Could Salt Blocks Act As Dehumidifiers?

[sandyRoe]

The house where I'm staying is damp, particularly under the stairs. Someone has suggested to the owner that salt blocks could help cure this problem.
It seems unlikely to me.
Any thoughts?

[TonyV]

salt will certainly absorb moister, although not a cure, just will alleviate issue.

[Buenchico]

Quote 1 (from a forum for caravanners):
"Last year, I used a cheap "value" kilo bag of table salt from Tesco/Asda/Aldi (or whoever has the best deal) in a pot dish. Cost about 30p.

Left it in the washing up bowl in the caravan sink. When I next checked it after about four weeks, the salt had turned to a solid block, but more importantly, the van interior was dry as a bone. Renewed with another 30p bag, and repeated monthly until we started using the van again".

Quote 2 (ibid):
"We use salt in washing up bowls and buckets placed around the cottage and caravan which are in France. It seems to work as there is quite a bit of water in them when we return. "

Source:
https://www.caravantalk.co.uk/community/topic/111328-cheap-d-i-y-moisture-absorber/

You'd get better results though by using calcium chloride, rather than sodium chloride, with something like this
https://www.wilko.com/en-uk/kilrock-damp-clear-moisture-trap/p/0135521
used with refills like these
https://www.wilko.com/en-uk/kilrock-500g-damp-clear-refill-sachets-2-pack/p/0410263

To save money, you could buy your calcium chloride in bulk
https://www.intralabs.co.uk/calcium-chloride/2kg-calcium-chloride.html

The same stuff must be available in Spain, although googling for 'cloruro de calcio' doesn't seem to find it easily.

[KARL]

In the UK the indoor humidity within a typical occasionally (timed/intermittent) heated home is routinely between 50% at very best in summer and frequently well above 70% in winter. Once the humidity goes above 60% the feel will become increasingly damp and as it approaches 70% some signs of dampness can become evident in places. If significant dampness problems are occurring then the humidity may frequently be above 80%, at least in places where air movement is minimal. As TonyV says, dry salt will certainly absorb water from a humid atmosphere but that is not where the idea stops. The volume of water that the salt would absorb, over say a week or even a month, will be less than the volume of the salt itself - just how much salt would you intend to put and keep in place ? If you were to compare with a dehumidifier, it would absorb litres in a month in quite a few, probably many, houses in the UK through much of the year.

[KARL]

For reference, if a kilo of salt absorbs its volume again of water then it will "capture" less than half a litre. Think in reverse: Put half a litre of water into a soup plate and wait for it to evaporate. This will take perhaps a week or more (two or three in extremes) and, in a room, you are not likely to notice a striking increase in humidity unless perhaps the room is quite small and completely sealed. I would wonder just how much difference it is going to make to remove half a litre of atmospheric moisture from an unoccupied space over a period of months.

[sandyRoe]

Salt doesn't look as though it's the answer to this problem.
There are dehumidifiers here so I'll use one of them. That means I'll need to run a power cable across the entrance hall.
I hope I don't trip over it when coming home from the cafe.
Thanks all for your help.

[sandyRoe]

Has calcium chloride any nefarious uses?
I'd have quite a job explaining to the police what I wanted it for if it has.

[theprof]

It has no nefarious uses sandyRoe. You can regard it as pretty innocuous. It even has an E number, E509 and is used in many food products in Europe. The anhydrous form is a dessicant that is very effective at absorbing up to about 150% of its own weight in water from the air. The hydrated form that Chris mentioned from Intralabs is not quite as good as the anhydrous form for your purpose but it will do the job.
Try not to accidentally ingest it though as it has an exothermic reaction with water and has been known to cause oral mucosa burns. It also seriously raises the calcium in the body rapidly, which has serious implications.

[theprof]

I chuckled when I read of the idea of using block salt.

In the UK, salt in the form of blocks is now only available for industrial purposes including water treatment, agricultural purposes and use in the chemical industry. The salt is an impure grade not suitable for human consumption.

I'm of the age to recall the days when you could buy block salt for human consumption in your local shops. I used to love crushing a piece of the block's large crystals under a rolling pin to produce something resembling table salt or crushing the piece by hand. These salt blocks would have been ideal for moisture absorption once the waxed paper was removed. They were cheap too.

Just try to buy culinary block salt nowadays!

[sandyRoe]

My post was too late to stop the purchase of the salt. There's 3 square blocks, each side about 8" long, here now.
I think they're intended as salt licks for animals.

[bhg481]

Block salt is available for use in water softeners and, as such, I assume is fit for human consumption.

[theprof]

bhg481, water softener salt is not suitable for human consumption. This grade falls within the category I mentioned in the second paragraph of my second post. It's classified as a grade known as "technical" in the chemical industry because it contains very small amounts of other chemical compounds and elements. It's impure and typically, technical grade sodium chloride can contain arsenic, cyanide and iron amongst other elements and compounds. This makes it unsuitable for human consumption. In fact, our former Lords and Masters in the EU make it a requirement that all water softener salt in any form is labelled as such on all packaging.

So, where does it come from? Well, most water softener salt is nothing more than halite, otherwise known as rock salt which has been processed to remove insoluble solids.

Why is it allowed to be used as a water softener? This is because relatively small quantities of the substance is used in water treatment domestically and it's rinsed away with clean water leaving little trace.

[theprof]

Animal salt links blocks are also made from a technical grade of salt but the crystal size is modified to suit and you can regard the salt as partially refined.
Table or cooking salt is known as PDV (Pure Dried Vacuum) salt as is at least 99.99% pure or higher.

[theprof]

Oops, links = lick.

[bhg481]

Thanks for that, prof