Techniques for Dry-Laid Stone Walls

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A good wall will outlast us all, so make it a fitting monument to yourself. For maximum stability over the coming centuries of changing temperatures, snow and rain, burrowing wildlife, and clambering kids, try to set every rock flat and horizontal in the wall so that gravity pulls straight down on it.
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Diagram 1: Dry-laid stone walls.
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Diagram 2: Dry-laid stone walls.
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Diagram 3: Dry-laid stone walls.
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Diagram 4: Dry-laid stone walls.

MOTHER’s Country Skills column discusses using techniques for dry-laid stone walls on the homestead. (See the dry-laid stone wall diagrams in the image gallery.)

Mortar has its place, but a stone wall that’s laid up “dry” and unaided by artificial adhesive or fillers seems more in keeping with a hunk of granite or mica schist formed when the earth was young, or a slab of sandstone or shale from the age of dinosaurs. A dry-laid stone wall (whether a low garden fence, a five-foot retaining wall, or a full-fledged house or barn) is held together by nothing but nature’s own gravity–plus your skill in arranging the stones so that each one lies flat and stays wedged in all around so it won’t slide out and collapse the wall.

Before you start building using techniques for dry-laid stone walls, check local zoning and land-use regulations. Like Hadrian’s Wall in the U.K., the Great Wall of China, and the stone fence that wanders all through our (once-cultivated) New England woods, a properly built dry stone wall will outlast any modern building, and a good many modem civilizations as well. So you may need a building permit, zoning variance, or engineering plan for even a low rock wall. All populated jurisdictions demand permits and inspections for high retaining walls and buildings of any size or construction. A structure intended for human habitation, especially if more than one story, must be built to code–and unmortared rock walls may not qualify (see Tom Elpel’s fine article on slipforming in this issue, which is code-acceptable most places and should be everywhere).

Rock is heavy, and even a low garden wall takes a lot of it, so be sure you are fit. Learn to lift with your legs, not your fragile spine. Get a pair of tough jeans, high ankle-protecting steel-toed boots, horsehide gloves, and if you plan to use a toothfaced rock hammer and mason’s chisel to dress stone and square its sides or remove wobble nobs, get a pair of safety glasses–and wear them; some soft and all hard rock can split off razor-sharp splinters and send them flying.

Rock Informs the Wall

Without mortar, the kind of rock you have available will determine your wall’s design. The more brick-shaped (uniformly thick, flat-surfaced, square-edged) the stone, the easier it builds. Weight equals stability, and the best walls are raised from rocks as large as the builder can lift easily, except perhaps the flat capstones saved for the top. But you can build walls from great boulders if you have the equipment to move them–a clamshell-equipped tractor if time is short, ramps and levers if it isn’t.

Nearly flat-faced walls can be made of thin and uniform slabs of slate or mudshale too; it just takes more of them and more time to dress and place them carefully. Rounded fieldstone can be laid up into a nobbly wall if the stones are chipped flat where necessary to make them hold still, and streambed table rock can be split out and broken up into wall size.

They tell me that you can buy stone in wall-building quantity, and you may have to if you can’t find rock locally. First, though, search for a local supply you can get for little or nothing. The world is made of rock, and all you need is to find a spot where man or nature has revealed it. Locate a streambed, washout, old quarry (look for crossed rock picks on your topo map), road cut, or cellar hole.

Layout and Foundation

Use stakes and twine to lay out your wall in straight sections. Buy a long piece of thin wood–24 feet of 1 1/2 inch hard pine lattice–to make a batten. Bent around stakes sunk at turns, it will define fair curves. Sink stakes every 8 feet or so along the back of the wall. Loop twine tight along them and (using a line-level to keep it horizontal) raise the line as you lay each course of rock. This level line (“batter-board” in old-time lingo) will guarantee that the rock layers (called courses) are flat and level so the wall will remain standing for the next few hundred years. Level course lines will also give it a competent, professional appearance you can be proud of. (Keep your courses evenly thick and horizontal even as the wall wanders over hills. You can terminate courses in steps or try to shim top rocks to make a smoothly undulating upper surface.)

Any wall needs a good footing to prevent its being washed out by rain or heaved by frost. For garage-sized and larger buildings, the code will decide depth, breadth, and materials for you; in general you must dig to below frost line and set the wall on a base pad of poured concrete reinforced with rebar.

You needn’t dig down to below frost for a simple wall. But always dig out all soft, dark loamy topsoil so the wall will rest on solid subsoil. For a small building, go deeper–down to light-colored firmly compacted sub-subsoil that is so hard it won’t dig with a shovel but needs a pick.

The footing–the track or concrete pad the wall rests on–should be at least half again the average thickness of the wall in width and depth. For a 2-foot-thick house wall in snow country, that’s a concrete pad 3 feet wide and as much thick, with its base a good 4 feet below ground. Of course, all the wall from there to ground level is lost to view forever. That’s a lot of rock and a lot of work to bury. For a handbuilt stone house, I’d dig and lay a concrete footing and foundation wall to ground level, and lay rock up from there.

For a small structure without sleeping quarters–such as the 10 by 12 spring house I built many years ago, or for a low retaining wall or any stone fence–you should be able to set a simple stone footing. A trench dug to solid subsoil with a two-course rock footing half again the width of the wall’s base thickness is a start.

Above ground dimensions are a matter of judgment and a function of height needed and the sizes of stone available. Really small walls, a foot or so high, aren’t walls so much as property lines. But once they approach 3 feet in height, no free-standing, dry-laid stone wall should be much less than 2 feet wide across the top.

Any wall needs at least two opposing face-tiers of rock, and a third down the center is better. If the wall is to be higher than 3 feet, increase its width by 2 to 6 inches for each foot of height. (The flatter, more uniform the stone, the more stable it will lie, thus the less width-increase needed.) You can make the whole wall wider, or lay lower courses wider than upper so the wall assumes a slight pyramidal shape.

So for an 8-foot-high wall of average flat rock that’s to be 2 feet thick at the top, make the footing 3 feet wide plus an added 3 inches for each of the 5 feet of height over 3 feet–an additional 15 inches. Round it up to an even 4 1/2-feet. Start the wall itself on the 4 1/2-foot-wide footing in the foundation trench at a width of 3 feet and gradually narrow it to a 2-foot width at the top. (Your favorite rock-building textbook or the local building code may give more specific width-to-height ratios.)

Scrape the soil in the footing bottom as flat as you can. When building on a slope, cut a series of near-level steps in the soil so each step will have a flat foundation. Aim the step bottoms slightly back into the hill so the foundation rock can’t slip forward and out.

Cut any large roots that cross the trench and cut brush and fell small trees that are within 10 feet of the wall. You’ll need the work space and you’ll prevent small trees from growing roots under the wall and, in time, heaving it up and over.

Dump budding rock in a line along–but a good 10 feet from–the footing trench. Sort rock into categories that match your building style–an individual way with rock that will emerge in time. You’ll want to save big smooth flats for the cap, rocks with a square corner for ends and corners, those with one good flat for the outer face, and so on. Wall building is a five-dimensional problem (encompassing the three dimensions of space plus the fourth dimension of time–lots of time–and the fifth dimension: sweat–lots of that as well). As you learn to create a wall from a rock pile you’ll automatically come to memorize special shapes, and will know intuitively where to find the perfect stone for every odd opening that presents itself as the wall rises.

Laying Dry-Laid Stone

A good wall will outlast us all, so make it a fitting monument to yourself. For maximum stability over the coming centuries of changing temperatures, snow and rain, burrowing wildlife, and clambering kids, try to set every rock flat and horizontal in the wall so that gravity pulls straight down on it. All walls–even when made from rounded fieldstone–should be laid in a sequence of horizontal courses.

Put your really large, uneven stones on the bottom of the foundation trench, whacking off irregularities or digging out the bottom for ungainly bumps so the flattest rock surface faces up.

If your rock is evenly thick, you have no choice but to make courses equally thick. If it varies, save your back, locate the biggest rocks on the bottom courses, making courses thinner as the wall rises. This decrease in course thickness as height increases gives your wall the appearance of timeless stability not unlike decreasing width/height gives the Great Pyramids (also laid up without a trowelful of mortar).

Arrange footing rock in the trench so the outer edge of each stone is a little higher than the inner–making each course slope down and in toward the center. As you build, maintain this slight inward slant so rocks will lean in against one another from each side; that way gravity pulls rocks down and in toward the centerline, effectively making the wall hold itself together for you.

With the footing course down, begin setting stones “one over two, two over one” so that every joint in a course is covered top and bottom by solid rock in courses above and below. This will eliminate “travel” of stones within the wall. Make sides flat and plumb, and adjust stones so the top of each course is as level and even as you can get it.

Inside the course, maneuver stones around in the flat so their convoluted edges nest and mate close as you can make the puzzle fit–and the course is as near to solid rock as you can make it. Fill cracks and holes with small rubble. As you complete each course, raise your level line to guide you when setting the next.

Use a mason’s level (with a forgiving wood body) to make outfacing surfaces of rock as vertical and smoothly aligned side-to-side as possible. From time to time, run a length of twine or your curve-batten along the front of the wall and whack back any stones that violate the plane defined by the twine. With care, good-splitting rock, and assiduous use of chisel and sledge, a skilled mason can raise a wall that is as perfectly flat and plumb as brick. Well, almost.

(Oh yes, lift each rock above its place in the wall and drop it the last inch or two.Trying to lay a 60-pound limestone slab in place gently is sure to squash a finger.)

Tie Stones

Never set narrow stones in the face of the wall with their relatively long dimension facing you; they’ll work out. Set them with long dimension running across the wall–effectively tying the outer faces together front-to-back.

Tie front and back faces as often as possible, alternating tie locations between courses. Never let a stack of tie stones or the seam between rocks run from one course to another. A wall will tend to pull apart or fold at stacked tie stones. A seam that persists through two or more courses is called run and is begging for the wall to balloon out at the crease and collapse in just a few years.

Each stone must be firmly set atop the stones that support it. Correct wobbles by shimming–pushing thin wedges or slivers of rock under the stones. Chunk, or fill voids between stones, with small stone and rubble. When chinking cracks in the outer faces, set wedge-shaped shims with the larger ends pinned inside the wall so they can’t work out.

Stone Wall Ends and Corners

Ends and corners are unsupported by flights of wall running off to each side. The freestanding faces are especially liable to work loose, so must be carefully tied into the wall with long rocks. Reserve especially long stones and lay them into alternating sides of every other course in building wall ends. Similarly, use long rocks to tie wall turns and corners into alternating right-left flights of fence.

Before setting table rocks on wall tops, take time to create a surface that matches their lower surface so the capstones will not wobble when walked on. This, too, takes practice; you learn to see the stone bottoms in reverse–kind of like photo negatives–so that where the stone has a pit, you make a bump.

It takes a little practice to lay up a solid wall, but not a whole lot if you have an affinity for the rock. One day you’ll find yourself tearing a section of wall down again and again and yet again, and then, just as all the wobbles are shimmed, the cracks closed, and faces set plumb, you realize that it’s getting harder and harder to see. Nightfall has slipped up on you, and you realize that you’ve been so lost in the fascination of the work that you haven’t noticed the time pass. Welcome to a trade that defies time.

Building Retaining Walls

Nothing so nicely defines the edge of a lawn or so elegantly keeps a sheer driveway-side soil bank from washing out as a stone retaining wall. But don’t make the common mistake of setting a single face-tier of rock into the soil and expecting it to hold. It won’t. Water pressure will buckle it.

You need to cut out enough of the soil bank to get in and build a proper stone wall–at least a 1 1/2-foot width of substantial rock laid one over two, two over one, in horizontal courses atop a proper footing. As you lay wall, run 2-inch-diameter plastic drainpipe through the wall every 6 to 10 running feet, pipe sloping slightly downhill, exiting the front of the wall about 3 inches above ground level. Then backfill behind the wall with a good 6- to 12-inch-thick sheet of crushed rock from the footing up to within a few inches of the surface. Fill the rest of the void with soil, and put a layer of soil and sod on top.

If you contemplate a major excavation and a really serious retaining wall–one over 6 feet in height or expected to hold back a hillside (even if well inside your property lines)–get the advice of a qualified road builder or engineer before you start digging, even if local law doesn’t require it. This is especially urgent in areas like coastal California, where the loose soil can mud-slide if laid bare–even if denuded of natural vegetation by fire. You may find that a few tons of hand-laid rock and gravel backfill won’t keep your hill from sliding into the next county come a major rain storm, and that to satisfy safety and environmental constraints you’d need to build a retaining wall of huge interlocking concrete hedgehogs fit for Boulder Dam. Better to leave the hillside to tree roots and shrubs that form nature’s retaining walls.

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