Gypsum for clay soil

[The Natural Philosopher]

worms will take care of reducing grass clippings to compost!

But in general, yes. 3 years and then apply compost. You can hurry it along, but why bother?

Gardening is a long term investment.

[Bob Hobden]

"Tim Watts" wrote

British Gypsum make cat litter too, Nature Cat Gold, so that is probably also gypsum and it's in granules too. Should be available at any good pet place or could be ordered, but check the price first. Worth ringing BG first to find out if it is pure gypsum.

[The Natural Philosopher]

filler mainly. Mica and so on. that's yer carlite bonding anyway.

The finishing plaster is almost pure gypsum IIRC.

[stuart noble]

AIUI gypsum is the raw mineral, which doesn't set when mixed with water. It has to be hydrated to make plaster.

[The Natural Philosopher]

T'other way about. Gypsum is the hydrated stuff, which has to be reducedd (de hydrated) to make plaster..then addition of water rehydrates it, and it crystallises into solid chunks.

[NT]

Vegetable garbage does wonders for the worm population, which produce a fair bit of good poop. If there is such a thing.

NT

[Chris Hogg]

Many years ago, most gypsum was mined; a great deal of it came from Belgium and northern France; hence the name Plaster of Paris. However, the modern desulphurisation of flue gases from coal-fired power stations, using a slurry of hydrated lime and ending up with a slurry of (mostly) gypsum, has resulted in lots of cheap gypsum as a waste by-product. This means that gypsum mining is no longer commercially viable except for specialist application that can carry the cost. The conversion of hydrated lime to calcium sulphate (gypsum) during the desulphurisation process is not 100% efficient, simply because the efficiency of sulphur oxide absorption drops off when there's not much lime left in suspension, so it's not cost-effective to keep using the lime slurry until it's 100% converted. After filtering and drying, the residual lime in the gypsum reacts with carbon dioxide in the air to give calcium carbonate (think: lime mortar). Hence most of the gypsum currently available will fizz with dilute acid, and has an alkaline pH. Pure gypsum doesn't fizz in this way, and naturally has an acid pH.

The reason some plants dislike 'lime' has a great deal to do with soil acidity. In this context, 'lime' actually means calcium carbonate (chalk), rather than quicklime (calcium oxide) or hydrated lime (calcium hydroxide), both of which convert fairly quickly in the soil to calcium carbonate by reacting with carbon dioxide in the air. 'Limey' soils, i.e. chalky soils, typically have pH values of around 8 to 8.5. So-called lime-hating plants such as many of the ericaceae have a greater requirement for iron (and possibly manganese), than other plants. The solubility of iron and manganese in the soil decreases significantly as the soil pH increases from say pH 6 to pH

8.5 (neutral is pH 7), a typical range of soil values. At the high pH, there just isn't enough iron and manganese available in the soil to be taken up by the plants to satisfy their needs, and yellowing of the leaves (chlorosis) is the result. It has nothing to do with the presence of calcium in the soil per se. Pure gypsum (not the modern stuff from desulphurisation) used to be recommended as an additive to heavy soils to open them up, where it was wanted to grow rhododendrons, in place of 'lime' which has a similar effect on the soil but is alkaline.

[Chris Hogg]

Gypsum is the fully hydrated form (di-hydrate, CaSO4.2H2O). There are several types of plaster, but the common one is the hemi-hydrate (CaSO4.½H2O), made by heating gypsum to around 125°C, when it loses water. On suspending in water, this reverts to the di-hydrate and sets.

[The Natural Philosopher]

Interesting. We just compost ours.

takes a fair time to rot down, and the rats get a fair bit.

[The Natural Philosopher]

Thank you!

well written and increases understanding. Can't ask for more!

now to buy some of that manganese and iron feed for the 'ericaceous' tubs.

[Andy Dingley]

No quote chopping, so that it hits the archive fully.

So what's the stuff from the graden centres? Pure gypsum rather than FGDS, so as to avoid the alkalinity change?

[Ian B]

No, that's made from bentonite clay, which is the most absorbent, clumpy dirt the Earth can offer.

Ian

[stuart noble]

Ah, right! But gypsum, as in agricultural gypsum, presumably doesn't set then? Not that it makes much difference when it's mixed with soil.

I'd think about vermiculite as a conditioner. Okay, you have to break the clay up to incorporate it (which probably does more to improve it than any additives), but it aerates the soil permanently and doesn't break down into anything else. Just don't buy the agricultural grade, which is rather over-priced.

[Chris Hogg]

I've never bought any, so I can't comment, but my guess would be the latter. A simple pH test would tell you.

[The Natural Philosopher]

there would be no reason to supply anything other than the dihydrate for any purpose other than actually making plaster.

Its costlier and has shorter shelf life.

[Andrew Gabriel]

Building gypsum sets initially when you dump it outside, but as it's slightly soluable anyway (which is why damp eventually destroys plasterwork), it quickly crumbles apart again when kept wet, and plants have no problems pushing roots through it. Grass seems to love growing on it.

[Tim Watts]

Yes indeed. The bit of my lawn used last year for dumping plaster washings (from mixing) is fine. In fact the grit from the coal ash bucket seems to be upsetting it more.

[Weatherlawyer]

Gypsum is calcium sulphate which is more or less neutral but is calcium rich which will hurt alpines. Nothing seems to hurt rosydandelions.

Sand is neutral and acid. Use a mix of sand and gypsum with sawdust or shedded organic stuff. Grow lupins for a while. Any nitrogen loss will soon come back.

Sand and clay =3D loam. I think sand and gypsum =3D marl.

[AJH]

Does this mean I can re vitalise old multifinish by heating it to

125C?

I've just had to recycle 980kg of plaster materials (at a cost of 65 quid plus delivery) which I suspect is about 30% of what the builders purchased. I've gone right off dot and dabbed plasterboarding as a result even given the time saving. Conventional plaster also is easier to fix to.

AJH

[The Natural Philosopher]

I thought it was a bit hotter than that..

and it will bneed re grinding in a ball mill or similar, but yes, in principle..