Rust!

One can only guess the cause if you are maintaining the humidity well. Send the photos to manufacturer. Could have been a weird batch with plating issues. Paint and plywood can have vapors emanating over time, which may be reacting with the plating.

You can stop it for good by wiping the rails with Ospho or a similar product. Used by anyone working with metal. Stops rust. Period.

I have seen similar results from any type of cleaning supplies stored in the vicinity. Cleaning products can be very caustic even when tightly capped.Particularly any acid containing products.

Why not paint/weather the rails so that they don't rust?

If it is not any water or cleaning products affecting your tracks that you know of, have you considered going to stainless steel track? Gargraves makes stainless steel track and I think that Ross Custom switches may have stainless steel track in some of their switches they sell. Where I live I use stainless steel track because of the humidity factor. Also have you checked under your track for plywood or what ever material that you are using underneath the track for leakage of moisture?

Dehumidifiers are only good for a small percentage of the moisture in the air, don't count on them for total protection.

Lee Fritz

I believe it's stainless outer rails, center rail is still blackened.  Stainless most likely will require mechanical wire connection, does  not solder well.   Black center rail, once the coating has been compromised will rust.  IMO.  Mike CT.

Wear surface top of track, the galvanize plating will be gone first.  Our (Fort Pitt Hi-railers) painted, Gargraves track/Ross switches,  has rust issues, which requires abrasive cleaning, which removes more galvanize, causing more rust problems. 

Your/my Atlas nickel silver track is quite different from tubular galvanized track.  

Then why not use some light oil on the top of the rail, i.e. Wahl Clipper oil, or Atlas Electro-Lube?

To prevent rust you need to keep the relative humidity below 40%. When the temperature goes down, the RH goes up, so the dehumidifier may need to be used in conjunction with a heater.  

I agree with the dehumidifier. I think all basements with trains should use one. 

romiller

have any pets that have accidents on the floor above?

Galvanizing, from somewhere above:

GG/Ross track is not "galvanized", it is plated with tin, an expensive, non-rusting metal that protects steel from rusting for a while. The old "tin cans" we not made of tin (who could afford that?), but were steel cans plated with tin. The thicker the plating, the longer it lasts.

Hence the word "tinplate". Tin, the metal, got to be thought of as cheap from the way it "rusted", but it didn't - the steel underneath rusted. Tin is costly.

===

My GG/Ross layout is in a 12X24 shop in the backyard; my track is painted as that looks better, to me. It rusts a little, but so what? The building is neither heated nor A/C'd unless in use. The layout is 25 years old, in a humid climate. It is still fully functional.

Embrace the Rust; become One with the Rust; real RR's rust like mad.

It's curious that the problem is in just that area around a switch. Is it possible there is some electrolytic action or stray currents accelerating the corrosion? Maybe some of our chemists or other experts can chime in.

All the issues are in the yard tracks nothing on the main lines.  Weird to say the least. I've lowered the dehumidifier to 40% from 50% hopefully that helps prevent anything from happening 

The main lines probably get a lot more train traffic than the yard.  Maybe that is why the rust only appears in the yard.

Earl

  Could just be that... track/plating. Even the electrical. (Maybe a sacrificial anode?)

But does any natural light hit it directly at a certain time of day??

    Especially in the A.M when metal is at its coolest, a warm light beam heats the water molecules in the air quickly, and those that contact the cool metal condensate there.

  Two minutes later the track heats from the light and the condensation evaporates.

    Or if a window is dead ahead of the camera some, the shadows cast on the track may be keeping it cooler right there. Same effect.

 The effect isn't really new news. Covering machines (correctly) doesn't just keep dust off, but light too.

Semi related- Toolboxes that change in temp and humidity slowly work best (wood boxes).