Removing rust, when is enough, enough?

Here is what I did with my IHC # 12 mower, built 1934-35. I took the main frame down to a commerical sandblaster. Spent $30, they wanted lunch money. I did not ask for a reciept. I then primed what was sand blasted with PPG's DPLF epoxy primer. I striped down the PTO, pitman and other small parts with a wire wheel mounted to a grinder. I then brushed Napa's rustconverter on with a disposable foam brush. Then sprayed with more DPLF and topcoated with ppg's concept in 70019 (IH50) and 10067 (IHblue, pre 47). A couple quick comments, The primer and paint I used is over kill, PPG's omni would be an excellent choice, I went with DPLF and Concept to get some practice in with it before I paint my allis G. The blue I used is more of a baby blue, I don't know much about the later blue but what I've seen its a much darker color.

Have you successfully used that exact combination so you are sure it works w/o a problem? I only mention it because Rustoleum specifically recommends against it. Here's the wording from the link:

"Can I use Rusty Metal Primer and Clean Metal Primer on my car?" "Stops Rust Auto Primer is formulated for use with automotive touch up paints. Rusty Metal and Clean Metal Primers should only be used if top coated with Rust-Oleum paint."

Rod

• Zero Rust

If you consider the Extend that I mention in my post below to VanO, the tech sheet for the Permatex product is here. The sheet for the Loctite product is here. I believe they are the same product since Permatex is under the Loctite corporate umbrella. The Permatex version is available at NAPA in small quantities - 8 oz I think for about $10. Despite what the tech sheets say, I would not recommend spraying the stuff. It sets up pretty fast. I almost ruined an expensive gun once that way. Since it sets up rather fast, it also is difficult to brush on with a bristle brush without leaving noticeable brush strokes. I have found that carefully using the throw-away foam brushes work well for applying it. The tech sheets also say you don't need another primer, but I use epoxy anyway, since I like it so much :o). I'd scuff the Extend with a Scotch-Brite pad before either priming or topcoating directly.

When I painted my AC-B gas tank I used Extend on the entire bottom area. some of the bottom portion of the tank was pretty tender with rust both inside and outside. It also had a couple of pinholes. I wound up brazing (caution - safety issue here!) the pinholes up but I didn't want to sandblast the tender area because I could have just made things worse. I lightly wire brushed the loose rust off. I then applied the Extend, epoxy-primed, then used a surfacer and finally topcoated. I would not have bothered with the surfacer on an implement. I also lined the tank interior with a heavy epoxy coating (not the same stuff as the primer). That was three years ago and there is no sign that the rust areas that were on the bottom of the tank have returned in any way.

There are other products than the Extend for such a treatment but I have no personal experience with them. I do believe the type of remaining rust that you speak of is not a situation where a phosphoric acid treatment would be called for. I consider that type of treatment as a minor surface rust removal, metal etch type of process. At least as far as the phosphoric acid treatments I have used in the past are concerned. There are many, many quick fixes claimed for rust out there. And a lot of hype, I suspect, to go with the claims. The best method is complete removal of all the rust, either by grinding or sandblasting. However, as in my tank case, that is not always practical and you have to choose a second best alternative. How one really makes an intelligent choice for that alternative amid all the claims is beyond me. I can only advise that the Extend has worked for me so far.

Rod