The formation of rust, e.g., on iron (Ferrum) is not only encouraged by humid air, but also by CO2 and of course, acidic substances. All of these contain sufficient oxygen to convert Fe into Fe2O3, which has a rather unstable structure. Aluminium, e.g., can handle the process much better, in this case, the oxide forms a solid protective coating.
The reason why rust always forms new layers and that rust-converter has little chance of converting the Fe2O3 into Fe3O4, is probably because of it's loose and porous composition. As a rule, rust-converters try to form a solid layer, however, for this to happen, one must apply and match, exactly the right amount to the corrosion area, which is difficult.
The best protection against rust is still, not to let it happen in the first place, this means keeping the iron material away from air. It's not wthout reason that we import a lot of veteran cars from regions like California, for a long time southern European car manufacturers used less rust protection than those in the northern regoins.
In addition, because of the electro-chemical reaction, one can place a so-called sacrificial metal which is more base in the tension range, near to the iron. For this reason, hot-dip-galvanizing is a very good choice. It is used, above all, in our newer cars. This may be the reason why the self-appointed used-car-checkers now pay much less attention to perforation rusting than before.
Indeed, there's nothing one can do about it. Once the metal has a yellow tinge, this must be removed before a suitable treatment can take place. Even if you buy Hammerite, you will still be required to remove the loose rust before applying it. Now, how does one get rid of the rust thoroughly, if one doesn't want to rely on Hammerite alone? The angle grinder (Flex) is too coarse and also gets too hot. The wire-brush is too weak and neither method can get into all the nooks and crannies.
Not only the veteran car experts swear by sandblasting. However, caution must be exercised and the area should be examined by an expert beforehand, otherwise there may not be much left of the material afterwards or it has a wonderful ripple-structure, which might stabilize, but can hardly be puttied out.
By no means does sandblasting only
function with sand. For badly rusted floor panels there is corundum, which the sanding-disc uses. Apart from synthetic material and glass beads, dry-ice or snow may be used on weak sheet-metal frames, because it works very gently. In all cases, compressed air is the driving force and the users must protect themselves accordingly.
It would not pay to purchase a sandblasting machine for the one-off restoration of a veteran car, particularly as one would possibly need to treat larger areas. There are however, any number of businesses, where for a fee, one can use the equipment. This way one can also save money by doing the work oneself instead of paying an hourly labour charge.
One can ask around in the veteran car scene for tips concerning the best preservation methods. For the outer plating, e.g., the floor panels, Fertan (no intentional advertising) is often recommended. Otherwise, no undersealing is applied, however, regular inspection is carried out. For hollow cavities, hot-wax has proved to be very good. Indeed, it remains questionable whether or not it protects surfaces which are more aggressively attacked. 03/12