Painting Bondo

[flyboy2610]

I have a set of '72 doors that I plan to replace some areas on to get rid of rust through. The passenger side is my 'learning curve.' The drivers door is the one I really want to get right!
I welded up a couple of mirror mounting holes, ground them down, the used a brass hammer to just slightly indent the area. Gave it a thin coat of Bondo and got a smooth surface. I primed the area with Rustoleum primer, and when dry top coated it. When that was dry I clear coated it. All of this is rattle cans as I have no compressor suitable to paint with, nor do I have the space and equipment to spray paint.
The problem is I can tell where the Bondo is at. It just has a duller appearance than the surrounding metal. Is the a sealer or primer especially made for Bondo I need to get? I would like the final paint coat to be the same between the two surfaces. How do I achieve this?

[jimmy828]

I have a friend that is in the auto body field and i get tips from him and he recommends this for shallow indention's. It sands very good and can be applied to bare or primed/painted surfaces. Should also blend in better than bondo.

[sargentrs]

I sprayed a heavy first coat and, after it dried, could see where I had bondoed. I sprayed a second coat and it was less obvious. Then I sprayed a 3rd coat of primer/surfacer and it disappeared. Last coat was a white epoxy sealer. Sanded between each coat, 150 grit, 220 grit, then 400 grit before the white sealer. No visible bondo, hard as nails and smooth as a baby's bottom. I was using a spray gun though.

[72BahamaBlue]

For a spray can product, I've had good results with the Rustoleum self-etching primer. Home Depot has it, seems to provide a good cover to fillers without the dulling.

[flyboy2610]

Thanks, all! I'll try that Rustoleum self etching primer.

[mrollings53]

That self etching primer wont fix your problem. Bondo is porous. It soaks up paint, so you need to apply more coats to get the same amount of coverage. Apply a coat of primer, let it dry, then sand it smooth. Apply another coat, let it dry, then sand it smooth. Repeat this until the bondoed areas look the same as the rest of the surface. You'll also want to feather the paint out with each coat. For example start with a 6" circle on the first coat, a 12" circle on the second coat, and so on. Each coat should blend in with the one below it. While sanding the surface between coats run your hand along the surface across each layer. You don't want to be able to feel any sort of transistion between each coat. Once each bondoed area has been completely covered apply a couple coats of primer across the entire surface; sanding between each coat. Follow this up with whatever top coat you are using.

[chad67]

The problem you are having is partially due to the fact that rattle can paint is very thin (spray a little inside the can lid to see just how thin.) Bondo is porous as previously mentioned and soaks up paint like a sponge, especially really thin paint. Automotive primer is actually quite a bit thicker than the finish paints to help combat this.