Friday, February 25, 2011
What aggregate to use in ecobuilding
I want to talk about the sand and other aggregates we use in hemp and lime plaster. This should apply to other mixes too. Firstly Sand: where does yours come from? A neighbour of mine told me that in the recent past people would collect sand from the river and wash it out in barrels. This seemed fairly low impact to me, so we gave it a go. The sand we collected had been dredged out of a harbour a mile or so from our house. So transport and environmental damage was low. If we had disturbed the delicate river bank this wouldn't have been such a good idea. The sand we collected was very fine. This led to some cracking of the plaster which had no hemp in it. But I would use it again. We have also used ground sandstone from the local quarry. (Commercial quarrying is not my favourite to be honest, which is something to bear in mind when deciding how much lime you want to use in your build. Making your own lime putty in the traditional way is preferable. And using as little as possible) A few weeks ago I attended a talk about eskers and their biodiversity. I didn't know an esker is a deposit of sand and gravel laid down by melt water rivers beneath glaciers. They look like low serpentine hills running across the landscape. Because of the relative high drainage compared to the surrounding fields they tend to have very interesting plant, insect and other species. They are also commonly excavated for building aggregates. This is usually small scale for local use (think less miles) however the mining can upset species populations. This is quite a problem, particularly in some areas. I won't go further into the politics! So what sand can be used? We know beach sand is a bad idea because of salt and also habitat destruction. A nice idea is to use recycled glass. Have a look if there is someone producing glass "sand" near you. Another thing to remember is that waste on your building site can often be ground up and used in a mix. We have been able to use our slate waste for a path. A couple of minutes in a cement mixer will knock off the sharp edges. Does anyone else have any ideas?
Posted by Phoebe at 11:15 AM