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MG MGB Technical - Rust spots

Hi,

Any advice on this one?

I have one car that has been resprayed recently.

When I sanded down one wing, it showed up a of rust spots; about, half a dozen or so. I got to bare metal around them, but they were deeper (about 1mm deep) and the largest was up to 3/4mm wide.

I wire brushed, poked about inside the holes with needles a few times; used anti rust treatments - e.g. phosphoric acid gels. Primed with anti rust primers etc. and painted. Now, two years later, I can see the signs of where they were; coming up through the paint. Doh!

Any advice on how to get rid using uk materials. By the way, I won't use hammerite rustbeater as it causes big problems with the covering coats of paint.

Ta,

Iwan
IA Jones

Did you mean three-quarters of a mm wide? or 3 to 4 mm?

Really you need to remove metal down past any corrosion, to be sure you have got it all. Scratching at it may well move the loose stuff but not the initial traces that further corrosion will come from. And if any actual corrosion is left behind, any treatment may well not get underneath it. You need to grind it out with a small stone, maybe even a dentist's burr. Then back-fill before paint.

With the metal used in the 70s corrosion could start from within the steel itself if it wasn't molten at a high enough temperature to make all the impurities float to the surface.
paulh4

Hi Paul, yep the biggest one was about 3-4mm in width, but not that deep if I remember. Heigh ho! Not really that obvious at the moment, I'll leave it for now and tackle it in the Spring.

I have been told, by a friend that he had much the same once on his Triumph and I should try to do a shallow form of lead loading, almost soldering the lead to the rust spot. (Then sanding this down obviously)

Ah, yes. As a young boy I just about remember the problems with bad steel in the seventies. Wasn't it worse with Russian steel and Fiats - or some other Italian marque?

Ta,

Iwan
IA Jones

I almost mentioned lead-loading, used on most MGB for filling some of the rear seams! Needs skill to get just the right amount of heat to make it plastic, but not melt, and plumber's lead not tin-man's i.e. cored electrical solder.

Oh yes, 'Polski' Fiats - terrible reputation! In those days what Russian cars there were had bodies made from a type of plastic :o)
paulh4

Not only Russian Fiats had poor steel being used. 1972 Ford Ranchero purchased new and never left florida.
The cowl sheetmetal at bottom of windscreen rusted through along withthe floorpan under the driver's seat.
Ford however offered a $2000.00 credit on trade-in for new car.
The cowl sheet metal was coated with a type of galvanizing.Apparently it did not work.
Sandy
Sanders

Polski Fiats were made in Poland, I believe.

Italian Fiats were pretty bad, along with Lancias.

Remember the Lancia Beta recall/buy-back and crushing scheme?

https://en.wikipedia.org/wiki/Lancia_Beta#Legacy
Dave O'Neill 2

Iwan

Zinga - then normal primer.

Roger
Roger Walker

iwan

i am at the juncture as you were back then....

the way i see it is that unless one cuts out/replaces every panel with grot there is no real prevention method and even new steel is not immune. of course it's a balancing act of cost vs risk....

i took my B to MGOC workshop a couple of weeks ago for a discussion on respray. new bonnet, new tailgate, new wings front and rear, new doors ...was the start of their minimum standards....

so as a ballpark the estimate was £10k+ (excl new tailgate and engine bay!) . silly money for a B but i guess if one does the sums that's the cost of time & materials.

so the mortals among us (who might reasonably expect another 40 years from such treatment-but will probably be disappointed) may be better selectively doing what you have done, but in the knowledge that rust may never die...and to fix as it returns.

in the 90's i had a bare metal spray on my sprite. within 4 years rust appeared from places that had previously not appeared rusty.

like you i have been rubbing down to bare metal, using jenolite and epoxy primer. but i fear that after a few years after spraying, the inevitable will happen.

i cannot help wondering if it's best to leave the areas of paint that have not rusted - and just to rub down for a key.

any experience of others taking such approach?

G

Graham Moore

I removed the paint anywhere I could see any rust, ground it out, and treated it with Trustran - a watery black liquid that turns rust blue-black, cleaned off on sound metal where it stays black. I replaced one rear dog-leg that was perforated, and patched a hull under one of the rear lights. It then got a bare-metal respray ... and that was 30 years ago.

A few years after the respray I did have to replace the second dog-leg - knowing what I know now I'd probably replace them anyway as very few people know how to protect the very narrow gap between the back of that panel and the sill, ditto the lower front wings. Other than that the rear hull had to be patched again - I should have cut more out the first time, and one spot has bubbled up near the lower front corner of a door from inside. No other rust. It's not a daily driver of course, much less kept outside, but going on several organised runs each year it's probably got wet more times than its stayed dry, and even been out in snow and salt a couple of times when the Kimber Run used to be in the Peaks early in the season.

Lucky? Maybe. I think the biggest thing is not shutting it away in a garage while it is still wet, and if still a bit damp getting it out as soon as you can to air and fully dry.
paulh4

what's the dog leg paul?
G
Graham Moore

The lower part of the rear wing that covers the sill.
paulh4

This thread was discussed between 06/08/2018 and 18/08/2018

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