Rust treatment

I have some steel car bodywork that's rusty and wants treatment - mostly exterior edges of wheel arches. I think the metal is good underneath, so it's just surface rust.

On another car I treated this sort of thing by scraping off the surface rust, treating with Jenolite, then two coats of Hammerite, then spray colour. But the rust continued to spread. In that case I can't be sure the rust wasn't just coming through from the other side, so nothing would stop it.

I've been sanding off the rust with sandpaper and a sanding block, and some good metal is coming up, but it's quite pitted and will take an age to sand off all the good metal to make a flat good surface.

I've been thinking of using a wire brush in a power drill, something like one of these:

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anyone recommend a type? I don't have a lot of space to work in, so something small would be good - I'm assuming I want one with the wire at right angles to the drill shank. How quickly do these get used up (ie do I need to buy ten like I would sheets of sandpaper)?

I obviously need to wear gloves and goggles - is there any other protective equipment I should wear when flailing? Are these wire strands as dangerous as the ones you get from angle grinders?

Once I have bare metal, what's best to prime it? Use the Jenolite to treat the surface? Or straight Hammerite? Or I've heard it suggested using zinc primer (Zinc 182?), or an epoxy-based primer. I already have some Jenolite and black Hammerite. This time I'd like to try using the manufacturer's paint to get a colour match (a few bits are more conspicuous than undersides of wheel arches, where I might just stick with Hammerite).

And for bits that aren't visible (not cavities), I've heard various suggestions of using something like penetrating Waxoyl/Dinitrol, or just engine oil. Anyone any opinions? The underside has already been undersealed but the underseal is broken in places. I know this is completely the wrong time of year to do this, but not a lot I can do about that except copious application of the hairdryer... (or is it better to leave untreated until summer rather than seal in moisture)?

Thanks Theo

Reply to
Theo Markettos
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> Can anyone recommend a type? I don't have a lot of space to work in, so

It's a long time since I did that kind of thing but you would really be better off with an angle grinder with flexible disc which would do the initial preparation in minutes. AIUI the best material for reinforcing and building up the surface for a long term repair is lead rather than body filler, and the following link may be useful if you decide to go down that route:

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Reply to
Djornsk

Interesting... I hadn't thought of that approach. Is 'tinning' the surface the final treatment, or does it need further painting? I have one small dent that needed filling and I've filled it with 'Isopon' epoxy filler - but that was easily sandable down to bare metal as it only had light rust.

This surface is upside down, so anything that requires gravity to attach isn't going to work - solder paste might stay on by surface tension, but significant blobs of molten solder wouldn't.

Do you need a serious hot air source? I just bought a cheap hairdryer as I couldn't see the difference between that and a cheapo hot air gun - but I doubt either would be hot enough to metal solder. Gas torch?

Theo

Reply to
Theo Markettos

Scraping rust off isnt thorough, to get it off you want a wire brush in an angle grinder. For tiny indented areas you can use a little one in a die grinder. Wire brush in drill should do, but is a lot less aggressive.

Hammerite is terrible for pinholing, and not whats wanted for rustproofing.

Finally yes, the other side should get treated if possible, in whatever effective way you can.

Yes, for best result. Cheap silverline ones are fine. I'd still prefer an angle grinder, but it should work.

no, they last ages

Just tough gloves, indirect vent goggles. Tough footwear & face shield optional.

NT

Reply to
Tabby

Once you've got rust beneath the car, you are better off abandoning attempts to remove it and painting over.

Except for the parts you can see (around the edges of the wheel arches etc, which should be painted, if you can), you are better off cleaning as much of the dirt and rust as you reasonably can (high pressure hose, wire brush etc), and when it is thoroughly dry (use hot air gun or hair dyer if necessary), spray with Waxoyl (or similar). Several thinned coats are better than on thick one. In narrow nooks and crannies, spray with WD40 first.

Don't worry too much about getting absolutely all the dirt off. Dried-on dirt soaked and impregnated with Waxoyl is a pretty good anti-rust protection.

In places where the coating will get a good blasting from road grit and stones, you could finishing off with your own mixture of Waxoyl and underseal. [This sticks better than trying to underseal over a Waxoyled surface.]

Finally, don't forget to top up the Waxoyl spray every six months or so.

Reply to
Ian Jackson

First, check if you have water ingress into the boot (trunk if in USA!). Check the behind any lining at the back of the wheel arches for pools of water - sunroof drain popped out of hole, electric aerial drain popped out of hole, other leak (can need a hose to find it).

Second, realise you can not solve this except by serious application of new metal, but you can slow it down to something which is controlled for about 3-4-5yrs depending on how severe it is. Some cars do however have a problem in the wheel arch area - a weld in the wrong place can let moisture in to a seam, a seam may have the weatherproofing which has failed.

The best way to remove rust without removing metal is to use a 3M Clean n Strip disc. These come in black or purple (XT), the latter is simply a faster version. You can get a version which fits into a cordless drill, or into an angle grinder. To be honest they are so fast and powerful that an angle grinder is quite unnecessary - even a sub 12V cordless drill with a Clean-n-Strip disc will cut through paint, primer/galvanising, rust and clean it to a surprisingly bright finish and get into the pores. It will not get deep into the "worm hole pores", but it will shift the mill-scale leaving pitting.

Then you really want something electrochemical to prevent rust - sadly most cars do not have galvanised wheel arches, those that do tend to have very limited micron depth which erodes pretty easily. The problem is, the more zinc in the treatment a) the more expensive b) the heavier the can c) the more difficult to get cellulose paint to stick to it! So generally go for the highest zinc content paint you can, you then need a primer on top which permits car spray paint to stick to it (galvanising metal primer). Car trailer people use Zinga or Galvafroid, but that needs an alkyd paint (IIRC) on top or a galvanising metal primer which is typically applied with a brush. Pretty it is not, but it is very effective at slowing down corrosion even from the other side (as it should be, I think 250ml of Galvafroid is about =A320 these days and weighs like a lump of lead likewise).

The best solution would be a 2pk zinc loaded epoxy mastic, but they are expensive. Colleague used it on a known atrocious for rust Merc estate which was hammered (literally) as a "wheelbarrow" in place of a van, because he wanted a decent automatic. It worked very well, but was very expensive - or would have been, he actually handles industrial coatings and thus it was little more than a sample to his supplier.

Wire brush is a lot of noise and slow, 3M clean-n-strip is very quick and extremely effective. There is a "Roloc" version which has a small reverse-thread "stick" in the middle rather than a proper shaft/spindle, it requires a "Roloc" adapter which adds to the cost. A cordless drill is plenty powerful (you are not stripping an entire car).

Rust is a worm, it travels as dark patches under paint - but with a good very high content zinc primer you can actually slow it down. You can not stop it, but it is nice to strip a bit off you did 1-2yrs ago and find the progression is minimal, then 4yrs later you find the really bad bit has travelled a bit bigger - but 4yrs is a long time. Some cars are notorious which requires fresh metal and that requires careful practice with a MIG because car sheet metal is very thin (you tack it and let the metal cool since you are fighting erosion).

Frost Automotive do various solutions (they carry the 3M Clean n Strip, but I can not remember which is the cordless drill "pad on a spindle fit-n-go" part number). They do various primers. POR-15 is a favourite anti-rust, but you can not weld metal after using it and frankly since you can only put it on one side of the steel which is rusting from the other side it seems pointless. You need an electrochemical solution from experience and comparing just about everything on the market.

Reply to
js.b1

I think that's OK... I haven't seen any evidence of it (eg car easily steams up inside).

Yes, it's all about control. I realise it's a losing battle eventually.

Are they really that much better than the 'wire brush on a drill shank'? The latter I can buy cheaply locally.

Thanks, useful to know. As this is only the exterior edges of the wheel arches and a few scratches on panels, is this really worth doing? Water+mud is more likely to collect inside. If I underseal the insides I can delay that, but I think it'll still be the weak spot.

I probably have 100-200cm2 to paint, so this isn't a big job. The rest is underseal time.

Theo

Reply to
Theo Markettos

Thanks, that's really useful. So you'd suggest separate coats of penetrating light WD40 or Waxoyl, and then mixed Waxoyl+underseal? I have areas of failing underseal (coming off in lumps) - is it worth pulling this off (might be a bit like peeling an orange - get more than you bargained for) or slapping penetrating stuff on it and then underseal mix on top?

I don't have spraying equipment (unless I buy a hundred garden sprayers or expensive aerosol cans) - is this something that can be done adequately with a brush?

Theo

Reply to
Theo Markettos

3M clean-n-strip remove less metal than a wire brush. So if your application is trying to prolong life (say a classic car) then it is particularly attractive.

If you have rust coming through around the wheel arches it is because the factory applied seal between the two panels has failed, water & salt (winter) has penetrated and once in there is little you can do apart from treat the effect not the cause. Some cars have more than two panels in the area due to layering of steel.

Scrape off (heatgun?) underseal around where it has peeled to ensure water is not getting underneath.

Remember standard automotive spray primer (grey, yellow) is in fact porous. A near 99% zinc primer is the only way to get electrochemical protection, so anything less is somewhat marketing.

Reply to
js.b1

Oops, forgot the other reason for clean-n-strip. Firstly they remove less metal, but secondly the abrasive particle size will get into the rust pores & pinholes to remove millscale and rust much more effectively and they leave a very polished surface.

If you are applying an extremely high content zinc coating this is important as you really need a Sa2.5 finish (walnut/plastic blasting), but when done it will electrochemically counter corrosion particularly "pin hole progression". Car metal that is not zinc protected will pinhole extremely easily and once it does the perforation spreads very rapidly indeed, it is a down of the very thin yet high strength steel alloys used.

Reply to
js.b1

Exactly! You could end up by creating a lot of essentially unnecessary work by removing more of the original underseal than you need to.

Yes. As long as the underseal is generally adhering, it's probably best to leave most of it in place, and try and squirt plenty of WD40 or well thinned-down Waxoyl underneath it. Then go over with the Waxoyl-underseal mixture (again, trying to work it into gaps etc). It will remain gungey for some time, but eventually it will harden to a tacky, rubbery layer. Use something like white spirit as the thinner (both for the underseal and, if necessary, for the Waxoyl).

Why would you need 'a hundred garden sprayers'? I have used one large-ish 8 litre pump-up type - but you need to flush it out well afterwards - and finally with warm water and washing-up liquid. The white spirit etc can - and does - knacker the rubber seals. Alternatively, use a small 'hand-held' one (1 litre or so) - usually obtainable from pound shops, Homebase, B&Q etc. But if the Waxoyl proves too thick to spray, by all means use a brush.

[Actually, Waxoyl used to sell a sprayer which looked very similar to a bicycle pump. It did work, but it was rather tedious having to keep sucking up the Waxoyl before each squirt. Of course, you could try a real bicycle pump!]
Reply to
Ian Jackson

I don't know - most times I've seen that, it's either coming through from the reverse side, or via the join between inner and outer wheelarch - and it follows the iceberg principle, where there's always ten times more than you can actually see :-(

Yep. You can skim-coat it with filler, and you can get thicker primer paints that are designed to be sandable and take up some of the slack.

That of find a very large sacrificial anode, PSU, and bath ;-)

Problem I found with steel brushes were that they took away as much good metal as they did rust and paint. Brass is probably better - or go with some kind of sand-blasting (if you have access to a compressor you can DIY)

I think I used Hammerite the last time I messed with anything like this. Then a few coats of thinner primer, then a few coats of top-coat. Mind you, I was welding in new metal too because some bits were just too far gone to mess with filler.

I had a huge cannister of waxoyl which came with a pump and spray attachment, and that worked well. Fiendishly messy stuff, but it did the job.

Do your best to get rid of any broken bits that are flaking - the waxoyl's going to stick to them, and they're going to eventually fall off, leaving you with unprotected metal.

Are you working indoors or out? If outdoors, well... it's not going to rust into oblivion in half a year - I think I'd be tempted to just say sod it and deal with it next year. If indoors though, invest in a heater...

cheers

Jules

Reply to
Jules Richardson

If underseal is peeling off, the rust will have got some way past the edges of the loose bits. I remove the loose bits then some way round the edges with a hot air gun. Then sand down to bright steel, apply a zinc rich primer, then underseal.

Waxoyl is far from the best of those sort of things. Have a look at the Dinitrol range.

Reply to
Dave Plowman (News)

In message , "Dave Plowman (News)" writes

That's fine if there are only a few, isolated areas of rust. When there's a lot of it, it's usually less soul-destroying to abandon attempts to do a 'restoration' job, and concentrate more on damage limitation, as I have described. If the rust hasn't really got a hold, it's often better to leave it in place. The WD40, Waxoyl and Dinitrol (which I haven't used myself) will soak into it and slow its progress - especially if you can break its surface first (by scraping or using a wire brush).

As I've said, I've never tried Dinitrol. I always wondered what it was like. At my time of life, I no longer drive the rust-buckets we used to have to make do with in the past. Hopefully, those 'happy hours' of hacking at the underside of cars are over!

Reply to
Ian Jackson

Practical Classics did a basic set of tests on all the common waxes.

IIRC, they cut bits out of an old but good painted panel, scraped some of the paint off, applied the wax, sprayed them with a salt solution and left them outside.

Reply to
Dave Plowman (News)

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