I've got 2 diamond warnings on a 60 van that have been on for a month+, pretty much detailed the van today (good clean) and noticed diamond rust patches under the magnetic stickers

Is this to do with the magnets? or trapped water?

Taken them off till I can get sticky ones

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Under-label corrosion is a big problem in the petrochems industry and this sounds like a typical case. Trapped moisture/process temperature/atmospheric conditions provide an ideal platform for corrosion to occur.

It used to be very common to see flow direction labels and contents ID (located directly) on high-spec painted unlagged pipework but corrosion can occur which is out of sight under the label until the dreaded leak begins. Even stainless steel pipework can be affected by stress corrosion cracking (different mechanism but same outcome) if the label adhesive contains chloride.

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Thanks for the reply SW3

Something i've never thought about, but like you say it normally happens 'out of sight'

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Always had the same problem, little rust marks appearing, solved it by having proper sign writing.

We only carry oxy/propane when needed, I might try wiping a film of silicone grease on the other side before sticking and see if I get the same problem

If so i'll have to go the sticker route with maybe a red magnetic line through if no gas onboard!

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