How to Build a Dry-Stacked Retaining Wall
Learn how to build a retaining wall using a variety of native stones in different shapes and sizes.
By John Shaw-Rimmington
How to Build Dry-Stacked Stone Walls: Design and Build Walls, Bridges and Follies Without Mortar (Firefly, 2016), by John Shaw-Rimmington, guides readers through step-by-step instructions for a variety of dry-stacked stone walls. Learn how to find native stones to save on costs. Follow the instructions as well as the photographs while building the wall. Find this excerpt in Chapter 2, “Stone Walls.”
There is an abundance of surface limestone and granite rocks in the Buckhorn area of Ontario. On this property alone, there was so much stone to be found in the hedgerows, as well as from the excavation sites for the pool and house, that no extra stone had to be brought in. There were some areas on the property where attempts had been made in the past to build with this gnarly stone, so we have tried to emulate this style in the walls we have built.
The chunks of stone, which are predominately limestone, are impossible to shape. One hit with a hammer causes the stone to break in totally unpredictable ways. The chunks of granite are too hard and too time-consuming
to try to shape, except where the tips need to be knocked off to fit. Our client asked us not to use any pink granite in the wall. This was odd as the pink granite is found naturally here, along the gneiss, schist and dolomitic rock deposits. We obliged her as much as possible, though we did not completely banish the pink granite.
Normally, we stand flat copestones vertically along the wall to cap the walls (a style known as vertical coping), but since none of the older walls in the area featured this configuration, we decided to lay the larger flat stones horizontally. They do a good job of securing the smaller stones along the top of the wall.
Step 1: Arranging the Stone
1. Locate and gather many more stones than you think you will need to build your wall. If you are buying stones and having them delivered, figure on 1 ton of stone per 2 linear feet of standard freestanding wall, 4 feet high. That will give you enough choice as you build and leave you some left over. If you are gathering stone, collect what you think are bad stones as well as good stones so you don’t have to break the good ones to make rubble filler. Always have enough selection available at the site to be able to work for at least the whole day. Remember, you need to have enough material to be selective as you work, since it’s unlikely you’ll be able to use every stone.
2. At the site, move your material by wheelbarrow or hand truck and separate the stones by size. Place them flat on the ground and spread them out as much as possible so that you can see them. However, if the ground is likely to freeze, you may want to leave them in piles so that only the bottom stones are likely to freeze to the ground.
3. When unloading stones, never throw stones onto other stones. They might break, and you can never make stones bigger again. If you must throw stones (off a truck for example), use the flat, more breakable ones tipped upright. If you are dumping stones on a driveway from a truck, first put down plywood and sand to soften the impact and cause less breakage and less damage to the driveway. Separate and store candidates for through stones, the long stones used to tie the wall together. Lay aside enough large, flat stones to use near the top of your wall and for coping. Leave paths through the piles of stone so that you can easily walk away from your wall to find the right stones. Leave ample room to walk along the sides of the wall as you build. This is also a safety precaution — you don’t want to have to step over or on top of stones as you walk along your wall. A spacious work site gives you room to make good decisions about fitting.
Step 2: The Foundation
A stable wall starts with creating a firm footing for foundation stones. Begin by digging a 6-inch-deep trench where the wall will stand. If the soil has already been disturbed, excavate to a depth where there is solid undisturbed ground.
In the trench, spread a clear, sharp ¾-inch gravel to a depth of 3 to 4 inches. The gravel provides drainage and a level support for the wall and should not consist of screenings, dust or any moisture-retaining material. It is serves as forgiving bedding for uneven stones and helps evenly disperse the weight of the larger stones used in the base.
Since any trench cut into the ground creates a place for water to collect, drainage is always an issue. A clear gravel base is less likely to compact or to create a dam that prevents water from flowing from one side of the wall to the other. If you do build a wall directly on the ground, remember that the weight of the finished wall may compact a sod or loamy surface, so be prepared for the wall to shrink a bit in height.
While it’s also possible to build a wall in a trench without preparing a base, it is always better to place the foundation stones on gravel rather than directly on porous soil. Stones may shift when frost causes the soil to expand, but gravel offers air pockets in which ice can expand and then melt away.
No tamping is necessary, as the stones and whole wall do better nestled into the slightly yielding base material rather than teetering on top of an unyielding surface.
The base material does not necessarily have to be absolutely level. When you build a wall with random stones, as opposed to modular blocks, you can bring the wall to level by using a combination of varying thicknesses as you build.
Establish a stable base for your stone wall with clear 3/4-inch gravel.
Step 3: The Foundation Course
The first course of stones is known as the foundation course. These stones should be placed, or bedded, into the gravel so that their faces are flush with the outside of the wall. Ideally, their heights relative to one another should be as level as possible to make building along and on top of them easier. This will take some doing, as large foundation stones, if they are not uniformly quarried stones, are often different heights and very different shapes.
With awkwardly shaped granite fieldstone, you can decide what the outside “face” will look like on the wall surface by determining what the worst side of your large stone is and then burying that side face down in the base gravel. This way, the gravel accommodates the awkward divots and rounded shapes. Make sure the bulk length of the stone is oriented so that it goes lengthways into the width of wall.
A foundation stone should be well supported by the gravel under it. Large cavities under big stones (especially flatter ones) can cause the stone to break or collapse into the vacant spaces.
If it is supported only at three or four points on the ground or by only a few smaller stones below, a course of foundation stones can eventually slump into the ground with the weight of the wall pushing down on them. That is why putting down a bed of gravel is the sensible step. The gravel provides even bedding underneath each stone.
If you are placing a very wide base stone, make sure there is still room to put a base stone flush with the outside of the wall on the other side. If it is too big, you may not be able to use it. Alternately, if you have a number of these wide stones, your wall may need to be widened in order to use them back to back.
Another solution is to bed one or two boulders well into the ground past the width of the wall and build the wall up and over them, conforming to the narrower typical dimensions of a dry stone wall. This is often the solution when bedrock or rocks that are too large to move are in the projected line of the wall.
The foundation course should be laid level and below grade.
Step 4: String Lines and Batter Boards
The strings of the batter board provide the angle of batter and serve as a guide for aligning each stone face along the wall.
I typically use string lines when I am building a straight wall; to try to build something straight without them is a little risky. I occasionally untie them in order to move a number of stones to the other side of the wall or to access a tricky spot, but these lines have are really essential to building a straight wall.
But you can’t just put string lines up and ignore them. Stones need to be lined up according to the level and plane that the string lines trace. You have to keep checking them.
There are two ways of putting up lines, both of which are useful. The first is to put up one line on either side of the wall, at the level to which you are working. When one level is complete, raise the lines to the next level. This is a very reliable way of building walls with all the same course heights. It helps, too, if you are creating or repairing a wall with random courses. However, it does make it difficult if several people are working on the wall at the same time. Inevitably, someone inadvertently leans into or pulls back the string lines while someone else is trying to sight down them.
There’s another solution to this problem, especially if you are building with more random courses or working with irregularly shaped material. Patrick McAfee, a terrific walling instructor, heritage masonry author and stone-and-lime-mortar expert from Ireland taught me this method.
With the McAfee method, you set up two pairs of lines well above the height at which everyone is working. That way you can sight down onto the two lines and maintain the plane and batter, or inward slope, of the wall. Each stone that you place should have its face aligned along the same plane defined by these lines. All the while, people can lean over the wall or move stones without disturbing your sighting. Closing one eye and taking care to fit each stone properly will keep all the faces of the stones flush along three dimensions.
It is still important to step back from time to time to check that the stones are all running level and horizontally along each section of random coursing and that you are still covering every joint.
Whatever method you choose, secure the string lines to the batter boards (upright stakes separated by spacers/adjustable brackets) that are set up at either end of the section of wall to be built. The boards provide a guide to the size, shape and batter of the wall.
Dry stone walls are generally built with what is called a “batter,” or a receding slope, so that if there is any movement of the wall (from frost, for example), the wall is able to shift back into its upright position rather than fall away. Walls without batter can last a long time, but they generally start leaning over in one direction sooner than batter-tapered walls do. A battered wall looks sturdier too. The closer to a pyramid shape the wall is, the sturdier it is, but an overly slant-sided wall starts to look less pleasing. The proper batter for a wall depends on the material being used to build the wall. The flatter the stone material is, the less batter is needed. Having said that, a typical wall generally leans in anywhere from 1 to 2 inches per foot of height.
A simple batter frame can be made with pieces of 1×2 wood screwed together so that the frame can be disassembled and reconfigured later with other wall dimensions. The batter frame should be secured with braces, screwed to a skid or propped up to something solid. Metal stakes can be driven into the ground, and these work well too.
How to Build Dry-Stacked Stone Walls: Design and Build Walls, Bridges and Follies Without Mortar
By John Shaw-Rimmington
Published by Firefly Books Ltd. 2016
Copyright © 2016 Firefly Books Ltd
Text copyright © 2016 John Shaw-Rimmington