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Moisture absorbing calcium chloride crystals



 
 
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  #1  
Old December 6th 06, 11:27 AM posted to uk.d-i-y
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Posts: 412
Default Moisture absorbing calcium chloride crystals

I have a little plastic thing from Woolworths into which I pour calcium
chloride crystals, to act as a moisture absorber in an under-stairs
cupboard which is damper than it ought to be.

What I'm left with after some time is a liquid and a solid mass.

If I pour off the liquid, and leave the solid mass in a warm dry place,
say on top of a radiator, will it be any good at absorbing moisture from
the air once again?

Are there like to be any nasty substances released into the air as it
dries?

Why am I left with a solid and a liquid, not just some dissolved calcium
chloride?

Thanks,

Daniele
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  #2  
Old December 6th 06, 11:38 AM posted to uk.d-i-y
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Posts: 173
Default Moisture absorbing calcium chloride crystals


"D.M. Procida" wrote in
message
...
I have a little plastic thing from Woolworths into which I pour calcium
chloride crystals, to act as a moisture absorber in an under-stairs
cupboard which is damper than it ought to be.

What I'm left with after some time is a liquid and a solid mass.

If I pour off the liquid, and leave the solid mass in a warm dry place,
say on top of a radiator, will it be any good at absorbing moisture from
the air once again?

Are there like to be any nasty substances released into the air as it
dries?

Why am I left with a solid and a liquid, not just some dissolved calcium
chloride?


If you leave it long enough you will get just liquid, the situation that you
describe is because the liquid is saturated.

I wouldn't bother trying to dry the stuff, you'll have an awful job
hammering the resultant solid block of the stuff back up, and it's pretty
cheap!

Julian.


  #3  
Old December 6th 06, 12:12 PM posted to uk.d-i-y
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Posts: 412
Default Moisture absorbing calcium chloride crystals

Julian wrote:

Why am I left with a solid and a liquid, not just some dissolved calcium
chloride?


If you leave it long enough you will get just liquid, the situation that you
describe is because the liquid is saturated.


So, the crystals started absorbing moisuture, to the point of being
dissolved in the moisture they were absorbing.

As this happens, the stuff heats up (apparently this reaction produces a
lot of heat) and the water becomes super-saturated, and continues to
dissolve more of the crystals.

Then it starts cooling down, and as it cools down some of the calcium
chloride precipitates out of the water.

Is that correct?

Daniele
  #4  
Old December 6th 06, 12:25 PM posted to uk.d-i-y
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Posts: 519
Default Moisture absorbing calcium chloride crystals

D.M. Procida wrote:
I have a little plastic thing from Woolworths into which I pour calcium
chloride crystals, to act as a moisture absorber in an under-stairs
cupboard which is damper than it ought to be.

What I'm left with after some time is a liquid and a solid mass.

If I pour off the liquid, and leave the solid mass in a warm dry place,
say on top of a radiator, will it be any good at absorbing moisture from
the air once again?

Are there like to be any nasty substances released into the air as it
dries?

Why am I left with a solid and a liquid, not just some dissolved calcium
chloride?


I suspect it's not pure CaCl.

Anyway.
Mere radiator won't cut it.
Take it all out, and place in a flat baking tray or something, and place
covered in an oven at 150C till dry.
Then break up and put the
  #5  
Old December 6th 06, 12:54 PM posted to uk.d-i-y
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Posts: 8,415
Default Moisture absorbing calcium chloride crystals

D.M. Procida wrote:

I have a little plastic thing from Woolworths into which I pour calcium
chloride crystals, to act as a moisture absorber in an under-stairs
cupboard which is damper than it ought to be.

What I'm left with after some time is a liquid and a solid mass.

If I pour off the liquid, and leave the solid mass in a warm dry place,
say on top of a radiator, will it be any good at absorbing moisture from
the air once again?

Are there like to be any nasty substances released into the air as it
dries?

Why am I left with a solid and a liquid, not just some dissolved calcium
chloride?

Thanks,

Daniele


These things are truly crap. If you redry them in the house all the
water vapour absorbed is dumped back into the air again.

If you keep using it, buying bagged lime from B&Q may prove cheaper.
But just as poor a performer. Fwiw quicklime would be more effective,
though less safe.


NT

  #6  
Old December 6th 06, 12:56 PM posted to uk.d-i-y
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Posts: 173
Default Moisture absorbing calcium chloride crystals


"D.M. Procida" wrote in
message
...
Julian wrote:

Why am I left with a solid and a liquid, not just some dissolved
calcium
chloride?


If you leave it long enough you will get just liquid, the situation that
you
describe is because the liquid is saturated.


So, the crystals started absorbing moisuture, to the point of being
dissolved in the moisture they were absorbing.

As this happens, the stuff heats up (apparently this reaction produces a
lot of heat) and the water becomes super-saturated, and continues to
dissolve more of the crystals.

Then it starts cooling down, and as it cools down some of the calcium
chloride precipitates out of the water.

Is that correct?


Not really - far too complicated! The crystals absorb moisture until they
start to dissolve, the liquid thus produced is also hydroscopic and
continues to absorb water until the crystals have all dissolved. After that
the liquid still absorbs further moisture, but with reducing affectivity as
the concentration of calcium chloride reduces.

I was once given one of those 'throwaway' dehumidifier containers once. It
had a mark on the side about 1/2 way up, when the level reached the mark it
was time for a new one.

Julian.


  #7  
Old December 6th 06, 01:23 PM posted to uk.d-i-y
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Posts: 412
Default Moisture absorbing calcium chloride crystals

Julian wrote:

Not really - far too complicated! The crystals absorb moisture until they
start to dissolve, the liquid thus produced is also hydroscopic and
continues to absorb water until the crystals have all dissolved. After that
the liquid still absorbs further moisture, but with reducing affectivity as
the concentration of calcium chloride reduces.


So I could leave it longer to absorb moisture, until all the solid has
disappeared? Would I be better off pouring the liquid or not?

Daniele
  #8  
Old December 6th 06, 01:41 PM posted to uk.d-i-y
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Posts: 5,146
Default Moisture absorbing calcium chloride crystals


D.M. Procida wrote:

If I pour off the liquid, and leave the solid mass in a warm dry place,
say on top of a radiator, will it be any good at absorbing moisture from
the air once again?


No, the solid mass is a mixture of calcium sulphate and calcium
carbonate -- basically trash impurities, because the "calcium chloride"
sold for these things is far from pure.

If you were to heat the calcium chloride solution and evaporate it, you
could recover the calcium chloride and re-use that. OTOH you'd probably
have to pay the energy costs of doing so. If you had a big damp problem
and a source of waste heat, then it _might_ start to make sense.

  #9  
Old December 7th 06, 01:38 AM posted to uk.d-i-y
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Posts: 519
Default Moisture absorbing calcium chloride crystals

D.M. Procida wrote:
Julian wrote:

Not really - far too complicated! The crystals absorb moisture until they
start to dissolve, the liquid thus produced is also hydroscopic and
continues to absorb water until the crystals have all dissolved. After that
the liquid still absorbs further moisture, but with reducing affectivity as
the concentration of calcium chloride reduces.


So I could leave it longer to absorb moisture, until all the solid has
disappeared? Would I be better off pouring the liquid or not?


Leave it.
What may make more difference is to take some packing tape, and go over
the door edge insides, so that you have half on the door, half off the door.
Then fold over the exposed edge of tape, so you have a draughtproofing
seal.
This may give some hope of the dehumidifier thing working, though it'd
really need a vapour barrier to do any good at all.

Does it actually reduce dampness at all?
  #10  
Old December 7th 06, 12:27 PM posted to uk.d-i-y
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Posts: 8,415
Default Moisture absorbing calcium chloride crystals

Ian Stirling wrote:

Does it actually reduce dampness at all?


from what I've seen of thesse things, they do absorb water vapour, but
the amount of absorption is only a small proportion of the damp
present, so they have approximately no effect on the situation. Theyre
basically junk products.


NT

 




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