Topic: Gypsum

[superdupa]

Hi,I have a  bit of my lottie which has clay soil,and was wondering if plasterers gypsum which is quite cheap and easy to get hold off will have the same benefits as garden gypsum which is expensive and difficult to find locally.Thanks for any info

[Mr Smith]

I think you will find that plasterers gypsum is not the same stuff, you have many differant types of plaster that all do a certain job and have a differant constituency, I would of thought what you require would be easy to get hold of from any gardening outlet, :) 

[Ellen K]

Gypsum is a hydrated form of calcium sulphate.  Plaster of Paris is gypsum with most of the water out - so when you mix it with water, it reforms as a solid.  You also get a significant exotherm so be a bit careful about sprinkling it on your garden and waiting for it to rain.

There is some debate as to how well gypsum really breaks up clay soils.  If you already have a high level of calcium in the soil (from liming say), adding more won't make any difference.  Some people say it works but takes 3 years.  One of my neighbours limes like crazy with 25kg bags of builders lime and his plot is like concrete.

I suspect it is one of those things you can demonstrate in a test tube but out in the real world it is like a toddler slapping a whale, the answer seems to be "dilute the clay with massive amts of organic matter" - compost and manure.  But if you give it a go, let us know how it goes.  Many of us are on heavy clay here so we're interested.

[Mr Smith]

We do have a big Gypsum mine on our doorstep, :)

[cornykev]

I thought u was having a go at my pikey mates again.    :o    :P       ;)

[Mr Smith]

I thought u was having a go at my pikey mates again.    :o    :P       ;)

      We do its called British Gypsum at Barrow on Soar, now if I had used the 'P' word I would of been getting all kinds of crap, ;)

[darkbrowneggs]

I am on very heavy clay, and tried for years adding manure, with little or no effect.  Then read Lawrence Hills book and followed his recipe for 4:1 Gypsum and Dolomitic limestone.  Didn't know there were different types of Gypsum so bought a ton bag from some commercial firm (never did use it all) 

Over the years it has made a vast difference to my soil  Lawrence Hills says not to expect fast results, but it is something to do with a chemical reaction which encourages the fine particles in the clay to bind together.

Certainly works for me.

 I still add compost - my own compost and muck piles are too weedy, so I put some on then  I buy the commercial stuff from the council and put that over the top.

[Vinlander]

The really great thing about gypsum is that it doesn't react badly with manure or other rotting stuff.

Lime with manure releases horrible ammonia, making the mess much more smelly and more than 50% of the nitrogen leaves with it. Gypsum actually helps to stop smells escaping from manured ground (though I'm not sure it would cope with it raw).

Dry plaster powder is burnt gypsum - no longer actuallygypsum (which is a particular crystal hydrate of calcium sulphate).

When plaster is mixed with water it takes in water as it sets and creates the hydrated crystals that lock together into a solid.

I think it's likely that set or spent plaster contains enough 'good' gypsum to be useful but not necessarily as much as 'proper' un-burned gypsum.

Apparently the burning process can produce some other forms of calcium sulphate that won't turn back into gypsum.

You've reminded me I was intending to do an experiment to prove whether spent plaster breaks clay.

But there's no harm in trying - there's nothing much in spent plaster you wouldn't want in your soil (except for maybe polyfilla which contains some kind of plastic glue).

There's vermiculite in browning plaster but not enough for it to make much difference - even if it was the 'wrong' (acid) kind - and if it's not the wrong kind it's a good soil-lightener anyway....

Cheers.