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PPG Tech Tips – Body filler – filling in the gaps

John Hristias – PPG Business Support Manager Asia/Pacific

Body filler is a really basic part of the repair process but, because it’s so common, it’s very easy for bad habits to develop. In fact, I regularly see these bad habits and the negative impact they have, both on job productivity and the long term success of the repair. Like every part of the repair process, body filler should be analysed to make sure it’s as efficient and effective as possible.


Body fillers are designed to be used as recommended – trying something different is asking for trouble. For example, I see technicians doing dumb things like mixing heavy and light filler together so it’s easier to apply. I’ve also seen two different brands of filler mixed together or the hardener from a light filler used in a heavy filler and vice versa. I get to see the nasty results of non-recommended methods, including filler that’s difficult to apply, doesn’t adhere to the job, doesn’t feather-edge nicely and blisters under infrared curing.

Tips and recommendations

A step-by-step filler method is about standardising the process to ensure quality is built in from start to finish.

  • Recommended hardener ratio – Don’t think that adding extra hardener will make a better mixture – it can cause curing problems and wastes hardener so you run out before the filler can is empty.
  • Accurate percentage – You can’t accurately gauge the amount of hardener being added simply by looking at it – weigh it out so you know it’s accurate.
  • Mixing technique – We learned from a body filler manufacturer that the method which many tradespeople use – folding the filler in on the hardener again and again – actually pushes air into the mixture and creates pin-holes. The recommend technique is to pick up the hardener on the back of the mixing tool before pressing it into the filler using a side-to-side fishtail movement.
  • Application – Don’t trowel on a thick layer – start with a thin layer pressed firmly over the repair area, then build up successive thin layers. This reduces the likelihood of craters and pin-holes.
  • Wax & grease remover – Don’t drown a filler repair in wax & grease remover – it’s quickly absorbed by the filler all the way to the metal which can lead to blistering once heat is applied.
  • Bottom of the can – Even when body filler cans are sealed between uses, the last quarter often dries out. This makes it thick and difficult to spread, it doesn’t adhere well to substrates and you start to see blistering under infrared. Better to get a new can or use a cartridge system, such as Startline Ultra Body Filler (see below).
  • New technologies – Body filler technology is constantly evolving so don’t be afraid to experiment with new products. In many cases, a better filler can actually reduce the size of the repair. A good example is the Startline Ultra Body Filler with the Cartridge Dispenser system – the product is sealed in the cartridge until it’s used, it’s easy to precisely measure out the exact amount of filler and hardener required, it adheres to most substrates including galvanised steel, aluminium and plastic, it has a fine texture so it minimises pin-holes and it doesn’t blister under infrared.
  • Clearcoat – PPG doesn’t recommend applying body filler over OEM clearcoats. Clearcoats tend to soften in the sun and harden in the cool and this constant movement tends to cause shrinkage and movement in the filler.