Ireland's Publication for the refinishing & associated Industries

Common body preparation mistakes and best practice

When it comes to refinishing, the quality of a finished article not only depends on the products used or the experience of the refinisher, but also on good body preparation techniques. DuPont Refinish provides its bodyshops with more than just paint solutions, and this includes body preparation products accompanied by first-class advice to ensure the perfect finish.

To achieve best practice in body preparation, refinishers must follow the key steps and avoid the common pitfalls.

Know your substrate and keep it clean
As basic as it sounds it is absolutely vital for refinishers 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 only completely avoidable within 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 conjuction 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 DuPont Refinish 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 DuPont Refinish 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. Refinishers need to demonstrate perfect hygiene at this point otherwise this can affect the final finish. By regularly changing gloves, and having separate overalls for preparation and a pair 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 DuPont Refinish 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 perfectly clean surface is obtained before the application of subsequent undercoats. Use DuPont Refinish 3911WB Final Clean 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 is 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. Refinishers should use DuPont Refinish 635R as an etching primer to provide excellent long-term protection against corrosion and blistering of bare metal. Alternatively they could use wash primer surfacer 825R.