Rust proofing - can products be used over painted surfaces?

[Mr Lazy]

I want to rust proof/convert various components. If they were bare metal then I think I would know what to do. Similarly, if they were painted but so badly corroded that the paint was useless then I would remove the paint before applying any products. However, I have many components, such as the rear cross member and rear suspension linkages, that still have a functioning, protecting layer of paint but also have rust showing through. In cases like this, can products such as Bilt and Hamber Hydrate 80 rust converter (which looks pretty good) be applied straight over the top or does all the paint need to be stripped off first? Similarly, I'm not sure if spraying Dynax 50 cavity wax into the rear subframe would be effective if there is already some rust inside.

[1979scotte]

Maybe try a rust converter?
They're supposed to be very good.
Sure somebody can recommend a brand.

[Mr Lazy]

@1979scotte Hydrate 80 is a rust converter, but I've never used anything like this before. To clarify then, Do you think rust converters would be as effective without removing paint beforehand? Or is this the very thing they are designed for?

[Joesson]

@Mr Lazy
I have long understood that preparation is the "key" to all things and that maxim particular applies to protective coatings, paint etc.
If the existing surface is abraded then any applied coating has a greater surface area to adhere too. I believe a rust converter will bond well with rust but likely not so well with a painted surface, but as with all things perhaps best to read the instructions/ ask the manufacturer.
As for Dynax cavity wax efficacy on already rusted areas, I do hoe it does the job as that is what I did a few years back.

[SV-3]

I want to rust proof/convert various components. If they were bare metal then I think I would know what to do. Similarly, if they were painted but so badly corroded that the paint was useless then I would remove the paint before applying any products. However, I have many components, such as the rear cross member and rear suspension linkages, that still have a functioning, protecting layer of paint but also have rust showing through. In cases like this, can products such as Bilt and Hamber Hydrate 80 rust converter (which looks pretty good) be applied straight over the top or does all the paint need to be stripped off first? Similarly, I'm not sure if spraying Dynax 50 cavity wax into the rear subframe would be effective if there is already some rust inside.

From BiltHamber website:
"dynax S50 is a high-performance anti-corrosion wax that provides exceptionally long-lasting protection to steel surfaces. It creeps into welded seams and seals surface defects. dynax S-50 forms a soft, brown, wax-like film that self-heals in the event of disruption. It is also able to arrest existing corrosion and to provide long-term protection to pre-corroded and corrosion-free surfaces."

[Mr Lazy]

@Joesson Good tip about roughing up the surface. I suppose if the rust converter doesn't bond to the paint then it can be assumed that the paint is still doing it's job and preventing corrosion.

@SV-3 I knew I'd read that somewhere before :-D. Good to hear that someone has actually done that though.

[Jay]

Wire wheel then apply the convertor over the top.

You can then coat with two layers of their zinc primer and pick a top coat or just coat the lot with their Dynax UC waxoil.  Or all three which I did lol.

[SV-3]

@Joesson Good tip about roughing up the surface. I suppose if the rust converter doesn't bond to the paint then it can be assumed that the paint is still doing it's job and preventing corrosion.

@SV-3 I knew I'd read that somewhere before :-D. Good to hear that someone has actually done that though.

Just checked through previous posts, and both @Ardent & @Joesson have applied the Dynax.

[Mr Lazy]

Wire wheel then apply the convertor over the top.

You can then coat with two layers of their zinc primer and pick a top coat or just coat the lot with their Dynax UC waxoil.  Or all three which I did lol.

Thanks. I can see that that is the most thorough method. I guess I was living up to my namesake and hoping I could just slap a bit of rust converter over the top of the paint and be done with it.

[abbot]

It's definitely worth doing the proper prep first before applying anything as you will get much better results which will last longer and save you time in the long run by not having to go back over it again in future.

I've used Hammerite Kurust in the past for small areas of rust treatment then painted over that but I haven't seen that mentioned on this forum much.