I am looking for a rust converter/paint system for a few rust spots on my car.
What recommendations are there from the brains trust??
Thanks in advance.
rust conversion is basically the action of phosphoric acid on iron oxide. I forget my chemistry but I think it converts iron oxide into iron phosphate. This acts as an under coat.
In practice it isn't always that simple.
Ranex is the product I've used, it's diluted phosphoric acid ready to paint straight on.
It certainly works, especially where the whole article is evenly covered with rust.
But spots are a problem, you don't want to leave the acid on paint work for very long, so a quick wipe off is essential. You also don't want to leave any unreacted acid around before painting. If there's any bare steel around, and you wash the acid off, the steel can start rusting before you paint.
So I've had mixed success over the years, and earlier jobs have been better than later. I'm not sure if the product has gone off a bit over the years.
I hand sand the rust away then i use the 2 in 1 converter primer from SCA (super cheap autos brand) itll turn the paint a gross brown and the rust a nice black. Then i just paint it with cheapest auto spray paint i can find then spray paint a clear coat on it. My cars paintjob looks like ****n garbage but you can strike matches off it but i dont care i only care about the rust.
^^^ +1 for both of the above but Fertan is a far superior product (not phosphoric acid based)
After killing rust and good wash, how far do you want to go? Any paint system that is durable and will keep the water and O2 away means it can't rust again. But obviously quality 2 pack poison is far better than rattle cans..
There phosphoric and tannic acid based products. Some of what I have read from Google searches suggests a mixture of both.
When either or both are used there is not 100% penetration and there is residual acid that needs to be washed off. So no matter how stable the ferric phosphate or ferric tannin resultant is, it needs to be sealed. I was told that phosphoric can only take oil based overcoats whereas tannic can take water or oil based overcoats.
I am leaning towards tannic but I will have a look at the SCA 2 in 1. Like vodka I am more concerned about rust than paint.
The spots I am doing are about 50 cent size.
Any panel beaters here who can tell me what they do and use? Most panel beaters will not do rust repairs these days, only replace panels.
I just apply fish oil a few times. Penetrates well and stops the leaks around the windscreen too. You can even paint over it once it's dried, not that I'd ever bother. Only takes a few minutes and I reapply every couple of years. Ends up doing a better job than most rust repairs I've seen that seem to always return, worse than the time before because they are often rusting under the repair paint, getting worse each time.
I've been using corrosionx on my motorhome chassis. Seems to do a good job but I don't think you can paint over it. US navy uses it on there ships, so I think they would use a quality product.
Thanks for all replies.
As it is for rust spots on the body of my car it appears best to use the three step process as described in the POR 15 vid. POR 15 has the best reviews but the method could be used with other brands.
After removing rust with sanding disk or similar:-
1. Clean with wax and grease remover, rinse off and dry.
2. Acid cure with phosphoric, rinse off and dry.
3. Seal the metal with appropriate paint.
Follow up with primer and top coat.
"every cloud has a silver lining" kinda story...
I am pretty sure rust will never be a problem I need to worry about 
[2 x 1 litre cans of Ballistol split open in the boot of my car] 
So what I said Cisco. Kill the rust, paint it right.
Careful of POR15 its an amazing product but some is designed for underbody only (light degrades it)
The POR 15 looks to be a quality product but a couple of vids on Youtube show how it will peel off in sheets.
It is still a toss up between phosphoric and tannic acid cures. Phosphoric seems to need a bare metal cure and then clean off slight residue then seal coat (epoxy or etch primer).
Tannic needs clean rust surface to cure then an etch primer. White Knight products look good and am leaning that way.
The critical point I think is the bond of the first primer coat.
Cant yet get a definitive answer from a panel beater.
Select to expand quotecisco said..
The POR 15 looks to be a quality product but a couple of vids on Youtube show how it will peel off in sheets.
It is still a toss up between phosphoric and tannic acid cures. Phosphoric seems to need a bare metal cure and then clean off slight residue then seal coat (epoxy or etch primer).
Tannic needs clean rust surface to cure then an etch primer. White Knight products look good and am leaning that way.
The critical point I think is the bond of the first primer coat.
Cant yet get a definitive answer from a panel beater.
Put Por15 on the inside of the hull of my steel Adam's 40 after sand blasting it. The only section that peeled at a later date was the bilge sump. But the steel underneath was still in pristine condition, so I cleaned it up and put on another couple of coats of Por15. Never had another problem. I think there may have been some oil residue still in the steel after the first time I sand blasted it, which resulted in the Por15 not adhering properly. Good stuff.
Previously used fish oil and wasn't worried about appearance 
Wife's car had a few spots under bonnet and sanded then used CRC rust converter which leaves the surface with a black primer finish.
Interesting that it only left black primer on the rust spots and not on area I coated
No need for rust converters, mate now has 2 laser rust removal machines. A big one and a littler one. ??
theres a more expensive product than the phosphoric acid based products.
Galmet ironize. www.itwpf.com.au/galmet/galmet-ironize/
It does the same sort of thing, (changes it to a black shiny thing) but does not use acid. Its water based. check it out. good for things where u don't want to use acid. if u get it doesn't last in the bottle forever goes hard, got to move bottle/ shake occasionally
My old man fixed up an old tractor to tow our boat down the beach to launch.
He used this stuff
www.hammerite.com.au
Brilliant never saw any rust ever even though the tractor was often submerged in salty water
Ironize and Hammerite both sound good being water based and non acidic but Hammerite seems not to be designed to be overcoated.
This feronite rust primer is great. Made locally for marine use. I have used on metal roofing, trailers tools etc. I just recoat if you don't want to Color match
boatcraft.com.au/Shop/index.php?main_page=index&cPath=162_163
