DryStoneGarden

I like to use brick walls to explain dry stone concepts, and I’ll probably never find a better demonstration photo than this one on website of the Dry Stone Walling Association of Canada. Brick wall concepts are straightforward: The vertical line between each brick is a joint. Each horizontal layer is called a course. Each course should break the joints of the course below it, a brick laid across the top of each individual joint. That way, if a joint starts to crack open, the opening can only run a single course before it bumps into something solid in the next one; it’ll have to staircase it’s way up instead of splitting along a straight line.

Stone walls built with rectangular stone work the same as a brick wall. A dry-stacked wall uses the heavier mass of the stone, greater thickness of the wall, and batter (a slight lean into the hillside or towards the center of the wall) to make up for the absence of mortar. Like with bricks, the stones should be laid flat, and the joints should be broken. Every stone should sit on two stones instead of just one, and in turn should have two stones sitting on it. It’s a good idea to occasionally break the horizontal joints with a double-high stone, but it’s not really necessary. The builder of the wall in the photo did a good job absorbing the irregularities of the stone into nice horizontal courses with sufficiently broken joints.

The wall also demonstrates two ways of capping a wall–with a large flat capstone, or with coping stones stacked vertical like books. Personally, I usually find vertical coping stones a bit self-conscious for my taste, but in this case the stepped coping works perfectly for this already self-conscious wall. (more…)

mongrel stone wall before

old moss rock wall after

Before and after photos of a dry stack wall we recently repaired. The original wall was built about fifty years ago with just a single rock type, and then at some point the red and grey river stones were added, probably during a repair job but also possibly because someone wanted to borrow stones for another one of the walls on the property.

The big issue obviously was the two cedar trees, which had pushed the wall apart and partially swallowed many of the original foundation stones. A few of the stones were literally engulfed by the root/trunk of the trees; we had to leave those embedded stones in place and just stack in front of them. We moved the wall forward six inches, added a gravel foundation and gravel backfill, and scavenged the yard for enough of the original moss rock to restack the wall with a single rock type, discarding the river stones. By the end of the day, we had just a single leftover rock about the size of a softball; every single other moss rock that we could find on the property had been used in the wall. Eventually the trees will push the wall apart again, but then it can be stacked one more time.

Last December we were hired to do a similar repair on another fifty-year-old wall that had been pushed over by a redwood tree. The difference with that wall, though, was that it had been built (poorly) with mortar. To repair that wall, we had to demolish it with hammers and we were unable to salvage almost any of the stone; it was fit only to be re-used as rubble backfill and we had to buy a pallet and a half of new stone. So the repair job became a replacement job. And, of course, it also became much more time-consuming and expensive, taking three times as long and costing four or five times as much money. It’s a big factor to consider in debates about mortar versus dry stack: mortared walls stand up well for a long time, but when they do eventually need repair work, it becomes a much bigger job to repair them and they frequently need to be completely replaced. Dry stack walls do typically need to be repaired more often, but those repairs are also typically much easier and much cheaper over the life of the wall.

ryan 12/7

cabernet stone

This was the first wall I built using Cabernet stone, a slatey type of stone from back east. I think the stone for this particular wall still has the best color of all the cabernet walls I’ve built.

cabernet wall detail

I usually avoid stacking across the point of another stone like I did in this section of the wall, but it’s fun to break the rules every once in a while. The point can act as a wedge and cause the stone to crack from the weight above it, but this wall is short and that stone doesn’t have a lot of weight above it so it should be okay.

cabernet stone

Another section of the wall, with Salvia clevelandii “Allen Chickering” going crazy on the right side of the photo. I had a fun pallet of stone to work with for this job; I found a couple of nice stretcher stones (a stone that stretches onto three or more stones instead of the usual two, great for breaking a long joint or solidifying a section made of smaller stones) and an angled capstone to step the wall down naturally. Typically, where a wall steps down we also try to plant something low and bushy to soften that spot like we did with silver thyme here. Ever since this wall, I’ve been pretty much hooked on cabernet as my wall stone of choice.

ryan 11/29

The wall stone in the header is called black lichen, a stone from Oregon. We planted erigeron (S.B. daisy) and woolly thyme in a few of the joints. Erigeron isn’t one of my favorites, but the client liked it, it was already in the yard, and it has the toughness to thrive in a wall. She said in Switzerland it’s called “thousand beauties.” I ‘m skeptical of Santa Barbara daisy, but I guess I am willing to plant “thousand beauties.” More details from that wall below.

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