I am presently removing the lathe and plaster walls from my house. Since my yard needs building up I am considering using the plaster (lime and sand) as fill. Is this a bad idea? The existing soil is sandy/rocky. I would plan to cover the plaster with say 6 inches of the existing soil and 4 to six inches of top soil. Thanks for any input.
I'm no expert but I don't think that much lime would be very good for the soil. From what I understand, plaster is very alkaline and might burn any roots that find their way down to it. With your soil being sandy, the plaster might move towards the surface quicker than it would in heavier clay soils, the sand particles will filter down around the pieces of plaster like it does with the rocks. Anne
Actually, rhododendrons grow on dolomitic lime in China because the (admittedly copious) rainfall leaches the lime away from their roots which are in the ~acidic humus and moss on top of the limestone. Theoretically, dumping topsoil on top of the rubbish and planting in it could work. The key point is probably if the alkalinity of the debris is too high, and also if the lime or other noxious components of the plaster (including gases, perhaps) would permeate the root zone or float up into it during wet periods (should drainage become impeded). Probably it wouldn't matter if you were throwing it into a pit and then putting several feet of soil over the top, but a layer as shallow as you have described I'm not sure about. There is also the matter of what effect the rubbish might have on ground water or other nearby features, if any, and if there are regulations concerning the proper disposal of such material.
I really think that you might be creating a "lime-sink", but, of course it would depend upon just how much lime was involved. You did state "your house" so that tells me you are talking about not just one room. That is quite a bit of lime to expect nature to neutralize over any realistic period of time. And you taking responsibility to acidify the soil at any reasonable rate is having you assume a large and necessary burden on top of everything else you might have going. I would vote for the least amount of hassle, and have your 'destruct' house waste hauled and be done with it.
I think it is a good way to dispose of the material. With the moisture in the soil, plaster will quickly break up into sand. I don't think there aren't inert gases to be concerned about. Also, remember there is much more gypsum in plaster than lime and that is very thin. You just put enough lime in to make it trowel well. I have troweled many a wall. If there is much lime, it is in the lime-coat smooth finish. I am assuming the house is vintage, since few house have been plastered since the 1950s. The more soil on top, the better. I think plant roots tend to stop when they hit a change in soil media. If you build a raised bed, for instance, a good layer of sand on the bottom slows down roots reaching down and tree roots reaching up.
