Fill pitting?

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sbarner

On Training Wheels
What we're learning here is that there are actually a variety of ways to fill rust pits. A couple of things to keep in mind, though. First, it is very difficult to get all the rust out. I like to use a combination of abrasive blasting and chemical treatment, but rust works its way into steel in the form of microscopic tentacles and it is virtually impossible to get it all out without removing the pitted metal. That's not usually possible on bicycle frames and parts, so you want to be very careful to do the most thorough job you can before covering everything up with filler and paint. Shiny, clean-looking metal that was once rusty can show rust again if merely left damp overnight. Someday that rust will resurface--your goal is to kick that can as far down the road as possible. This is why the best auto restorers don't try to clean up pitted sheet metal, but cut out the affected area and fabricate and weld in replacement metal. Bicycle sheet metal is thinner than that used on autos, so welding in patches is much more difficult. Be sure to apply a phosphate treatment before painting.

On a frame, my preference would be to fill with brass, not weld. The heat of brazing also seems to help neutralize the rust you couldn't get out. Don't work with lead unless you are at least in your late 60s, or have lived a harder life than your parents demanded, though it can provide an acceptable excuse for acting stupid.

Finally, if you use Bondo or any non-metal filler, be sure to seal it well before painting or the volatiles will work their way into the paint and discolor it.
 

1motime

Cruisin' on my Bluebird
Most old steel has some degree of pitting and age wear to the metal surface. Getting a good clean surface for a long lasting finish takes a lot of work, a good eye and attention to cleanliness. Strip all paint. Stripper, bead blast, wire wheeling, or a combo of all. If it heavily pitted and fairly thick do a light grind with 80 just to knock down the tips of the metal around the pit. Wire wheel thoroughly to get to the bottom of the pit. If still showing black rust keep doing it until the bottom looks clean. Using a acid metal prep might help at this point but make sure it ALL gets wiped off. If it dries do the process again. Most metal preps can only be removed by themselves. You want the metal to have about the same color all over. Not always possible with old. At this point don't touch with bare hands. Wipe with acetone and wipe again. Prime immediately with epoxy primer Catalyzed is best. Now you can fill with polyester putty or a thin filler.
Sand 80 until surrounding metal is hit. keep doing until everything is flush. Clean and epoxy. Don't let bare metal sit around unless that is your look. It will start rusting immediately .You can fill any lows still showing or spray with high fill primer.

Take it from there with normal paint prep. Lots of work depending on what your expectations are, how much time and money you want to invest. Takes lots of practice to get a nice finish easily. IMHO brass is only good for pieces that will be plated unless there is no other choice. Paint does not like brass.

Good luck!
 
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