How to Mix Polyester Resin Filler

Updated February 21, 2017

Polyester resin filler, or Bondo, is a material that is used to fill dents or imperfections on the surface of metal. As polyester resin filler dries, it becomes a hard durable finish, nearly indistinguishable from what it has been moulded to. Commonly, this material is used in automobile body repair to even out surfaces before new paint is applied.

When working with polyester resin filler, pay close attention to blending the edges. When applied improperly, these products can be very hard to mask and require excessive sanding during the prep work.

Open the can of polyester resin filler. Use a flathead screw driver around the edges to help loosen the lid from the can.

Mix the putty to form a smooth consistency. Products like this tend to settle with solids on the bottom and the liquids on the top. Make sure the product is completely mixed before moving to the next step.

Take out the amount of putty you intend to use for the project. Polyester resin filler is a two-stage product, consisting of a putty and a catalyst. The catalyst is proportioned so that one tube will harden the full can of putty. Working with that ratio, a quarter can of putty requires one quarter of the catalyst to cure properly. Use separate tools to portion out the putty and the catalyst.

Mix the products together on a clean smooth surface. Consider using a tool that can be thrown away when you are finished. Paint stir sticks are an ideal tool for mixing polyester resin filler. Throw the mixing tool away as soon as you are done with it, and discard the proportioning tools as well. You do not want these products coming in contact with the one another by accident.


Polyester resin filler will dry more quickly in warm working conditions. Polyester resin filler will dry faster depending upon the amount of hardener used. Use a heat source to warm your project before apply polyester resign filler to prevent condensation problems.


You should not mix more hardener to speed drying time, as slower drying times are recommended. Too much hardener will cause the polyester resin to crystallise and become brittle.

Things You'll Need

  • Flathead screwdriver
  • Stir sticks
  • Smooth mixing surface
  • Blow dryer (optional)
Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author

Dakota Wright is a freelance journalist who enjoys sharing her knowledge with online readers. She has written for a variety of niche sites across the Internet including “Info Barrel and Down Home Basics.” Her recent work can be seen in “Backwoods Home Magazine.”