Gypsum for clay soil

No reason whatsoever.

Even better, if you can find a source of lumpy out of date plaster for free (try asking around).

Assorted rottable garbage also improves soils, so if you dig it up to add gypsum, you could add rubbish under the surface too. Unused plaster will bind the soil, used lumps wont.

NT

I don't really know the answer to your question, but I would warn you not to use gypsum if you want lime-hating plants such as heathers, rhododendrons etc

R.

Run it through a cement mixer and a couple of rocks as a ball mill. So long as you crunch it down enough to go through a sieve, it's fine. Even just soaking it in an excess of water would be enough (this is plaster, not cement).

I wouldn't add "rottable garbage" to soil either, it's much better to rot this down separately. Otherwise you'll be short of nitrogen and lawns in particular would suffer badly.

Yes - where about in the country are you?

Hmm. I know it is, but I am scptical.

Our clay overlies enough chalk, and though it helps, it does make the soil excessively alkaline.

We have found copius additions of orgamic material - peats, topsoils and manures - and sand, to be a better bet.

Its back breaking work as well. Hire a rotovator or small digger to break it up and mix it in.

As previous poster says, none really, except it sets hard and can make a mess of drainage in a particular area. The same is probably true of pure gypsum.

I've got areas of lawn that I simply left cement and plaster tailings under and heaps of builders sand, They don't fare well.

The easy way of of making flower gardens in clay, is mulch. That will decompose into decent topsoil, and you can pull annual weeds out of it. Wood or coca shell. Or peaty compost.

Or if its for vegetables, cheat: We made raised beds and filled them with gravel sand and topsoil. After breaking up the underlying clay pan just a little.

See sig. Ironically, in a village whose major industry is plasterboard ;-)

Chris

I've got one of the gypsum mines and processing facilities round the corner from me too. Ironically the dump bang over the road is unable to accept plasterboard for recycling(!)

could that be addressed by the fabled "joined up thinking" we are all looking forward to?

(IOW can you recycle old pb into new pb?)

Jim K

I must admit - I don't know if British Gypsum do recycling at the Mountfield/Robertsbridge plant. Though if they can take crap out the ground and turn it into plaster (they do all that here) I would have thought they would have added a preprocessing feed for doing whatever you need to old PB and sticking the result of it in with the raw materials from the mine.

Other sources seem to be of the opinion that one of the benefits of using gypsum is that it is essentially neutral, and will not alter pH.

Chris

Interesting how gypsum comes out of nasty thick clay pits, yet we put it back in as a clay improver?

If that's true, its news to me..

pretty sure that vinegar dripped on plasterboard fizzes..

I just checked, and its main constituent, calcium sulphate dihydrate is mildly alkaline. giving a typical PH of about 7.4

If its the raw plaster of paris, its even more alkaline at a ph of 11+

This is a TBE and a FQM (Totally Baffling Effect and Frequently Quoted Misunderstanding). You are chemically correct, but biochemically incorrect.

It isn't helped by the fact that the terms "acid soil" and "alkaline soil" are so misleading - which is the TBE. The reasons that those plants dislike lime has nothing to do with the acidity, but the fact that they have difficulty absorbing iron, and calcium interferes with one common form of plant's lime absorption. Sorry, I don't know the details. Magnesium doesn't have the same effect, for arcane chemical reasons, that I don't understand, either.

Regards, Nick Maclaren.

Now it makes a little more sense..

So they say, but I've not seen this happen in practice. If you added wood shavings or plenty of paper I daresay it would.

NT

Building plaster has other stuff in it besides gypsum, anyone know what those additives are?

NT

"Chris J Dixon" wrote

Chris, if you can find a Farmers Shop (not a Farm Shop) they may well sell Agricultural Gypsum in 25kg bags, which is what I bought. Mine was old stock, a bit lumpy, and I paid £5. each.