over all quality of my paint job by using this product…

For best results you should sand it with 220 but you can for now just put a etching primer or vinyl wash right on it withought sanding and just wipe it off with any thinner when you are ready to sand it down properly

You actually sandblasted the entire body, more than once???????? There isn't going to be a straight panel on the vehicle...

I have to deal with the same problems with flash rust. Acid rain all year with sea water spray, oh boy.
The only way to properly do it is to sand in sections and epoxy the same day. On my project I sanded the whole passenger side with 80 grit on a DA, wiped with W&G remover then primed.

Don't expose more metal than you can cover by the end of the day.

Yeah man we use the self etching primer in the can ASAP when we have stuff sand blasted down to bare metal. The dupont stuff works great and is way easy to spray!!!

ZRX61 wrote:You actually sandblasted the entire body, more than once???????? There isn't going to be a straight panel on the vehicle...

I stripped this car down to the frame...every last nut, bolt and washer has been removed. I chemically stripped the panels and roof by hand. I only sandblasted the main frame. BMW goes to great lengths to rustproof their frames (dipped), so I went with sandblasting (myself) instead of a chemical dip. I'm the original owner of this car and know that the internal rustproofing was still intact and healthy.

I lost a quarter panel in an accident (Black Ice) a few years after buying the car new in 1987. The shop that did the work (a shop recommended by the BMW dealership) did a poor job sealing the weld joints (and a few years later the paint failed as well) and I started to get extensive rust in the quarter and tail panel joints, so I decided to replace both Q panels and the tail panel with OEM replacements. I’m $23,000 into this restore (what I paid for the car new in 1987) and it’s still on a frame dolly. But I’ve got cases of brand new parts ready to go on the car at some point. I’m taking my time and it might take a few more years to finish this rebuild to factory specs or higher. I’m guessing I have thousands of hours into this rebuild… but I’m learning as I go… one day at a time.

As far as the Sandblasting goes- I chem. stripped 95% of the frame/shell and only Sandblasted the hard to reach places. When I needed to re-blast any of the flash-rust, I used sand that has been recycled many times over, so it’s more like sand-dust (almost looks like powdered sugar) then raw course sand. So heat and warpage is not an issue.

vwbobby wrote:I have to deal with the same problems with flash rust. Acid rain all year with sea water spray, oh boy.
The only way to properly do it is to sand in sections and epoxy the same day. On my project I sanded the whole passenger side with 80 grit on a DA, wiped with W&G remover then primed.

Don't expose more metal than you can cover by the end of the day.

Thanks for the input guys: Sea water and Acid rain... thought I had it bad...lol

What I'm trying to do here is prep everything that’s going to get sprayed- so when its time to shoot- ALL layers i.e.; primer, sealer, base, clear, flo-clear- is all applied as one unit (all within 48-50 hours) so that each "layer" is still "soft" so all the layers will bond well to each other per the manufactures recommendations, but also making sure every coat is flashed per manufactures instructions - Something like this:

Pre-Paint-
All sanding and body work has already been finished. Any “bodywork” has all ready had 2 coats of primer, block sanded- ready for 1st full coat of primer.

-Quarter panels (undersides) has already been primed and painted.
-All quarter panels and tail panel have been Mig-Welded into place. All welding finished.

Day One-
First 48 hours:
-All “body-joints” have been primed/dried/ and all Seam-Seal has been applied as needed.
-All “blind” panels/rails have been primed/seam-sealed/water proofed.
-All Rubber Coating and Seam Seals has been applied to undercarriage as needed
-Undercarriage has been primed as needed (exposed steel) and full undercarriage has been shot with 2 coats semi-gloss black, dried 24 hours and masked off.

-Body has quick light sanding/dry with 120 grit,
-Body and booth is cleaned of all dust
-Water traps emptied on compressor, Deselent filters activated.
-Paint products and supplies are laid out and organized, spray gun is assembled.
-Clean booth air filters are installed.
-Body is solvent washed and tacked.

Day Two-
1) 9am: 1st coat Primer/dry time 6 hrs (1 coat body, Body work 2 coats).
2) 3pm: Guide coat, Block sanded.
3) 5pm: 2nd coat Primer/2 coats/flash time 2 hours
4) 8pm: Wet sand
5) 10pm: Metallic Silver Primer Sealer/ 2 coats/flash 2 hours
6) 1am: Scuff/wet sand if needed
7) 2am: Midnight Black base/3 coats

Day Three-
8) 7am: Scuff/wet sand if needed
9) 9 am: Midnight Blue Metallic base/3-4 light coats/flash
10) 1 pm: Tack/ 3 coats Clear/ dry time 12 hours min.
11) 10pm: Wet sand
12) 8am: Flow-clear/2-3 coats/dry 24 hours

Day Four-
13) 8am: Polish as/if needed

In a perfect world, everything would go according to plan. You will run into things like:

1) That little patch of sand that flipped up from a random crevice and speckle your fresh primer/paint...Making you have to sand it out and re-prime.

2) The fly that decided to land and swim in your primer/paint/clear, making you start over.

3) the patch of bondo that wasn't properly sanded leaving a large 'holiday' in plain site under your primer.

What I'm saying is, you won't be able to get everything done in the time allotted unless you are lucky or work a long time. The longer you work, the more mistakes you make (at least I do).

Here's how I would do it....
-Prep one panel at a time with 80 grit on a DA, clean, and prime with epoxy primer.
-After primer has been applied to all panels. Shoot entire vehicle with 2nd coat of epoxy. Let stand AT LEAST 24 hours
-Do final filler work, sanding dirt/mistakes out of your primer. There will be a lot more than you expect!!
-Spray 3 coats of filler primer on.
-Block sand like a monkey till your arms fall off
-Fix mistakes, spray more primer, repeat.
About 1 month later, you are ready for paint. Maybe I'm anal, but thats just the timeline I usually get stuff done in..

First off, You said that you sandblasted the body. I hope you didn't warp the panels, as it can be done fairly easilly.

The sandblasted surface is an ideal texture for epoxy primer, if it has not rusted. Slight flash rust is not a real problem, is you are spraying epoxy over it. I would scuff it with scotchbrite, wipe it with wax and grease remover, and shoot. If it is heavier than "Slight flash rust", then lightly sand the panels, with whatever grit to remove the rust. If it is heavy, then 80 grit on a DA would get it clean and ready for epoxy.

Get epoxy primer on everything that is bare metal, then work from there on doing repairs. Any filler needed goes right over the epoxy, and continue on.

Aaron