Originally Posted by The Toecutter
But is paint alone really sufficient? I've heard horror stories of rust bubbles popping up where people have drilled holes, even after they had painted them over.
Rust of course is corrosion of a ferrous metal.
Corrosion requires Oxygen and Water.
To stop corrosion you have to stop either or preferebly both Oxygen and water form contacting the metal.
This can be done with paint., but just as not all paints are the same , not all users preperation of the material to be painted is the same --and this is the important part in prevernting rust.
When drilling a hole in steel it rarely is a clean cut , often leaving burrs.
These burrs on the edge of the hole often have sharp edge with very little surface area for the paint to stick too.
If the paint doesnt cover the metal well it will rust.
So deburr any new holes with either a file or an overside drill bit., and slightly radius the holes edges. (both sides)
The smoother you get the hole the greater chance paint will cover it evenly with no thin spots.
Paint choice is also important.
has an excellent range of rust inhibiting paints.
I havent used them myslef but they have an excelent rep with hot rodders and restorers world wide.
I have used normal single part epoxy rust proofing paints with great success.
Also another thing to look for ,,if your drilling into a previously painted surface you may lift surounding paint breaking its bond to the metal.
if this happens you must paint over it to seal out air or remove the paint chip and then paint it.
And of course , preperation is 99% of the job.
Prepare well , keep it grease free and paint with good stuff and you wont have rust problems.
PS , if the hole is just for a self tapper screw , use either a zinc plated or galvinized screw and dip the thread into paint before screwing it in.
This will take the paint into the threaded joint (thats what a self tapper does) and seal out air. (hopefully)
if you have access , paint the other side of the screw with paint.
You can also do the same thing with rivets.