It doesn't matter what you use, if you don't prepare it properly it's going to show through when you paint it. Bondo is prepped in the same manner as any other material before you paint it. Once it's prepped and primed properly you won't be able to see it at all.</p>

If you used microballons and it wasn't sandable then you did something wrong. This is a technique that has been used for decades by thousands of modelers. It's a proven strong and lightweight material that works great. If you used it once and it didn't work instead of dismissing the practice why not learn how to do it properly so that you can benefit from it? </p>

If you want to use bondo go ahead and use bondo. But as we said in your other thread, it's a very heavy material to be using as a filler. Also, bondo is designed to be applied as a body filler and should be applied in as thin of layers as you can get. When it's put on too thickly it crack from vibration and fall out. And the indent in your wheel pants is too thick to be using bondo.</p>

If you don't want to use epoxy and micro balloons then a great product would be Model Matrix from Epo-grip. It's basically an epoxy with milled fiberglass in it. It is very strong and will sand glass smooth. I've used it for doing some cowl repair and I'll never use anything else again. When I was at their booth at Top Gun they had a cowl that was built completely from Model Matrix. It's good stuff.</p>

Ken</p>