Many people make bucket lists this time of year. My listing bucket includes taking time to read more.
This week I have been reading a wonderful new booklet by Sean Adcock entitled 'Stonework'. He does a thorough job of analyzing and explaining some of the structural aspects of bad dry stone walling.
Whilst I agree with almost everything he says about proper walling methods and why walls fall down, I do question a concept of his, in the section on grading where he looks at the logic of placing larger stones below smaller ones in a wall. The sentence I am wondering about is ... "Generally a big stone on top of a layer of two smaller stones is vulnerable and unstable compared to a layer of two small stones sitting on top of a big or over sized stone."
Listing the bucket to one side, and then vigorously shaking its contents of small random size stones will eventually cause the larger stones to all come to the top. It is evident that the stones in the bucket have now found a more settled, more stable state.
Stone arrangement before being 'shaken'
After shaking - the stones are fitted better and are less able to be 'stirred' .
I suggest that the same thing may well apply to certain random coursed walls. Smaller stones in the wall will naturally continue to find ways to slip down between,( hence get lower than) the bigger ones below them.
Therefore large stones might often be better bedded in a wall on a selection of a smaller stones to begin with, rather than having the smaller stones (especially if they are much smaller) placed above them, complying with the natural selection of sizes per height exhibited in the previous 'bucket of stones' example.