Q: “I’d like to build a fieldstone wall. What’s the best way to do it?”
—Norma Laren, Blackstone, Mass.
Roger Cook replies: Freestanding stone walls are a handsome way to define and improve your property. Building them is backbreaking work, but if done correctly, the wall will last a lifetime, if not a lot longer.
I like to set stones in mortar because you can’t beat a mortared wall for strength, which is important if a wall serves as seating or holds back earth. To preserve a dry-laid look, I set the stones in a mortar that’s pigmented a dark gray and then rake the joints clean.
Freestanding mortared walls, like the fieldstone one I’m building here, need a stable, frost-proof footing to prevent shifting, and that requires a lot of digging in cold climates.
Ask a stone yard to help determine how much material you’ll need, and have it delivered as close to the site as possible. Once built, you’ll have a rock-solid retaining wall without all the heavy mortar lines.
How to Build a Rock Wall
1. Prepare The Footing
- Dig a trench that’s below the frost line and 2 feet wider than the wall. Line it with landscape fabric overlapped 12 inches at the seams, add a 6-inch layer of ¾-inch stone, and tamp it with a plate compactor.
- Add and tamp more layers until the footing is about 8 inches below grade. About a foot beyond each end of a straight wall section, drive two stakes, separated by a distance equal to the width of the wall.
2. Lay The Base Course
- Connect the stakes with a mason’s line set just above grade. Place the first stone at a corner with its face grazing the line.
- Position the next stone against the first, face to the line, and so on until the first course is laid. Repeat on the opposite side.
- Fill between the two rows with smaller stones, set flush with the tops of the face stones. Top this course with a bed of mortar.
3. Build Up The Wall
- Reposition the line higher up the stakes and start the second course from a corner. Dry-fit each stone first to see that the vertical joints are staggered and the outside faces just touch the line.
- Remove the stone, spread a trowelful of mortar on the wall, and tamp the stone into it with a mallet. The face stones’ visible edges should rest only on stone, not mortar, so scrape away any mortar that squeezes out.
4. Mark The Stones to Cut
- Eventually, you’ll have to cut a stone to make it fit. Use a wax pencil to mark the sections of the stone you want to remove. (For this wall, the goal is to keep the joints tight, less than 1 ½ inches wide.)
- To make cuts, you’ll need a 3-inch carbide chisel, a 3-pound hand sledge, and safety glasses.
5. Cut The Stone
- Place the marked stone on the ground, waste-side down. Set the chisel’s carbide tip on the wax-pencil line, and aim it slightly downward.
- Strike the chisel once, then reposition it so that the blade is half on the score you just made and half on fresh stone. Strike it again and repeat until the waste pops off.
6. Tool The Joints
- Trowel the joints between the capstones with a brick jointer, making them slightly concave to channel away water.
- On hot, dry, or windy days, mist the wall with water as you work so that the mortar cures slowly and completely. Finish by applying a wedge of concrete along the base course, front and back, to keep the wall from shifting.
- Use a brick trowel to make each wedge 6 inches high and 12 inches wide. Hide them with backfill.