Rust treatments: what to use and when?!

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Joined: Mon 29 Dec, 2014 14:23
Posts: 26

  Z3 roadster 3.0i

Rust treatments: what to use and when?!

Post by RobTFC » Sun 14 Feb, 2016 19:36


I'm currently in the process of doing work on my '97 2.8 Z3. This involves curing the body panel rust which I've side-stepped by simply buying new panels however I've noticed in the engine bay there are various spots of surface rust I'd like to get sorted.

For example;
- Some blebs on the underside of the bonnet (a bit around one or two of the openings on the inner skin, and a little on the inside of one side of the bonnet.
- The front panel (part number 41138398682) has a bunch of surface rust on the top area of the panel facing the bonnet.
- Little blemishes in areas such as under the water bottle where things have rubbed over the years, taking away the odd piece of thin paint and letting the rot get in.

None of the areas are big enough to spray (unless I were to tackle the whole front panel as a single piece), they will all likely be touched up using a very small brush. As the areas are all small and in the engine bay it does not have to look perfect.

I've done some exploring and in all cases I can rub the rust back to metal pretty easily as none of it goes particularly deep. What I'd like to do is get rid of the rust by scraping/brushing etc., treat with a product, or set of products then repaint the affected areas using the matching BMW paint touch up kit.

My question however is what does anyone recommend to do this? There seem to be a variety of products, some to paint directly onto the rust, others to prime, some prime and protect, some are inhibitors, some simply prevent etc. Then there are so many manufacturers of these products it gets rather confusing!

Could anyone point me in the right direction for recommended products/manufacturers and any tips on application?

Many thanks!

Joined: Thu 02 Jul, 2015 21:07
Posts: 61

  Z3 roadster 2.8

Re: Rust treatments: what to use and when?!

Post by 5harp3y » Wed 17 Feb, 2016 16:44

i've heard great things about the bilt hamber dynax range. their website gives you a great run down of what to use and where

Joined: Sat 19 Nov, 2011 18:35
Posts: 2126

  Z3 roadster 1.9

Re: Rust treatments: what to use and when?!

Post by Del » Wed 17 Feb, 2016 23:32

For rusty paint chips I use Fertan rust treatment – recommended to me by the Alfa Romeo owners club – and they know about rust. On top I put a zinc primer and then the top coat touch up.

For underside parts where you need a paint/rust converter to apply straight to a dry/clean rusted area, we use Por 15. This stuff is utterly brilliant and sets like steel. It is so strong that one pot we had got a bit messy around the rim of the pot and it stuck to the lid so hard that when trying to remove the lid some months later, it actually ripped the pot sidewalls away with the lid. I am aware that a BMW specialist restorer in my area uses Por 15 also.

Joined: Mon 29 Dec, 2014 14:23
Posts: 26

  Z3 roadster 3.0i

Re: Rust treatments: what to use and when?!

Post by RobTFC » Fri 19 Feb, 2016 12:25

Thanks for the posts - I've decided to give Fertan a go as I like the sound of the fact it actually loosens and kills the rust rather than just covering over it.

My plan now is to;

- Lightly brush affected area to loosen up rust.
- Treat with Fertan
- Apply zinc primer
- Touch up with topcoat.

The only pieces missing are how to smooth/polish the metal off once the rust has been removed and how to match the engine bay colour (which is body colour but only the non-metallic base layer with no top layer or clear coat). For the former would anyone recommend those polishing bits you an get for a standard drill?

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