cheap passive dehumidifier: wool sock full of rock salt

[grenzbegriff]

We have a strawbale/cob pantry that is heavily insulated but not well ventilated, and unheated, and in the winter it gets moist in there.

We've had success reducing the moisture in there with a homemade moisture absorber:

Old wool sock filled with rock salt, hanging above a pan.  Salt soaks up moisture very quickly, and in the hanging sock it percolates down to the bottom and drips into the pan.  We currently get about a quart of water a month from two socks. 

I regularly swap the pan with one in the cabin near the wood stove, so it doubles as a humidifier for that space which is very dry, as the water evaporates out of the pan.  The water comes with some salt, so eventually I'll take the salt out of the pan and put it back in the socks.  I've put these in other spaces like a shipping container just to help keep it dry.

I imagine the salt would prevent mold or nasty smells coming from socks of other material too, but in my experience wool is much better at not getting smelly or rotting like other materials do.  The wool may also help by efficiently wicking moisture into the salt, I am not sure how much difference it makes that way.  Would be interesting to experiment with a cotton sock vs wool sock.

[eyesonthehorizon]

I like how passive & closed the loop is. Do you know what humidity level is required to cause water to condense on the rock salt? I didn’t know plain dining salt was hygroscopic so I would have expected the dew point.

[grenzbegriff]

I don't know for sure, the temperature in there varies from around 45 to 65 and the humidity shown on the little hygrometer I have, which I am not confident of its accuracy, is also around 40-70 most of the time.

[eyesonthehorizon]

I don't know for sure, the temperature in there varies from around 45 to 65 and the humidity shown on the little hygrometer I have, which I am not confident of its accuracy, is also around 40-70 most of the time.

That would make sense. You’re probably right not to trust the hygrometer - it’s likely consistent with itself, which is really most of what you need, but most of them aren’t very accurate. Thanks!!

[grenzbegriff]

I think I see what you're getting at, that it's not so much a dehumidifier but more of a condensation trap so moisture that would otherwise condense elsewhere and cause mold or rust can be captured in the pan of saltwater.

It's similar to those silicagel moisture absorber things but in my experience is cheaper and nontoxic and can later be reused for other purposes.

[eyesonthehorizon]

I think I see what you're getting at, that it's not so much a dehumidifier but more of a condensation trap so moisture that would otherwise condense elsewhere and cause mold or rust can be captured in the pan of saltwater.

It's similar to those silicagel moisture absorber things but in my experience is cheaper and nontoxic and can later be reused for other purposes.

Silica gel is incredibly porous, which is why it works as a desiccant - for the salt to do the same, it must have some hygroscopic properties of its own, because I didn’t think it was especially porous!

Silica is also non-toxic unless there’s some additive, but it’s not something one should eat. If you find yourself in possession of some (I save the packets that come with food & medication for an artist friend) you can dry it in a low oven to reuse it!

[grenzbegriff]

Silica gel is incredibly porous, which is why it works as a desiccant - for the salt to do the same, it must have some hygroscopic properties of its own, because I didn’t think it was especially porous!
It does. :)  See a variety of explanations: https://www.google.com/search?q=why+does+salt+attract+moisture

Silica is also non-toxic unless there’s some additive, but it’s not something one should eat. If you find yourself in possession of some (I save the packets that come with food & medication for an artist friend) you can dry it in a low oven to reuse it!

I suppose if it's pure it can be; the one time I bought some it had a weird chemical smell.  I'll guess it wasn't the primary ingredients, but other stuff that got stuck to it during the manufacturing and/or packaging process.

[cannotWAIT]

You should submit this to Mother Earth News. It's exactly the kind of thing they love.