What would you do with 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

[TooMany2cvs]

I think I'd be tempted to put some high-build primer/filler on, then a guide coat, and see what I've actually got.

I wonder if a 2002 would look silly with a vinyl roof? Or there's always the Webasto option...

[philh]

I use dinitrol rust converter on surface rust to kill it, just paint on and leave. Then id etch prime it, not sure if filler primer will be thick enough, you may need to put a thin skim of filler across the roof,flat then use filler primer.

[austin]

Submerge it in water and connect it to a battery charger.

It may sound odd but it works.

http://www.instructables.com/id/Electrolytic-Rust-...

Might struggle finding a bucket big enough for a whole shell though...

[droopsnoot]

I've done various forms of rust removal with my current project, and had similar (but not quite as bad) pitting in the roof. Electrolytic removal is very effective, I've heard of people using stuff like a sponge or a blanket as the electrode for parts that cannot be immersed but I've never tried it myself.

I ended up using some sulphuric acid (in the form of phDown, a hydroponics acidity modifier widely available) to clean as much out as I could, and I also used my cheapo Aldi spot-blaster (but with some other media, not the stuff that comes with it) to try to clean out some of the pits that didn't look as clean as I'd like. Once that was done, I covered the roof in epoxy primer, then I've covered the pits either in standard body filler, or stopper where they're much smaller. Next plan is some high build primer, then top coat.

I am hoping I've done enough, and really don't want a vinyl roof on the car. I did consider a Webasto as I have a spare one and I do really like the extra light when it's open, but I don't much like the extra flex that I might have (it might just be the way the car is, even if it had a solid roof) and the section of the roof I'd have to cut out was pretty much the best part of it.

[DeanR32]

Cheers for the replies lads

The roof will need flipping (i think that's what it's called), and a skim of filler. It's far from perfect. I've got some Bilt Hamber hydrate 80, which I understand is the same as all the other rust coatings (grey fluid which turns black once it's done it's business), but I'm worried it can't be filled over the top of it.

Phil, does your method get good results (as far as you can tell so far)?

Cheers again

Edit. I must have been writing my reply as you posted yours Droopsnoot.

I like the sound of the spotblaster. I might grab one and give it a go. Out of curiosity, are you spraying or brushing the epoxy on?

Edited by DeanR32 on Tuesday 22 September 12:23

[philh]

Yes used this on a B and a mate did the same on a herald that had been left like yours and no problems

[droopsnoot]

DeanR32 said:

I like the sound of the spotblaster. I might grab one and give it a go. Out of curiosity, are you spraying or brushing the epoxy on?

Spraying. I tried brushing it and got terrible brush marks. I might have got away with thinning it out further, but I gave up and sprayed it instead. Way better finish, even with my lack of spraying experience.

[DeanR32]

Ok mate, cheers

I suppose I could look into spraying it. I'm in a lock up with all the gear, so could try it out. Whatever coating I use will need to be able to take filler on top of it.

[tapkaJohnD]

A "strong" acid, such as sulphuric will act on the native metal as much as the rust.
Better, a "weak" acid, an organic. THat will attack the rust, but not the clean metal. Vinegar, acetic acid, will do the job, but phosphoric acid has the property of forming iron phosphate which is insoluble. This is deposited on the work and when dried forms a hard, black coating that is a good foundation for primer. Phosphoric is, of course, the basis for the proprietory 'rust eaters', but can be bought by the gallon as "Milkstone Remover" for about £12 - and you will need a gallon, or two, for that roof!

Vigorous cleaning of thick rust, and oil/grease, of course, then brush on and leave soaked paper kitchen/garage towel on the surface overnight.

John

[DeanR32]

Cheers for the input Tapkajohn

I've got some phosphoric acid gel (not sure on the acid content, but you can surely smell it!) which I coat on and leave for half hour, but it tends to dry and get a bit tacky. I like the milkstone remover idea. I'll grab some of that.

If there's any other products you lot can vouch for, I'd be very grateful to hear of them. I need to get this car done by June for Le Mans!

[droopsnoot]

And to update, phDown is actually phosphoric acid, not sulphuric as I wrote above. I've been using Milkstone remover to soak smaller stuff in, diluted 50/50 with water, and it's reasonably effective. I've heard tell of mixing with wallpaper paste to make it form into a gel for stuff you can't soak, but never tried it myself.

I chose epoxy primer because it's not supposed to sink once it's gone off, so adding filler over the top shouldn't cause trouble. Of course, I won't know for sure until I've done all the top coat and put the car back together.

[DeanR32]

Cheers for the input Droopsnoot

Epoxy seems the way to go on any forum I've looked on. I'm just worried about the application of it. It seems it's best sprayed on. I may have to thin it down enough to brush/roll it on the roof and other areas, and use etching primers on the bodywork that needs a good finish for paint etc

I could do with giving the painter a good head start to keep cost to a minimum.

[v8250]

OP, you may like to treat the roof surface with Built Hamber's 'electrox' first. Then use their high build primer to cover any/all imperfections. I've used these products and they work very well. Only use the high build once you're ready for respraying the car/roof. The big advantage with high build is that it can be flattened with a good surform sanding kit giving excellent results, see here for more info'...

http://www.bilthamber.com/paints-and-coatings/elec...

http://www.bilthamber.com/paints-and-coatings/high...

http://www.amazon.co.uk/Sanding-Blocks-Hand-Kit-pi...

[DeanR32]

Cheers for the reply v8250

I should give Bilt Hamber a call and find out if the electrox can be filled over, as it'll certainly need a skim over. I'm just st scared of not doing enough prep before painting.

Maybe I need to crack on with it and see how it holds up

Cheers again for the replies

[DeanR32]

Does anyone know where the hell I can buy Milkstone remover or ph down from? Would B&Q or such do anything like it?

[Hamish Finn]

Agricultural merchant.

[The Surveyor]

OP, have you considered getting the roof soda-blasted. The dust will get everywhere but it would ensure that all remains of the rust will be removed without any risk of buckling the metal?

Once the rust has 100% gone, etch prime then either a hi-build primer or light skim of filler to smooth it out.

[droopsnoot]

DeanR32 said:

Does anyone know where the hell I can buy Milkstone remover or ph down from? Would B&Q or such do anything like it?

My phDown came off eBay, it's a hydroponics product so if you've got any kind of place locally you might be able to save on postage. Milkstone remover usually comes from farm suppliers as that's the main use for it - we had a Countrywide store fairly locally that I got mine from.

Many of these things are basically the same chemicals packaged differently. I am convinced that Deox-C is actually a packaged version of citric acid - it looks the same before you mix the powder with water, and it acts the same. Citric acid is relatively cheap though.

[Astacus]

What you need, and I speak from painful experience, is bilt hamber detox C gel. It is a paint on acidic gel that will clear off that rust quite easily. You will need to do it several times, leave it over night each time, then wash off and scrub with wire wool and repeat. I can't praise it highly enough for stuff that can't be dunked. Anything that can be dunked, dunk it in a bucket of Deox C powder made up in warm water over night, scrub and repeat till its clean grey metal. I've also used the gel on stuff that had been badly sandblasted to get the last remnants of rust out the pits. Nothing is going to give you back the oxidised metal, so you will always have the pits.

After I would use an etch primer then spray and rub back high build until stisfied with the finish