Salt in Dust

[Stanley Covington]

I have read that dust contains salt, the sworn enemy of shiny steel. This makes sense for coastal areas, in the Salt Lake Valley, around dry lake beds, or where there are other sources of exposed salt, but is it true for dust in inhabited areas in general?

[george wilson]

I haven't ever had trouble with my machines just rusting. For quite a few years they were in storage after 1970 while I was musical instrument maker. They were in a basement,probably unheated for about 10 years,then,I loaned them to a person,then another. I had no place to keep them until about 1983.

No doubt it just depends upon where you are. Being near the sea doesn't help,I'm sure,nor does it help being near the salt lake.

[Stanley Covington]

I haven't ever had trouble with my machines just rusting. For quite a few years they were in storage after 1970 while I was musical instrument maker. They were in a basement,probably unheated for about 10 years,then,I loaned them to a person,then another. I had no place to keep them until about 1983.

No doubt it just depends upon where you are. Being near the sea doesn't help,I'm sure,nor does it help being near the salt lake.

George:

Thanks for the input. I grew up in the desert where rust was never an issue, and was shocked after experiencing the rust damage resulting from the high humidity (especially during the monsoon season) of Japan. And then I recently spent 1-1/2 years in Guam dunked in salty air and constant 85% humidity between daily rain showers/squalls and learned what serious rust was all about. So I guess I have been sensitized lately, and the thing about dust containing salt bothers me, because I am sure the dust in Guam was loaded with salt.

Did you store your machines in Williamsburg? I have only been there once, but it would seem close enough to the ocean for salt to be a problem, and the few days in summer I spent there with the wife and kids at Colonial Williamsburg were quite humid. Did you cover your machines while they were in storage to protect them from dust?

You have been doing this for a long time. What is your advice for rust prevention?

Thanks,

Stan

[george wilson]

I just keep the tables waxed. I bought my table saw new in 1963,and my bandsaw in 1964,used.

[David Posey]

I have always understood it to be the moisture that the dust retained that caused rust. I am sure that having salt in the air can make the problem worse. I've really only had problems here in Tennessee (with pretty high humidity) when I wasn't careful to make sure the dust was off my tools before I put them away.

[Stanley Covington]

I have always understood it to be the moisture that the dust retained that caused rust. I am sure that having salt in the air can make the problem worse. I've really only had problems here in Tennessee (with pretty high humidity) when I wasn't careful to make sure the dust was off my tools before I put them away.

David:

Dust retaining and conveying moisture is a serious problem of course, but the Cl in salt would be much more corrosive than dust-borne moisture alone, ergo my question about whether or not dust in general contains salt as some scribblers have written.

[Tyler A Anderson]

You have to have three things for corrosion to occur - metal, electrolyte (water) and electro-chemical potential. living near the ocean is much worse because you have more of both water and potential energy . Salt lake may have salty dust, but there is almost no moisture in the air.

That's why wax works. It keeps the water and salt from reacting with the metal.

If you put dry salt on bare steel with all of the oxygen removed - say in an air tight container filled with nitrogen, you wont get rust.

In reality, you can almost never remove all of any one of the three things, that's why everything is rusty.

[Stanley Covington]

You have to have three things for corrosion to occur - metal, electrolyte (water) and electro-chemical potential. living near the ocean is much worse because you have more of both water and potential energy . Salt lake may have salty dust, but there is almost no moisture in the air.

If you put dry salt on bare steel with all of the oxygen removed - say in an air tight container filled with nitrogen, you wont get rust.

In reality, you can almost never remove all of any one of the three things, that's why everything is rusty.

Tyler:

Thanks for the comments.

I agree with everything you say, especially the last sentence, and your point that the ions in salt accelerate the oxidation of steel in the presence of water. But I want to point out the obvious fact that, while the salty dust in the low humidity of the Salt Lake Valley will not generate rust as aggressively as the same dust would in the high humidity of Guam, given a fixed chemical composition of steel, and fixed temperature, and a fixed amount of humidity, salty dust will still accelerate redox reactions more than dust containing no salt would.

So, back to my question: Aside from coastal vicinities and areas with exposed concentrations of surface salt (such as in the vicinity of the Great Salt Lake or the dry lake beds of California and Nevada), is it true that dust in general contains salt?

Perhaps the question is too broad, but the statement I am referring to ("dust contains salt") is equally broad.

[Jessica Pierce-LaRose]

I might hazard a guess that household dust, where at least some amount comes from us and our pets might contain salt. This time of year, where I'm at, things start drying out, and accumulated road salt gets kicked up into the air - sometimes in some places you can almost taste it . . .

[Karl Andersson]

Stanley,
My job includes analyzing indoor air for contaminants, although salt isn't usually a human concern; there are lots of broad concepts in your question-"Dust" can contain a lot of things, as Joshua touches on. Soil dust will always contain some degree of mineral salts, either Sodium Chloride or a number of others, derived from weathering of minerals, sea salt deposits, etc.. Shop dust contains byproducts of your work and materials -wood dusts, abrasives, metal filings and so forth. Interior dust will always have a degree of soil dust in it, depending on the nature of the soil, dryness, wind, filtration systems for outside air, and other factors.

So, if you bet a beer on the answer, "virtually" all dust contains salts. Not all dust contains enough salts to be noticeably corrosive, depending on the level of soil dust and the salt content.

Shop dust containing wood fibers acts as a damp sponge when it absorbs moisture from condensation or precipitation (mists/fogs) and holds water against the metal longer, allowing the metals to oxidize if they aren't protected by oil or another barrier. If high-salt soil dust or salty sea air are part of this shop dust, the problem is magnified by the corrosive nature of the salts.

In very salty moist areas, like Guam, I wonder if tools could be fitted with small sacrifical magnesium anodes to make them rust less (as they do with boat motors and hulls). nah, probably would need to immerse them to get electrical continuity. But if it worked...the Japanese bi-metal golf bracelet industry could be repurposed.
Karl

[Bob Lang]

I think that a lot of wood dust is itself corrosive, some species more than others, and that can be a contributor to rusty tools as sell as the moisture absorbing properties mentioned. Salt would likely be a component of typical "dust" but that would vary greatly depending on location and/or time of year. Blaming all rust or other corrosion on salt alone seems way to simple to me, I think the corrosive properties of wood dust are the bigger culprit, at least in my neighborhood.

Bob Lang

[Stanley Covington]

So it sounds like the consensus to this point is: It is likely all dust may contain some salt, but the amount may or may not be enough to accelerate rusting to a significant degree.

The issue of wood dust contributing to corrosion was never a question, so unless someone is aware of wood species that naturally contain significant amounts of salt, it is not relevant.

I had not thought of road salt. It would be a major source of salt in dust, especially for those that park their wet vehicles in the same garage that houses their workshop in snowy months in locations such as the Midwest.

Thanks,

Stan

[Jessica Pierce-LaRose]

Karl's point about wood fibers absorbing moisture is a good one though - I've come across a few planes at flea markets and yard sales that were put away packed with dust and shavings and then stored in less than ideal conditions - the sawdust sort becomes a solid clump, and when you scrape it off, that's where the majority of the pitting and rust resides. Moisture that might evaporate away before it does too much damage sticks around, I guess. I don't think any of us are storing our tools that poorly, though.

[ray hampton]

the cities are trying to use other means to melt the snow/ice, beet juice are one way to cut -back on your salt, but the beet juice contains Vinegar, which is better having salt or vinegar flush into the river water

[george wilson]

Yabbut,I don't want a purple windshield,Ray.