How Do I Choose a Rust-buster?
Rust, tinworm, rot – whatever you want to call it – is ferrous oxide. It forms on iron and its common derivative steel, attacking and weakening. The conditions that allow its formation rely upon the presence of water, air and electrolytes such as salt or acids in water or air.
Our constant challenge is to halt its onset by coating iron and steel with a skin or protectant to seal them from such conditions. Most rust-busting products are based on phosphoric acid. This converts ferrous oxide into ferrous phosphate, halting the process. Primers and barriers such as paint, zinc, galvanisation and waxes create a further line of defence. Effective use of treatment products requires a realistic approach. No rust treatment product can make rotten metal solid.
ROTARY WIRE BRUSHING
This was certainly a quick and effective way of removing rust, and much easier than ‘manual’ wire brushing. We had two types of wire brush to test, and found that we got better results with the flatter disc-shaped one rather than the cup-shaped angle grinder version.
Even so, we suspect it could be quite harsh on the metal. As careful as we were trying to be, a couple of nasty looking deeper scratches still appeared on the surface. As you’d expect, though, being metal it lasts much longer than the other drill-mounted stripping disc tested here.
This would be a good choice for medium-sized areas, and you could do a whole car relatively easily.
These stripping discs came highly recommended by our snapper, Matt. Sure enough, they were quick, easy and gave a much smoother finish than the drillmounted wire brushes we tried. Even being fairly harsh with it, there were no nasty scratches left behind and the metalwork came up beautifully.
We were only testing small areas of rust, though, and even then the disc was starting to wear away quickly. The catalogue claims you can do a whole car with eight discs, but we’re not sure about that. Maybe if you kept the drill speed down it would last a bit longer.
Concerns about their durability aside, we’d recommend these highly. They were easy to use and, more importantly, left a great finish.
AIR GUN & GRID
This set-up is meant for small areas of rust, such as stone chips, or even wooden frames. On tiny areas this proved to be absolutely brilliant. The surface looked more like it had been painted. It was very fiddly to use and got messy when we didn’t quite get it right.
The idea is to get the nozzle squarely on to the area you’re treating using the correct shape nozzle for curved or flat areas, which required practice on the more difficult curves of the Herald’s bodywork.
You need a compressor – and probably a better one than we had. That said, if you’ve only got a small area to do, the results can be astonishing.
Coming in a spray can, this was really easy to use. It went on quickly and cleanly, and we were able to achieve good, even coverage over the test area. It needed a couple of coats to be able to do its thing, but once left it seemed to work well.
The rust looked like it had been ‘converted’ to a hard black substance, which should then provide protection against future corrosion. It should be easy to work with as well because it dried to a hard, smooth finish. We’d recommend this.
POR-15 METAL PREP
Metal Prep was one of the most time- consuming of the treatments we tried. You need to keep the surface wet, meaning you have to keep applying it over and over again. It would certainly take a lot of time and effort to get the result shown in the catalogue.
It worked well though, and left a nice-looking surface that wasn’t too rough. We applied it to the metal using the spray nozzle, but would guess that immersion in the liquid would be the best method and give better results than the way we were using it.
It leaves the metal coated with zinc phosphate and is ideal prior to etch primer use.
GRANVILLE RUST CONVERTER
This convertor is heralded as used by the MoD and NATO. It looks like yoghurt, has a very similar texture when brushed on and requires two coats to work effectively. A rusted surface such as our test metal is necessary for it to ‘key’ and take hold. Once dry, it forma tough gloss black coat, which can then be primed and painted with topcoats of your choice. It’s designed to be left on, not wiped or wire brushed off. Being heavy duty, it’s best suited to areas hidden on your classic – chassis, suspension components and the like. Patience is the key to using this one. Effective as a barrier. Use in vulnerable areas.
Read this article in the October 2007 issue of Classics Monthly (p77-78).