Rock is a great material to work with. It’s cheap – especially when you live rurally where you can pick it up off the ground – and easy to use. It’s also strong and natural, the earth’s building blocks. The downside is that it’s labor intensive and slow, compared to other building methods.
The principle of rockwork is simple. It’s exactly like laying bricks, other than your bricks are not uniform in size and shape. Basically, each level overlaps the one below it. The join between two rocks is a weak spot. You counter this by placing a rock on top of that join to bridge it.
No wall should lean, unless that wall is part of an arch or dome. If a rock wall leans, the weight will be shifted away from the center of the wall, and will eventually crack and fall down. So make sure each level of rocks is plumb and level with the one below it.
Beyond that, you pick your style of rock work. Some people like straight, uniform faces; others prefer a more rounded, less perfect effect. You can also cut your rocks, to get that perfect fit, but we have never tried that method and would not assume to guess at the technique.
You can create spectacular effects and works of art with rocks, provided you have the time.
Something we use a lot where we live now is dry stacking (mortar-less rockwork). We have red, misshapen rocks all over the place. They’re not particularly useful for building, but they are great for retaining walls in things like swales and terraces. And, of course, they’re free and right where we need them to be.
Seeing as our property is a hill, we do a lot of work on the pasture, to prevent run-off and encourage more plant-life. For this purpose, we stack rocks in rows along the contours, then backfill with dirt. We then stack the next layer of rocks partly on the back-filled dirt, instead of the previous rock layer, so that the wall leans into the hill.
We have seen dry-stacked rock walls stretch for miles and miles, as old property lines and fences. They have lasted for a long time, and are generally in great shape. For the most part, they are wider at the base than at the top, and they also use rocks that fit very well together.
We wouldn’t suggest dry stacking for tall walls. To do so, it seems like you would need to use larger, heavier rocks that are cut to fit exactly. An easier option would be to use mortar.
Mortar makes the jigsaw aspect of rock work a little easier. Rocks still need to fit pretty well together, but the mortar will absorb small imbalances. Many people use concrete as mortar, but adobe works too.
The idea of mortar is not to let rock touch rock. Every stone should be surrounded by mortar. You put your mortar on any exposed rock, excluding the “faces” of the rocks, and stack a rock on that mortar, much like brick laying.
You can use a paintbrush or sponge, and water, to smooth the mortar and to really bond the mortar to the rock.
Another way to do rock work that is a little quicker is to set up forms for your wall or foundation. You pour a layer of concrete into the form, then fit rocks in the form with the faces pushed up against the form. Pour more concrete in between each rock and on top of them and continue with the next layer. This sort of slip forming rock work is very fast, but it won’t give you as nice of a finish as a properly made stone wall.
Rock work is satisfying, but slow. You can use rocks for walls, foundations, flooring and for arches. It might take a little practice to become good at it, but worth the effort.