How to use rust converter as part of a car restoration or maintenance project

This is the second in a series of blogs on the four main corrosion-busting steps that typically feature in car restoration or maintenance projects. We have already looked at rust removal, and in this blog we cover rust conversion. In parts three and four we’ll look at using rust proofing paint and rust proofing with wax.


You’re removed the serious rot: what’s next?

We’ll assume that you have removed serious corrosion, either through chemical or mechanical means as described in our rust removal blog. New metal has been welded in where necessary. So now it’s time to deal with any remaining surface corrosion, which can be treated using a rust converter product prior to painting.

First, let’s ask the simple question: when is using a rust converter appropriate? The answer is when you have sound metal, but with surface rust still evident. The metal itself will be strong, but there will be an orange/ginger appearance as evidence that some corrosion is still present on the surface.

If you have had the vehicle blast cleaned or dipped, or if you have used an industrial mechanical tool such as an MBX to remove rust, using a rust converter may not be appropriate. Once you are down to bare metal, or if there are just minimal signs of corrosion showing, there may not be enough oxidisation present for a converter to work.

How to choose a rust converter product

There are several rust converter products on the market, and they all work by converting surface oxides from active Iron Oxide to inert Iron Tannate. So which one should you choose?

One of the main issues is that some products have a higher acid content than others. When residual acid is left in the steel’s pores this can accelerate corrosion. It is therefore important to neutralise the product in line with the manufacturer’s instructions.

Residual acid can be left on the surface after application if you apply the product too thickly, or if the instructions for removing excess product aren’t followed to the letter. Residue can also be left if the conversion process doesn’t happen, for example if the product is applied to areas with no oxidisation.

These potential problems with high acid products are the reason that our own product – Rustbuster FE-123 rust converter – is less acidic. It uses modern rust conversion technology in a more eco-friendly binder containing zinc phosphate, which is known for its performance as a corrosion inhibiter.


Application of rust converter

If it has been some time since you removed loose rust, it is worth doing a final preparation stage before applying FE-123. Brushing off any dirt or dust should be enough, and you can also lightly run over the area with panel wipe if you wish.

Give the bottle of FE-123 a shake and pour a small amount into a container. The product goes a long way, so just decant a very small amount at a time to avoid wasting any. Note that you shouldn’t pour any unused product back into the bottle.

Lightly apply the FE-123 with a paintbrush. FE-123 isn’t designed to be a coating: the idea is to treat the corrosion rather than paint over it. Work the product well into the surface to ensure full coverage. It can also be applied to corroded seams and seals, using a small brush to work it into the crevices.

Remember that FE-123 is a rust converter: it’s not designed to prepare bare metal surfaces. Therefore, be sure to apply only onto areas showing signs of corrosion.

You will know when the product has been effective because the area will convert into a black or deep purple hard and stabilised surface within 15-60 minutes, and should be ready for painting after a couple of hours. There shouldn’t be any need to apply a second coat of FE-123. If you don’t see the reaction as described, please contact Rustbuster for advice.

There is no need to sand or wipe clean the surface before painting (unlike some other products). However, if you see some toffee-coloured areas this is likely to be FE-123 that hasn’t had corrosion to work with. This should be removed with fine sanding prior to painting.

Likewise, in cold conditions you may see a whiteish bloom appear. This can be wiped off with a damp rag and allowed to dry just before painting. This isn’t strictly necessary, but you may prefer an even black/purple colour on the metal prior to painting.

That’s it! Now you are ready for painting, which we will cover in part three of this series soon.

Put FE-123 to the test

Independent testing by ‘Practical Classics’ magazine found that FE-123 not only converted the rust but also left a foundation that could be painted over without neutralising. It earned their ‘best in test’ award, scoring ten out ten points. FE-123 was also awarded ‘best in test’ by Classics Monthly magazine in their long-term test. To find out more, or to place an order, please visit our FE-123 rust converter page.

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