Refinish paint supplier Cromax has issued some very sound and practical advice on paintwork preparation, one of the most important stages of any repair.

Cromax says that to deliver a quality repair, correct body preparation is a key part of the process, together with using the right products and applying them with expertise. Kevin Welling, Training Academy Manager for Axalta Coating Systems has compiled some advice on how to increase productivity by avoiding the common mistakes and pitfalls that can waste time and materials in the prep process.

Know your substrate and keep it clean
The first vital step for refinishers is to know which substrate they are dealing with, such as composite or galvanised steel. For instance, to sand bare aluminium, refinishers should use a fine grade of abrasive to avoid creating deep scratches or generating too much heat, which can distort thinner sections of the panel. It is also important to remember that if the substrate is galvanic, corrosion can occur by cross-contaminating aluminium with steel. This is completely avoidable in a dust- and dirt-free environment, and by using designated tools.

Use the right grade of sand paper
If refinishers do not use the right grade of abrasive paper, it can lead to scratches showing through into the topcoat. The sanding operation should always be carried out in conjunction with a good quality dry guide coat, which should be applied to the repair area before moving to a finer grit abrasive. This enables the refinisher to see any minor defects in the repair area.

Clean and degrease properly
An important aspect of body preparation is full and careful degreasing and appropriate cleaning of the panel before starting the refinishing stage. Refinishers can use Cromax 3608S Prepclean, which eliminates non-water-soluble contaminant, such as wax, polish, tar, silicon and grease, from old finishes. This should then be followed by 3910WB Waterborne Prepclean, which removes all water-soluble contaminants.

Cleaning the vehicle at this stage allows the refinishers to make an accurate assessment of the damage, and also makes refinishing easier and less prone to contamination. Cutting corners at this point can adversely affect the final finish. By regularly changing gloves, and having separate overalls for preparation and for painting, refinishers can achieve a better end-result.

Once the vehicle is at the priming stage refinishers should again use a preparatory cleaner, like 3910WB Prepclean, to eliminate any contaminant that may have settled on the repair area. They should also use a clean tack cloth over the prepared area so that a clean surface is obtained before the application of subsequent undercoats. Cromax recommends 3911WB Final Clean should then be used for the next degreasing steps in the repair process.

Use an etch primer
Many refinishers do not use an etch primer in the refinishing process. This can be a critical error as the etch primer plays a very important role, giving the best possible adhesion between the substrate and the subsequent layer. For example a 2K primer renders the paint layer impermeable to moisture preventing micro blistering at a later date. Cromax refinishers can opt to use 635R, an etching primer, or wash primer surfacer aerosols 42R, 44R or 46R used as etching primers. Both provide excellent long-term protection against corrosion and blistering of bare metal.

Cromax  has also developed two direct-to-metal 2K low emission non sanding primer-surfacers - NS2602 and NS2607 – which are easy to apply and fast to recoat. They are suitable not only for direct to metal application on substrates such as steel, zinc and aluminium, but also over unsanded E-coats. With the addition of AZ9600 plastic additive they are also equally effective on exterior plastic vehicle components.

Cromax offers comprehensive practical and online training courses that cover body preparation and application techniques. To find out more, visit www.cromastore.co.uk.