When rust is discovered on thin body metal or even on sturdy chassis or suspension components there are two options for dealing with it. Preferable is the complete removal of all traces of rust from the surface of the metal, followed by primering and top-coating. This can be a time-consuming process, however, and many people prefer to utilise rust arresting products. Sometimes, the body panel metal can be so badly rusted and thin that completely removing the rust might result in a hole. In such circumstances a good rust arresting product can help to prolong the life of the metal, provided that it is not a structurally important panel.The car accessory market usually offers a wide range of chemical treatments which are all 'guaranteed' to arrest existing rust and ensure that the metal never rusts again. Not all appear to actually work in the experience of the author and also according to various published reports of independent testing. Rather than list the many products which do not reportedly work, the two which in the author's experience do work and which he uses are Bondaglass Gloss 'Bonda Prima' and Dinitrol RC800.Unlike many other products, Bonda Prima is not claimed to chemically alter the composition of rust. The manufacturers state that it works by infiltrating and encapsulating rust particles in a resin. Dinitrol RC800 converts rust into an inert organic compound which can be primed. Both certainly work.In order to work properly, rust arresters should be applied only to flake-free, grease-free and dry surfaces, which should ideally have no more than a thin coating of corrosion.It is useless, incidentally, to use any rust arresting primer on metal which is to be filled. If you are straightening out a dent, for instance, then you have to remove all traces of rust before applying the filler straight onto clean metal, because if you were to apply a rust-resistant primer first then the filler would adhere strongly only to the primer, which does not itself possess sufficient adhesion to the metal, and both filler and paint will drop off in next to no time. If you apply filler over rusted metal, the rust will rapidly spread underneath the filler, which will eventually drop out.To arrest rust, you should begin by thoroughly cleaning and de-greasing the section in question. When it has dried then it may be firstly wire-brushed and finally rubbed with emery cloth or paper in order to remove any loose rust and to key the surface. Follow the instructions with whichever product you choose to the letter. in the case of Dinitrol RC800. this entails merely painting on one or more coats (12 hours between coats) and then applying any primer paint. The work should be carried out in a warm, dust-free and dry building if possible; otherwise on a hot and dry day outside. Bonda Prima is available in a spray can or a tin for brushing or spraying with a compressor. After treatment, cellulose should be applied either within 6 to 24 hours or after seven days; other paints may be applied after four hours.Areas which can really benefit from rust arresting maintenance are those body panels on the underside of the car, such as the heater channel closing panels and the floorpans. If underseal on such panels shows any signs of lifting then the following can greatly increase their life-span (assuming that they have not rusted right through).Firstly, all traces of old underseal and paint have to be removed. The easiest way in which to achieve this is to scrape away the undersea] and then use paraffin and a rag to remove the remnants. You can use an electric drill (or an air drill powered by a compressor) fitted with one of a selection of wire brushes and 'flap wheels' or, alternatively, an angle grinder fitted with a cup brush.Beware the lengths of wire which become detached from the cup (which rotates at 10,000 or more rpm) and fly off at high speed – but these will tend to rip away filaments of underseal which stick to whatever they hit. Protective clothing, especially goggles, must be worn to avoid personal injury from flying rust flakes and the aforementioned lengths of wire from cup brushes. If the panel being treated is anywhere near the petrol tank then this should firstly be removed.Next, as much rust as possible should be removed using emery cloth or paper (to work right into corners) in addition to the drill and wire brushes and flap wheels. No more than a very thin coating of rust should remain.. Apply the rust arrester, followed by a second coat and a topcoat at the recommended intervals. Underseal may then be re-applied if desired to finish the job.