Body Filler

My initial choice for body filler is Bondo. Bondo used to have a bad wrap in the 70s, mainly because people wouldn't apply it properly and it would crack, split or fall off. It's changed a lot since then and is very durable. It is a two part filler that you add a little bit of red hardner to the grey filler to activate it. It is only workable for about 10 minutes so you only mix a little bit at a time. I start with about a softball size and as I progressed I used less and less. Once it starts to harden, it will not spread smoothly. Throw it away even though there's a compelling urge to use up the last drop. If you use it past this point, you're making more sanding work for yourself and will most likely have to do it over again anyways.

Quite a few professional bodymen have advised me that Evercoat makes a very good filler that is nicer to work with then Bondo and its about the same price. I've since tried the Evercoat and found that it wasn't much different except that it was a greenish blue when mixed. I didn't realize it but I do use Evercoat Everglaze & spot Putty for finishing work and its a great product, so I'll definitely try the rest of their product line.

I'm doing the bodywork during the winter months and my garage, even though its heated, is about 50 degF which is below the rated working temperature for the filler. I keep the filler in my house so that its at a higher temperature and only bring it into the garage when I need it. I also let it cure for a longer time before I sand it. I found that at lower temperatures, it doesn't spread very good, it is too stiff. At room temperatures, it spreads very nice.

When it is cold, it takes a long time for the Bondo to cure. I have had to wait up to a week this past month as we had -20 degF weather and I can't afford to keep the garage heated when its that cold. If you try to sand Bondo that isn't cured yet, the sandpaper gets clogged very fast - within minutes. I thought that I had bought poor quality sand paper but the solution is to wait a day or two then it sands without clogging.

Now that it is summer, here's what I've found on mixing filler (Bondo or Evercoat). It is better to apply more hardner than too little. You want it to cure within 30 minutes. This way you can work with it quickly. The ideal progress of the filler is as follows:

  • When first mixed, it should be easily spread for about 5 minutes like peanut butter
  • It should start hardening and can't be spread. You can start shaping with a cheese grater tool or with a sharp blade. It'll have the consistency of clay. You can scrape off any lumps or high points quite easily.
  • Next it'll harden but if you try to sand it, it'll gum up your sand paper - now you wait. If you didn't put enough hardner in, you will have to wait a long time which probably was the problem that I had in the winter time.
  • After about 20 to 30 minutes from first mixing, you should be able to sand it relatively easily. You may have to use 40 grit to start and then go to 80 grit.
  • If you wait until the next day, the filler will be super hard and very difficult to sand.

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Copyright Aug 2011 Eugene Blanchard