Are you looking for a cold-weather project that will add a sense of solidity and style to your garden while solving landscape problems at the same time? Consider building a stone wall to level a slope for a terrace or planting area. Many wall-building techniques are well within the abilities of a homeowner, and the exercise will keep you warm on chilly days.
Retaining walls using natural stone can be built with or without mortar, a mix of Portland cement and sand. Walls built without mortar are called dry-stack walls. For the homeowner, dry stack walls have several advantages. Mortared walls require concrete footings reinforced with steel, to prevent the wall from breaking up when soil settles over time. Dry-stack walls can move with changes in the soil without coming apart so need no rigid foundations.
A dry-stack wall can be built at a more leisurely pace without worry of mortar setting up, and it’s is the method I suggest for initial projects.
To choose stone for your wall, visit a stone yard. Most have demonstration areas showing a variety of stones and construction techniques. Find them in the directory under “Stone –natural.”
Seattle stone yards include Pavingstone Supply in Ballard and Lakeview Stone & Garden near University Village.
When making your selection, keep in mind that flat stone is easier to stack than rounded stone.
Think about the size of stones, too.
Smaller stones are easier to lift into place than larger ones.
Above all, choose colors and textures that appeal to you.
Consider the height of your wall. Walls more than 3-feet high may need a permit and an engineer’s plan; check with your local municipality for regulations. To lessen the height of a wall, consider leveling a slope with two shorter walls stepping up the hill, instead of a single taller one. Retaining walls 14-to-20 inches tall can serve double-duty as seating, useful when you are entertaining a crowd.
Estimate how much stone you will need by multiplying the length of the wall by the height to calculate how many square feet (also called face feet) are in your project. Check with the stone yard to find out how many face feet per ton the stone you are interested in will cover, since it varies with the type of stone.
Building a wall is like putting together a 3-D puzzle. First, mark out the face of the wall with stakes at each end with string running between them. Next, create a solid base for the wall.
For short walls a foot or so high, tamp the soil down where the stone will go. For a taller wall or if the soil is wet clay, excavate a trench 8 inches deep and fill it with 4 inches of packed crushed rock for a firmer foundation and to put the base of the wall below the finished soil line.
For the first course use the largest stones to anchor the wall. While laying succeeding courses, remember the phrase “one over two and two over one,” placing a stone so that it rests on two stones beneath. This staggers the joints in the wall and increases its strength.
You may need to use a hammer and a stone chisel to take off parts of a stone to make it fit better. Use smaller pieces of rock as wedges and shims to stabilize individual stones.
As you build, taper the wall back about 2 to 3 inches for each foot of wall height, so the wall leans into the hill. As each course goes up, fill in behind it with soil and tamp it down. In walls more than 2 feet high, backfill with gravel to provide drainage to keep water from backing up behind the wall, particularly in clay soil.
Step back occasionally from the wall to check the overall effect. Good walls have a lively flow to the pattern.
Save out the flattest, widest stones to make a cap for your wall, giving it a finished look, and if it is be used for seating, a comfortable top.
For good information about wall building, consider “Stonescaping: A Guide to Using Stone in Your Garden,” by Seattle author Jan Kowalczewski Whitner (Garden Way Publishing).
Phil Wood is the owner of Phil Wood Garden Design in Seattle and is a widely published freelance writer.