Rust prevention and treatment by removing or converting

Rust is one of the biggest killers of classic cars, it is usually easier and cheaper to replace or repair a worn out engine for example but a worn out chassis or body shell through rust can be very expensive to put right due to the time involved to put it right correctly. Below is what happens when rust wins!

Rusty Stag

It is therefore better to prevent your classic rusting in the first place the following are common sense tips to slow down the onset of rust.

  • Keep your car clean and wash any salt deposits from the car in the winter.
  • Wash the underside of your car or use automatic washers with underside spray. This is most important during the winter when salt is applied to the roads.
  • Wax the body of your car.
  • If the car is not garaged use a car cover that breaths so moisture from the ground isn’t trapped under your car.
  • Fix chips in your paint before your car has a chance to rust.
  • Remove mud and other debris from your wheels and wheel wells/arches.
  • Make sure your drain holes in your car are free of obstructions. This is a major cause of rusted doors and sunroofs.
  • Use some anti rust products in the box sections and chassis rails so the car does not rust from the inside out. (see below for more information).
  • Protect the underside of your car by wax oiling every year (see below for more information).


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There are many products on the market for rust prevention in different areas on the car most of these are waxy type anti rust solutions that are sprayed or brushed onto the underside of the car, and equally into its many box sections. These can provide a very robust means of keeping damp at bay, although they do need repeat applications at least once a year especially in areas such as wheel arches that get repeated blasting from road spray and grime. The old loose product should be brushed away first and any corrosion found treated to stop it progressing further before another coat is put on.Waxoyl is probably one of the better known and available products, and one that I've used to good effect in the past on my MGB GT. There are plenty of other products from companies such as Commer and Dinitrol. I used the Dinitrol cavity wax on both my MGB inner sills and chassis rails as well as coating the inside of the repaired chassis of my Triumph Spitfire.

Finding rust to treat!

Finding rust in classics usually is not a problem and some are worse than others for susceptibility although they all were not protected as much as modern cars are when they left the factory. Some rust and rot spots are specific to the model and therefore cannot be shown here and dedicated buyers guide for the model should be locked at for problem areas. There are however a number of areas to check for rust on just about every classic these being front wings, sills, rear arches, spring hangers (if fitted), suspension mounts, A posts, front and rear valance and floors. In general if you are buying a car you should go round one panel at a time and check for signs of rust bubbling through and any bodges or fiberglass covering up any problems should be treated with caution as rust on the outside is usually 100 times worse on the inside. Cost to repair or replace is also a consideration, if you have well supported model like an MGB then just about all the panels are available through the Motor Heritage and even complete body shells if the one you are working on is too far gone. If therefore you find rust in a front wing then it might be easier, cheaper and a better long term fix to replace the whole wing with a new reproduction part rather than to patch. If you replace the whole wing then the old one will be completely be removed allowing access behind the wing to carry out any repairs to the inner wings and then properly protect the hidden areas with wax so making the repair a much better long term solution.
Sills and floor pans can take a real battering, and on most cars they are structural. The Triumph Spitfire is a classic example of a car which can suffer more than most if the sills are shot. Despite having a separate chassis, the Spitfire still relies on the body shell for structural strength, especially given that's its a convertible and doesn't have a roof to provide structural rigidity. Rare is the Spitfire that hasn't need sill and floor pan welding by now, given that the youngest is over 20 years old now, and the giveaway that all is not well is when the doors start to droop, or when the doors are lifted upon slightly, the whole A post moves in unison with the door (don't confuse movement here with worn door hinges however). My Spitfire body has had major work carried out before but even so the sills and floor were completely rotten and a full restoration is in progress click here to go to the Spitfire restoration pages

The pictures below show what happens if a convertible car is not well rust protected.

Inner Sill Shot   Sill Shot

Treating the Rust

With my Spitfire in a lot of cases there is no alternative but to cut out the rusty metal and replace with either complete new panels or at least new metal. Rust converters are solutions or primers designed to be applied directly to a rusty surface to convert residual rust on steel surfaces to harmless and adherent chemical compounds. Unlike the standard grind, prime, and paint regime, the user does not have to bring the surface down to bare metal. These in turn are able to develop a protective film (usually phosphates) on the metal surface that protect against rust. The chemical mode of action of rust converters is the conversion of porous and loose iron compounds to sparingly soluble adherent compounds. The most frequently used formulations are based on phosphoric acid which cause the rust to be converted to firmly adhering iron phosphate layers. In certain areas of the Spitfire I have used this method by removing the majority of the loose surface rust then using a rust converter so that the last bit of rust is removed before priming.

There are products called rust encapsulates which will stabile the rust and prevent it from getting worse. These products are used where the rust cannot be removed (by cutting out a panel).

When welding in new panels or patches it is best to use a high zinc weld through primer, this allows the areas that you normally cannot get to have a coat of a high zinc paint. Some might be burnt off while welding but it is better to try and coat as much metal as possible. Seams should also be painted with a high zinc paint and seam sealed, seam sealer draws out any moisture as it dries and then forms a flexible cover over the seams preventing moisture from getting in.

Once the you car has been seam sealed then the vulnerable areas such as wheel arches and underside of the car can be sprayed with stone chip which is a rubberized paint which remains flexible so that if stones, and debrie is thrown up it should not be penetrated and the stones bounce off. The final defense for the underside is to paint or spray with wax oil which although is a messy job it really helps in the fight against corrosion and can be checked each year and "topped" up each year.

The paint on a car although looks good really is there to protect the metalwork so it is important to keep the car well polished and waxed. Any stone chips should be repaired as soon as possible to keep out moisture and keep the car looking good.

Most classics will have either a separate chassis or will have chassis rails which need to be filled with cavity wax. A lot of these products have long tube applicators so that they can be fed into holes in the chassis or sills and then sprayed down the length as the tube is withdrawn. As said above I have used these products on both the MG and the Triumph and found them extremely easy to use and gives good protection.

Classics will generally have a lot of chrome fitted to them, these item include bumpers, trim and windscreen surrounds. In some cases such as the MGB bumpers replacement items are availed at a very low cost. Some people say that the quality of these items is not very good however I have fitted to my MGB new front and rear bumpers to replace the badly pitted items on the car. These bumpers have been on the car for 6 years and they still look very good and it is not as if the car only goes out in the dry, the car is used all year round and in all weathers. I wish the same was true for the Spitfire which does not have bumpers available at a low price. These are only available as exchange items and cost about 350 pounds each! which is why most spitfires run around with old bumpers fitted.
It is important however to keep the chrome clean and polished, if you use the chrome cleaners these will remove a very small amount of chrome every time you clean and do not offer any protection. On the MGB I always clean the bumpers and the rest of the chrome then use the car polish I use for the body work to put some protection on the chrome. Some owners who lay their cars up over the winter coat the chrome in polish but do not polish it off.




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| Updated 28 Dec-2007 |