My father has regaled me since childhood with stories of his grandfather splitting rocks, big rocks, boulders, by heating them with fires and then quenching them with water. The thermal shock fractures the rock making it so that one can remove pieces easily. This is safer than dynamite and a bit more accessible.
A benefit that my father had failed to mention is that by doing this sort of fracturing one ends up with many cubic pieces that are great for building walls and cairns. The fractures run along crystal faults much of the time turning round rocks into pieces with nice flat faces.
Over the past five years I’ve been gradually cutting a new road through ledge, in part using this technique. It works amazingly well and has the side benefit of satisfying young pyromaniacs taste for fire. I asked Will, my older son, if I was creating a pyro or curing one with all those fires. His reply was “both!” Realize that for really big rocks and ledge we often burn the fire all day long and even over multiple days as we work the rock. After a while the thrill of the fire dims a bit and it becomes one more chore. I doubt Will will end up “like the mayor’s son.”
I remember Sam, he was the village idiot.
And though it seems a pity, it
He loved to burn down houses just to watch the glow,
And nothing could be done,
Because he was the mayor’s son.
–Tom Lehre, “My Home Town”
The burning rock bonfires serve other purposes too. It saves on doing dishes, makes for a fun outdoor meal, cleans up wood that is not suitable for household use, provides ash that can used to sweeten our very acidic soil and charcoal which the livestock like to chew on. Apparently eating charcoal helps with digestion, parasites and toxins. In some cultures they regularly eat charcoal to deal with environmental poisons. And, less I forget it and someone else point it out, burning wood produces CO2 which increases the greenhouse gases that cause global warming, something we appreciate here in Vermont. Since I don’t have a SUV or drive much I figure this will have to do for my personal contribution.
Of course, with any bonfire, be careful and don’t burn during dry seasons or let the fire get away from you. Keeping some five gallon pails of water on hand lets you soak down around the fire.
Lastly, if you do split rock with fire and water, beware of the steam which can burn you and that the rock can throw shrapnel. This is one of those – “do it at your own risk” type projects.
At this point I estimate that using this among other techniques I have removed approximately…
(50’x20’x6′ + 14×8’x2’x4′) = 6,896 cu-ft of granite ledge
6,896 cu-ft x 168 lbs/cu-ft = 1,158,528 lbs of granite ledge
Eek! That’s a lot! Over a five year period it comes to 231,705 lbs/year or 115 tons/year or 3.9 tons/week (warm weather work) so I guess that really isn’t so outlandish as it seems at first blush.