I was doing a home repair and I had some bondo left over so I tested it as a filler material. It fills very well, will not shrink and it should be easy to mix color with it. Plus it dries hard enough to sand in about 10 minutes.
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This intrigues me. It would be a much simpler process than colored epoxy fill. Iāve read previously about ākneadingā the Bondo to reduce air pockets. Itās got to be much less finicky than the epoxy. My question is about the tint. I use paint for my epoxy (I know, a sin in some minds but Iāve never had setup issues with it) and it colors true to the tint. Does this work anywhere close with Bondo?
Trying to color the bondo (by adding color and mixing it well before adding the hardener) is going to be my next experiment, but I expect it will hold color well since it is really designed to be colored. Based on the quick experiment I did today it is 10 times easier and quicker than trying to use epoxy. There are no bubbles to worry about and it sands much better.
There is one downside, you cannot stain the board after you fill it with bondo, since the bondo really takes the stain.
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That would make things interesting. Iām thinking about a mask over the wood, cut out and Bondo. Might be a bit tedious then getting the Bondo flat and the masking off but it could work. I would think the colored Bondo wouldnāt leach into the pocket edges thereby eliminating that sealing step. All a trade offā¦ Iām interested in seeing your results. Iād give it a go tomorrow but Iāve currently got aluminum screwed to my table to cut out new gantry plates.
The bondo is sure a lot less expensive than the epoxy. A can of the stuff should last nearly forever.
Bondo is polyester based so it can use any dyes or tints compatible with fiberglass or resin products. Most brands come with a tinted cream hardener to help with mixing. If you are thorough, you can use the same clear liquid hardener for fiber glassing and it wonāt pre-tint (red and green is common). Add your color and hardener drops at the same time and when it is evenly colored, it is safe to say your hardener is evenly mixed.
You can refrigerate unmixed bondo to extend the work time before it gels.
Years ago I had a new hire on a large scale sculpture project. I handed him a can of bondo and hardener and told him to go to it. He had never used it before and squeezed the whole tube of hardener into a gallon can. Before he got halfway through mixing it, it got so hot it started smoking and we had to use a shovel to pick up the can to take it outside 
Are there any Aussie folk who know if there is an equivalent product down here?
Septone Auto-motive Body Filler, seems to be the most common body filler in Australia.
Thanks. Iāll get some
I use Evercoat tint for anything like this. Comes in a small rainbow of colors. Also, with bondo, if you sand it down and it exposes a bubble, you can fill it with bondo! 
The only caveat would be trying to mix and match the second batch color.
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You should be able to add the color to a ball of Bondo and mix it, then pinch off a bit and set it aside. Then add hardener to the remainder. If you need to patch for bubbles just add a drop of hardener to the bit you saved and the color should be exact.
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Brilliant! I may use that trick for epoxy too!
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