Where can I buy a pound or two of this and not have the shipping be
crazy? Where could I buy it in say a local store? I have all the other
chemicals for my hydroponics except this one and I don't want to have
to buy a ton.

MJ

mj wrote:
Where can I buy a pound or two of this and not have the shipping be
crazy? Where could I buy it in say a local store? I have all the other
chemicals for my hydroponics except this one and I don't want to have
to buy a ton.

MJ


Plaster of Paris. You'll probably have to hydrate it to make it useful.

Bob

On Nov 8, 1:55*pm, zxcvbob wrote:
mj wrote:
Where can I buy a pound or two of this and not have the shipping be
crazy? Where could I buy it in say a local store? I have all the other
chemicals for my hydroponics except this one and I don't want to have
to buy a ton.

MJ

Plaster of Paris. *You'll probably have to hydrate it to make it useful..

Bob

As in every elementary school project plaster of Paris? I need it in
a dry form mixed with all the other stuff and then it is dissolved
into the water system.

mj wrote:
On Nov 8, 1:55 pm, zxcvbob wrote:
mj wrote:
Where can I buy a pound or two of this and not have the shipping be
crazy? Where could I buy it in say a local store? I have all the other
chemicals for my hydroponics except this one and I don't want to have
to buy a ton.
MJ
Plaster of Paris. You'll probably have to hydrate it to make it useful.

Bob

As in every elementary school project plaster of Paris? I need it in
a dry form mixed with all the other stuff and then it is dissolved
into the water system.


Yes. But you want hydrated calcium sulfate, CaSO4·2(H20), and Plaster
of Paris has been dehydrated to 2(CaSO4)·H2O. So you'll probably want
to add excess water, let it harden, then pulverize it.

Bob

On Nov 8, 2:13*pm, zxcvbob wrote:
mj wrote:
On Nov 8, 1:55 pm, zxcvbob wrote:
mj wrote:
Where can I buy a pound or two of this and not have the shipping be
crazy? Where could I buy it in say a local store? I have all the other
chemicals for my hydroponics except this one and I don't want to have
to buy a ton.
MJ
Plaster of Paris. *You'll probably have to hydrate it to make it useful.

Bob

As in every elementary school *project plaster of Paris? *I need it in
a dry form mixed with all the other stuff and then it is dissolved
into the water system.

Yes. *But you want hydrated calcium sulfate, CaSO4·2(H20), and Plaster
of Paris has been dehydrated to 2(CaSO4)·H2O. *So you'll probably want
to add excess water, let it harden, then pulverize it.

Bob

I failed chemistry, why harden it first, because just adding it to the
water in the system it will harden there? Thanks for all the help

mj wrote:
On Nov 8, 2:13 pm, zxcvbob wrote:
mj wrote:
On Nov 8, 1:55 pm, zxcvbob wrote:
mj wrote:
Where can I buy a pound or two of this and not have the shipping be
crazy? Where could I buy it in say a local store? I have all the other
chemicals for my hydroponics except this one and I don't want to have
to buy a ton.
MJ
Plaster of Paris. You'll probably have to hydrate it to make it useful.
Bob
As in every elementary school project plaster of Paris? I need it in
a dry form mixed with all the other stuff and then it is dissolved
into the water system.
Yes. But you want hydrated calcium sulfate, CaSO4·2(H20), and Plaster
of Paris has been dehydrated to 2(CaSO4)·H2O. So you'll probably want
to add excess water, let it harden, then pulverize it.

Bob

I failed chemistry, why harden it first, because just adding it to the
water in the system it will harden there? Thanks for all the help


I assume if you mix Plaster of Paris with the other stuff dry, the
other salts are hygroscopic and will absorb moisture from the air and
everything will clump up into little rocks. You haven't given enough
details about what you're planning to really know -- all I told you
was how to get the cheap gypsum. :-)

(You know Calcium Sulfate is not very soluble in water?)

Even cheaper would to tear the paper off a scrap of Sheetrock and use
use the white stuff inside, but it might not be pure enough for you.

Bob

mj wrote:
Where can I buy a pound or two of this and not have the shipping be
crazy? Where could I buy it in say a local store? I have all the other
chemicals for my hydroponics except this one and I don't want to have
to buy a ton.

MJ

Please consider that this is an international forum. How is anybody going
to answer your question as asked without knowing where you are?

You might also consider how pure the calcium sulphate needs to be. The
stuff sold for agricultural use often has small amounts of heavy metals in
it. I am not sure what the consequences of that would be in hydroponics.
You will pay much more per kilo for purified stuff than standard.

Thirdly consider why you are adding calcium sulphate. Is it to provide
mineral calcium or sulphur? There are some obvious substitutes for
providing calcium possibly some for sulphur if given some thought. There
may be side effects of substitution so if you don't follow the chemistry
involved you will have to stick to the formula you have been given.

David

On 11/8/10 10:30 AM, mj wrote:
Where can I buy a pound or two of this and not have the shipping be
crazy? Where could I buy it in say a local store? I have all the other
chemicals for my hydroponics except this one and I don't want to have
to buy a ton.

MJ

Many nurseries sell gypsum in small bags (5 or 10 pounds). But gypsum
is quite cheap. I think I paid less than $10 for a 50-pound sack at
Orchard Supply (OSH). But then, I use about 50 pounds a year to keep my
clay soil porous. I may use 100 pounds this winter, broadcasting it
over my entire front and back yards; it's been at least two years since
I did that.

--
David E. Ross
Climate: California Mediterranean
Sunset Zone: 21 -- interior Santa Monica Mountains with some ocean
influence (USDA 10a, very close to Sunset Zone 19)
Gardening diary at http://www.rossde.com/garden/diary