body and interior How to tackle this roof

[DeanR32]

This is the roof on one of my BMW 2002's. The previous owner has stripped it to bare metal and then left it in the elements. As you can see, it's pitted in most places, and I'm worried about leaving any rust in the pits.

I've got a phosphoric based rust remover/neutraliser which is seems to turn the rusty areas black.

My process is:

Knotted wire wheel to take the top stuff off

Brush in acid based gel and leave to work.

Agitate with wire brush

Wipe off acid gel

Wire wheel the area

Repeat a couple more times.

After all this, it leaves me with the above result. Do you think I've done enough and should put a precautionary coat of rust cure stuff and be done with it? Or haven't I done enough? Shiny metal would be lovely, but I reckon if I remove the pits, I'll be taking too much metal off. The roof isn't the strongest one I've felt already!

Any comments/suggestions welcome

Cheers

[Simeon]

Ideally you should get that media blasted.

 

If you can't do that for any reason then what you are doing sounds OK. Just be sure you neutralize all of the rust converter. I would wipe off with a water soaked cloth and then follow up immediately with wax & grease remover which will displace the water and then flash off dry. You don't want any rust killer chemicals left under your paint. Go over it with #80 discs on a DA sander until everything but the pits shines before high build epoxy primer.

[TobyB]

Agreed.  

 

t

[Beemeup]

I'd get rid of all of the rust with the ospho, then prime it with an epoxy primer.

Edited September 23, 2015 by Beemeup

[DeanR32]

Thanks for the replies guys

If I follow your steps and go with the epoxy primer, can that take a filler over the top (bondo to you guys)? As it will certainly need one!

[ar_kid]

Go easy with the wire wheel and what looks to be a polycarbide wheel in the background as they can generate a lot of heat, an MBX blaster would be the ideal tool for that.

Rgrds

[Simeon]

Big debate about filler over primer vs primer over filler. My personal preference is filler over primer (and then more primer to seal it in). You have to ensure that the primer is keyed with #80 before application. Consult the tech sheets for your products as they take precedence over everything (including internet dudes).

Edited September 23, 2015 by Simeon

[Beemeup]

Thanks for the replies guys

If I follow your steps and go with the epoxy primer, can that take a filler over the top (bondo to you guys)? As it will certainly need one!

Yes, absolutely. I've done it many times, no issues at all.

[JohnH]

I'de be very concerned about using a non stainless steel brush. Little bits break off, embedding themselves into the surface, seeding further rust. 

[esty]

clean it

 

sand it with 80 grit,

 

prime it with epoxy

 

do any necessary body work

 

final sand with 320 grit

 

hi build urethane primer

 

sand with 600 grit

 

paint

[DeanR32]

Thanks for the replies lads

I've been thinking about the epoxy primer, and what one to use, as ideally I'd want to brush/roll it on. I know spraying would get better results, but I want to use this on the roof mainly. Etching primers may have to do for the rest of the exterior.

If you guys have any other tips, I'm all ears, seeing as I've never undertaken this sort of project before.

Cheers

[Simeon]

Think about what you want out of this paint job. Rollers can of course be used but it is never going to look stunning. The cost of materials are the same (expensive). Do you really want to spend all that money and have it look like it was painted with a roller?

 

Have a look in Exchange & Mart (or whatever is the UK free ad paper / website now) and look for someone to do you a cheap spray job if you do the preparation. It shouldn't cost a lot, might not be perfect but better than what you can realistically achieve with a roller.

[Beemeup]

Unless you plan to cover the roof with a vinyl top, I recommend against rolling. It will go on much too thick and will look terrible. Get yourself a spray outfit and do it right. Even a cheap rig from HF works good enough. Heck I've been using their low-buck spray guns for decades. They work great as long as you keep them clean and in tune.......like any other! I'd use the epoxy for the entire car. I don't see the benefit of an etching primer. Also, make sure to use a primer that is compatible with whatever finish paint you want to use. I've been using Summit Racing's line of primers and paints. I think it's made by Sikkens for them. Great solids content, so it flows and covers well, excellent results so far, and quite affordable. Unless you're going after a concourse quality restoration, I highly recommend this brand.

Edited September 24, 2015 by Beemeup

[Redtail]

I'de be very concerned about using a non stainless steel brush. Little bits break off, embedding themselves into the surface, seeding further rust.

How could adding microscopic bits of mild steel to a panel that is mild steel seed more rust?

I'venever used a stainless wire wheel and been fine.

[TobyB]

Personally, I'd use the 3M strippy pads, as they seem to get almost to the bottom of the rust pits, if you're diligent and careful, and don't heat AS MUCH.... but still some.

 

As to wire wheel, mild steel will be fine as the etch treatment can get at it.  Stainless is a bigger deal on aluminum, for example, if you're going to try to weld it or surface prep it.

And a good clean and quick sand over bare metal before you apply the first product layer is always good insurance for many things... dents, not the least!

 

Don't roll the primer.  The stuff is really tough, and while you could probably sand high- build primer straight, the epoxy will resist sanding enough that you'll never get a perfectly

straight roof.  Spray it.  It'll penetrate better.  And I have used a very light coat of etch prime under the epoxy, for surfaces much like yours, then sanded, filled, sanded, filled,

re- epoxied, high- build primered, sanded re- epoxied and painted in lots of different iterations.  It's all worked.  The only failure I had was that I once failed to get all the aircraft

stripper off a hood...

 

hth

 

And yes, believe the sheets that come with the material over ANYTHING we- all say!

 

t