Bondo

[Chisholmcody]

So I have a issue with bondo. It's my first time doing body work and every time I bondo a small dent or anything of that nature I end up doing the spot 3-4 times and it's starting make me go crazy! I sand the spot tell it's smooth and then prime it and with the primer (2-3 coats of high fill) on the spot you can see the bondo line.

Is there any tricks to make this go away that I need to know. Also what's the best way to use the bondo? I end up getting pin he dots in the spot and end up having to go over it with glazing putty.
Any help will be appreciated. 

[bake74]

     You are not feathering the bondo enough.  Are you using progressively finer sand paper on the bondo after you use the cheese grater and block ?

[Chisholmcody]

using 220 grit for all of the sanding


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[bake74]

     You will need to go finer than that for feathering out so you do not see the lines.  Stop by an auto body shop and hit up some of the guys and ask what they use.  Most of the time they are willing to chat for a couple of minutes.

[Chisholmcody]

Ok thanks for the info!

[jaredts]

I'm not the best, but here's my take:
*some pinholes are going to happen, mix properly (watch a video if you've never seen someone mix filler properly) and use good pressure to apply the filler and they should be rare
*you just need to sand well beyond your filler with every sanding stroke so the surrounding steel acts as a guide.  This should eventually feather out the edges so they are not visible after prime/paint.  Look at it and feel it with your hand.  If it's going to show up after priming you should be able to feel it--keep sanding.

The techniques vary for very large or very small damage, but in general I learned to use 80 for shaping, 180 for refining and removing scratches, and follow up with high build primer.  If you have pinholes only use a putty with a hardener to fill them before priming.  For very small areas you may choose to sand the filler to 400 and use only a sealer over it instead of high build.  For large areas you might use the cheese grater.  Some might use it more than I do.  If you're only using 220 you may be giving up and priming before it's smooth enough because you're working way too hard.

[Chisholmcody]

Ok that makes since with the 220 I was sitting there sanding for 30min while the guys on youtube took 5-10

And thanks for the info


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[Blazin]

If you can get to the back side tap the metal as flat as possible with a body hammer & dolly first. Grind all the old paint, and of filler etc. off with 24 grit disc first. keep it moving, & don't try to take it to bare metal the first pass, back & forth, always keeping it moving with light pressure, If you are heavy handed, or try to take it all at once you risk warping the metal. Grind beyond the repair area at least as far as the width of the disc. I pre feather the paint to bare metal area with 80 grit on a 6" DA a little before spreading filler.

Mix your filler well as stated already. If its in a large flat area a larger spreader work well. Most times it takes more than one application to get it flat. I mix a little fiberglass resin in with my final coat to get it a little more creamy.

Start out with a block, and 36 grit, step up to 80 grit, always sanding at a 45 degree angel to the length of the panel. at a 90 degree angel to the other direction of the sand strokes. Alternate back & forth, 45 on way, 45 the other way. Its okay if the block ends got out onto the old paint. Always run your hand over the repair fingers to wrist, wrist to finger tips. You won't feel highs & lows with you hand 90 degrees to the length of the repair from side to side.

Finish feathering the 36, & or 80 grit scratches out of the paint from block sanding with 80 grit, then 180 on a DA.

Now it should be ready for priming with a high build urethane primer. You can block sand the prime with 180 if there is still imperfections, & reprime too.

[Chisholmcody]

Maybe that's my issue on feeling the spot I have been using my hole hand instead of my finger tips... And thanks for the info


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[Blazin]

You do use your whole hand. Starting on the unrepaired area you lay your hand as flat as you can. Run your hand over it length wise, all the way onto the unrepaired are on the other side. Finger tips to wrist, & back again wrist to finger tips.

[Chisholmcody]

Just re read what I posted....... Guess I should proof read first lol meant to say I've been using my finger tips instead of my hand ....my bad


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