I've done 40-50 old tractors Paul and never had a problem with that. The coating though is so thin though that it isn't like paint in the respect that it leaves a thick coat at all. Even the clear they somehow do doesn't leave anything other than a clearer part. Say if you have a bolt that is pitted real bad, the zinc w/clear coating doesn't fill even the tiniest of pits, just puts enough on it to make it bright and shiny. Also, everything I have ever had done, they ask you to sandblast first. You probably take more off with the sandblasting that you put on with the coating. When doing a restoration, really a great way to go, at least on a tractor. Used to look so good I would leave certain bolts unpainted to add a little detail.
