Body Fillers Explained

Body Fillers Explained

What is Body Filler?

In general, body fillers consist of a polyester resin with a cream hardener that forms a putty-like substance that is used to return a vehicle's body to its smooth surface after minor damage.

Their consistency and usage are similar, as well as the process that the substrate undergoes.

Different types of Body Filler?

Body fillers all fall into three general categories: standard, mid-range, and premium, and are generally available in a two part material consisting of a polyester resin and a cream hardener. The filler grade you selct will depend of the scope of the project and the size of the damaged spots needing to be repaired. Standard grade is a great option for minimal hail damage and small rust spots, while premium grade should be used for actual tears or a large surface area.

Standard Body Fillers

  • Standard grade body fillers are a lightweight substance or putty that spreads easily and cures in about 20-25 minutes. While not appropriate for use on galvanised steel, standard grade fillers are perfect for repairing minor dents and scratched. They sand easily to blend in with the rest of the vehicle once primed and painted.  Standard grade also offers the least stain-resistance.

Medium Body Fillers

  • Medium grade body fillers adhere well to a wide variety of body surfaces since they are fiber-glass filled. Due to being slightly higher wuality than the standardgrade, medium grade body fillers hold better stain-resistance. they are perfect for repairing small holes, tears and cracks in metal and fiberflass.

Premium Body Fillers

  • Made from top-quality resin that has the highest stain-resistance of the three, premium grade body fillers are the easiest to sand down and offer the best adhesion of filler matierals to underlying surfaces. This type of body filler is best used when high quality work is required or there are large areas or dents needing to be repaired.

Body Filler Tips

  • Always combine the exact amounts of filler and creme hardener as instructed on the packaging to achieve the best results. Too much hardener to filler ration and the filler will be brittle and crack, and too little will delay drying and hardening almost indefinitely.
  • Use a non-cardboard mixing board when combining the filler and hardener. Because of its absorbent properties, cardboard can affect the chemistry of the filler. Ultrimax sell the Mixing boards which are designed for mixing filler. Completing any filler projects on a warm dry day, as opposed to a humid day, will help the filler cure faster.
  • Never use filler over an area that has pre-exisitng rust. When rusty spots are not removed first, there is higher potential for staining and discoloration, and the filler will not adhere completely. For best results, remove the rust and then procees.  Filler adheres best to non-smooth surfaces, so sanding the area that needs improvement
  • To roughen the surface is essential to achieving the best results possible.
  • Because of its chemical make-up, make sure you're in a well ventilated area when using filler. Wearing a dust mask is recommended.

Where to use Body Fillers?

Body fillers have gained a bad reputation because so many people don't know how to apply body filler correctly - laying the mix on oo thickly without sanding or covering too large an area.

Body Filler should NOT be used on:

  • Rust - putting filler over rust will only make things look worse
  • Full gas tanks - body filler is flammable, and only resistant to gas once it is cured
  • Anywhere that gets too hot - you'll simply end up with a clumpy, popcorn ceiling-like look.

Body Filler Tips

  • You can use a plastic spreader but metal spreaders last longer and create a more defined edge
  • Make sure you have the correct ratios when mixing hardeners into your putty
  • Don't use cardboard as a mixing palette, because it is absorbent and will mess with the chemistry of the mix.
  • Have a thinner on hand in case your putty is drying too fast.
  • Use heat lamps to help the surface dry if you are doing this repair in cold or wet weather

Plastic Spreaders Vs. Metal Spreaders.

Many technicians don't like metal spreaders, while others swear by them. It's a matter of personal preference. One trick to to buy a whole box of plastic spreaders and use a fresh one everytime. A new, fresh spreader will apply the filler more evenly.

Using the right Fillers for the Right Job


Need More Advice

Why not get some help from our business specialists at Ultrimax who can advise on Body Fillers.

If you can't find a fix for the issue your're experiencing or you need more advice, drop us a line and we'll get your paint shop on track.

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