Although it’s a typical part of a refinish repair, it’s a sad fact that the polishing process is something that collision centres generally don’t get paid for. This makes it a priority to ensure it’s as efficient and effective as possible, according to John Hristias, PPG Business Support Manager Asia / Pacific. While he has lots of best-practice tips and techniques up his sleeve, if John had to pick just one to make a significant impact, it would be as simple as taking a moment to clean between buffing stages.
The need to clean
We have all seen it happen before – a nice, shiny, refinish job goes back to its owner but then returns for a rework a short time later because the de-nib or swirl marks that were supposed to have been polished out, have reappeared. The reason is because they were not correctly polished out in the first place and the typical cause is that the detailer could not see them. It’s a common mistake but it’s an easy one to fix, no matter what polish system is being used. All it takes is adding the simple step of cleaning the surface with a 50:50 water methylated spirits solution after each polishing stage. For example, before moving from a lambs wool pad to a foam pad and so on. A super convenient options to do this is PPG’s SWX250 Water-Methylated Spirits Cleaner which comes accurately pre-mixed and ready to go.
The reason for cleaning the surface with water-metho is to remove any built up of polish compound so the operator can clearly see if the fine scratches have been removed. During the polishing process, compound can be forced into the scratches where it dries. Unless it’s removed, it can appear as if the scratches have been removed when, in fact, they have not. The only step where you don’t need to clean is when you are confident that all the scratches are removed and the final protective layer, such as MIRKA Polarshine 5 or Liquid Nano Wax, is being applied.
Don’t overload
Often, the need to clean between steps stems from one of the biggest polishing mistakes I see – overloading the polishing pad with compound. People might think ‘more is better’ but it actually works against what they are trying to achieve because pads are designed to work best with minimal compound. Rather than helping to polish out the scratches, the excessive compound just builds up across the face of the pad, stops the cutting action and clogs the surface. Instead, apply just a small amount of compound to the pad and use it to polish until there is none left before adding any more. Try to get used to the feel of the particular polish compound you are using – I call it the ‘glide’ of the product. How freely the pad glides, will give you a good indication of when it requires more compound.
Over time, buff pads can get caked with compound. To avoid this, get into the habit of washing all of the buff pads in warm water at the end of each week, then leave them to dry over the weekend so they are clean and ready go for the next working week.
Ghosting, swirls and holograms
To help effectively tackle them, it’s important to understand the ghosting, swirls and holograms you are trying to remove with the polishing process. For example, ‘ghosting’ typically occurs at a de-nib spot. It’s called ghosting because the outline around the outside of a de-nib spot gets highlighted. For this reason, it’s important to have as little impact as possible on the surface when removing a dust nib. To keep the job area small and reduce polishing time, de-nibbing with something like a MIRKA Polarstar SR 32mm disc makes it easy to focus on the tiny spot to be removed. Swirls or holograms are superfine scratch patterns typically caused by the combination of pads and equipment being used. In both cases, they create an appearance that is different to the panel surface around them which is why they standout.
Work to a best-practice process
Full step-by-step polishing instructions are available via a handy PPG Paint Rectification Process chart. Ask your PPG Territory Manager for a copy – it’s a perfect reference guide to have on your workshop wall.
Tips and techniques
- Invest in a good quality, variable speed polisher
- Look at each job and consider the best approach – polishing is not one-size-fits-all
- Use minimal compound and don’t overload pads
- Clean in between each polishing stage with a 50:50 water methylated spirits solution so you can see whether swirls have been removed
- Set the polisher to a slow speed. Higher speeds flick the compound off and make a mess – it can also overheat and impact the substrate below
Wash pads regularly to maintain their cutting performance