Preventing Tool Rust

When I turn on the heat in my uninsulated shop, you can almost watch the rust form on the machined surfaces of my tablesaw, jointer, etc. I tried commercial rust preventers, but they didn't last long or transferred to my project materials.

Purely by accident, I found that spar varnish, sprayed on my machine tabletops, effectively prevents rust. After a light sanding with 400-grit paper, the surfaces are shiny and smooth, with no transfer to my workpieces. It's been more than 6 months since the treatment, and I've not seen a speck of rust.
—John Gaeler, Keswick, Ont.