preventing rust on CI surfaces

[daddo]

Redman said:

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Cast iron rusts. You can slow it down with various things but cast iron rusts. Let it get a patina, it'll look better. Cast iron rusts, even when liberally coated with oil.

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There ya go.

Guy down the road (Who sells wood) has a cast iron table saw sitting outside under a patio type cover. It gets indirect rain and moisture, he just wipes it with a towel and goes about his cutting. The blackish top doesn't seem to rust. Of course he uses it every day. Our humidity stays up there- usually higher than the outdoor temperature most of the time right now.
The one in my shop has that dark "patina" and it doesn't rust unless there is standing water on it from a cold drink I carelessly set on it- I just sand it down, give it a thin coat of whatever oil I got and go. No pitting, just stained- gave up on trying to stop rust and keep the shiny surface.
I do oil it once a year or so now.

[JimReed@Tallahassee]

All the tips posted are good. Here is what I do to mitigate rust issues. My garage shop in North Florida is a rust magnet. User handplanes get waxed and do pretty well if they are used frequently. Really good handplanes are kept inside and brought out only when needed. My rust did not get under control until I put in a dehumidifier. It keeps down the moisture. Covers, tool boxes, etc keep rust from condensation at a minimum.

[WilliamHodge]

If the moisture is so bad in your shop that cast iron is rusting,the wood in the rack must be getting soaked. High humidity in a shop will make the wood wet.

a dehumidifier solves both problems.

[bennybmn]

Dehumidifiers are tough if your shop is also a garage that gets opened regularly...

[cputnam]

I use Corrosion X HD. Got turned on to it during my salt water fishing days. Kept my CI rust free for 5 years of inactivity in the garage.

Truly synthetic motor oil is said to be as good. I'll try that when my 15 year old can of Corrosion X runs out.

[Restorer]

most sense on this subject I've heard here. cast iron from use develops a niece patina that really seems to stop rust. yes you will not have a bright shiney top, but most working shops don't. I do wax my tops on occasion, more for ease of use then anything else. If you insist a old sheet covering the top works as well as anything.

[Dennis Puskar]

I wax mine several times a year with johnsons paste wax, never had a problem with rust

[thewizzard]

If you don't mind a "patina", some of the oldest rust inhibition techniques known to man use surface modification followed by soap or oil. The most common is probably to build an iron-phosphate layer using phosphoric acid then sealing the surface with oil.

If you study up on these old techniques you will also find zinc salts mixed with the phosphoric acid provide a zinc-phosphate layer which can be further layered with sodium stearate (soap) for additional protection and lubricity.

Most wood shop people are used to seeing polished bright metal surfaces so you don't hear much about surface modification 'round here. If you don't mind greyish-blackish-greenish surfaces there are many less traveled paths to explore Now that black tools, wrenches, sockets ... ect. are en vogue versus the old shiny chrome ones, a big Parkerized table saw may make you the envy of all.

[Howard Acheson]

Keep this in mind regarding paste wax on cast iron. Paste wax is not imperious to water vapor. It will be imperious to liquid water by water vapor will pass right through.

You can verify this by waxing a CI surface and then spraying water on it. The water will "bead" but under each bead will be a spot of rust as the water droplet evaporates.

Fine Woodworking did a test a number of years ago and waxed section was one of the worst sections containing the most rust.

[Redman]

Also keep in mind that although cast iron does many things quite well the thing it arguably does the best is rust. You can use many different strategies to inhibit the rust but in the end cast iron will laugh at you and continue merrily rusting.