Workshop Skills: Paint and Protection
Discover the best DIY techniques for painting and rust proofing the bodywork and other parts on your classic car.
Our series on maintenance and servicing moves on to look at the basics of painting and protecting components.
Preparation is in many cases more important than application when it comes to painting and protecting a classic car, or even just a small component that’s fitted to it. There may well be products that promise to cover and protect metalwork with one single coat, but there’s no escaping the fact that if you remove corrosion and key the surface properly, there’s a greater chance of success. Flaky rust and unknown contaminants from previous resprays are some of the problems waiting to threaten fresh paint and ensure it will fall off or react within a few days or weeks.
Choosing the right paint is essential too. For small jobs such as painting a suspension component or a mounting bracket, most of us choose to apply paint from an aerosol can or a tin (applied with a brush), which don’t require mixing with any other chemicals. These types of paint are usually either cellulose or acrylic-based, both of which offer fast drying times without the need to bake them in a warm environment.
If a more hard-wearing finish is required when painting a component, such as on a suspension arm that may become peppered with road dirt and stones, then there are several options. Powder- coating is a popular choice, but requires specialist equipment and while it is very hard, that also means it can be brittle. DIY alternatives include applying a synthetic resin- or enamel-based paint such as Hammerite or Woco Supercote enamel gloss paint. These types of paint are often fast drying and provide a durable gloss finish.
Prep vs Longevity
Deciding on how much time is needed to prepare and paint a surface or component is perhaps best decided by what it will be exposed to and how long it needs to remain intact. Take a dashboard rail inside a car for instance, especially one that will be hidden by the dashboard. It won’t be in
view and won’t be exposed to road dirt or any other means of damaging the surface. Consequently, it may be possible to simply key the surface with abrasive paper and paint over it with a suitable gloss paint.
Where a better standard of finish is required because the component is on show or where it needs to be protected from road dirt and be weather resistant, the preparation is more important. Keying the surface with abrasive paper may be sufficient, but if corrosion is present, it may help to use something more abrasive such as an angle grinder with a flap wheel to remove the old paint and cut back to the bare metal. If surface corrosion still exists, apply a rust inhibitor such as Hammerite Kurust or Woco rust bonding primer, which help to turn any remaining iron oxide into iron tannate and reduce the risk of any further corrosion. The product information on Woco rust bonding primer helps to explain this further, stating: 'Once the product is applied, the special chemicals (chelating agents) contained within the formulation react with the rust cells and form an inert coating that is tightly bonded with the substrate.'
For bare steel, a dedicated metal primer such as Woco Supercote ZP helps to prevent corrosion. As the product information explains: 'This product is designed due to its high zinc metal content to act as a cold galvanising coating. It can be used as an alternative to hot dip galvanise. It prevents oxidisation of steel by sacrificing zinc metal contained within the coating and therefore stopping corrosion of the underlying steel. If the coating is damaged, the zinc will sacrifice itself, stopping rust spreading from the affected area.' Woco Supercote ZP can also be used on steel that has small amounts of surface corrosion (engrained rust).
Once a primer has been applied and left to dry, the next stage is to apply the paint. As mentioned, aerosols and brushing are the most popular DIY methods. Both require good ventilation and it’s always wise to wear a breathing mask. Applying several thin coats is often recommended
to ensure good adhesion and to avoid the risk of the paint running. Even if you want to achieve a thick coating of paint, several thin coats will be more effective and longer lasting than slapping on lots of paint in one go.
In some cases, lacquer can be applied on top to provide a gloss finish and additional protection. This is usually in the form of a clear coat and is available in an aerosol can.
Problems
One of the most annoying problems concerning paint is when the paint reacts. There are several possible causes for this. Chemicals such as silicone-based cleaners and lubricants may be present on the surface despite your sanding back. These can often be removed with a good- quality panel wipe before applying any paint.
If the paint still reacts, even after meticulously cleaning it, there are two choices. The most time- consuming is to strip off all the old paint to a bare metal
surface. Paint strippers can often speed up this process, but you must be confident that all chemical traces have been removed prior to painting and that there are none lurking in a crack or crevice. The second is to apply some form of sealer (also known as a barrier coat) to prevent the old paint reacting with the new. The surface may only need keying with P400- 600 wet-anddry paper before applying the sealer.
Rust proofing
The aim of painting an object on a classic car is often to prevent corrosion, but where the finish is either not important or needs to withstand the abuse of road dirt and water, there are a number of hard-wearing solutions that fall into the category of rust proofing. This level of work can be timeconsuming, and preparation is definitely more involved than application.
Whether you are rust proofing a large part of a classic car, or just one area such as inside a wheelarch, it always helps to remove as many components as possible that could either get in the way or be accidentally painted over. Next, arm yourself with cleaning tools ranging from scrapers and screwdrivers to wire brushes. An angle grinder with an assortment of wire wheels, cups, brushes and abrasive flap wheels can save hours of cleaning, but always wear ear plugs, a full-face mask and a breathing mask because flying debris and dust will get everywhere.
It's unlikely that all traces of rust can be removed from a classic car, no matter how small an area or object you are rust proofing, so applying one of the aforementioned rust inhibitors or primers is essential before any other protection products are used. Make sure this fully dries before the next stage, which may involve more paint, such as a durable stonechip (which can usually be over-painted) or hardwearing enamel, followed by a rubberised underseal (useful for exposed floors, chassis sections and inside wheelarches). Underseal isn’t the prettiest-looking finish, but its rubberised surface can withstand the abuse of stones and other debris. There are some alternatives, such as Witham’s Prolan heavy grade universal general purpose lubricant, which has a clear finish and can be applied with a brush. It’s popular in the agricultural industry where it is applied to farm machinery every couple of years to protect it from corrosion. 'Prolan is a lanolinbased, bio- degradable and extremely tenacious product that has been proven to last for many years,' explains Mick Kenyon at Witham Group, the UK agent for this product. For classic cars, it can be applied in potentially wet areas such as the underside, or even inside a spare wheel well where water may gather. It’s also suitable for moving components that can corrode, such as spring pans. Wax-based rust proofing products can also be used in these areas and some offer a clear finish to avoid spoiling the looks of a painted surface. However, some of these products are cavity waxes that can easily be washed off and are only suitable for spraying inside hidden areas such as chassis legs, so check you have the right product for the intended location – one size rarely fits all.
There are advantages and disadvantages with using each of the various rust proofing products mentioned, so deciding which one to choose isn’t always straightforward. Underseal, for instance, hardens after several years and can thus trap moisture and cause corrosion. Reapplication can sometimes help to keep it supple (it should be reapplied every two years), but it may eventually need to be scraped off so you can start again. Wax-based products usually remain more flexible, but they also tend to be flammable, so if you intend to conduct welding repairs, avoid applying them until afterwards. Some products however, such as XCP Rust Blocker, promise to be non-flammable.
Remember too that hot components such as the engine and exhaust system may cause wax-based rust proofing solutions to become runny and to drain off, leaving areas exposed that are susceptible to corrosion. Even a hot, sunny day can see wax dripping out of the drain channels of a door, so it is best to view application as an annual chore and factor it into your maintenance schedule.