I'm building a free-standing dry stack wall using ashlar scrap from a quarry (pieces of uniform thickness with completely flat top and bottom faces, but irregular sides):
Within each course of the wall, I will use stones of the same thickness. The final structure will be approximately 4 feet tall (6-8 courses total).
The stone is available in many shapes and sizes from small fragments of < 40 lb, up to the largest blocks that we can move without specialized equipment, ~300 lb. We have already used these largest pieces for our foundation and first course, but is there any advantage to using large pieces in the upper courses as well?
- Larger stones are more difficult and take longer to move and place
- Larger stones are more difficult to fit tightly with other pieces (without further shaping)
- Although the courses are of approximately uniform height, there are some slight variations that can cause stones in the next course to wobble and rock. Larger stones create more leverage and thus can wobble more easily, requiring careful shimming. Smaller pieces can more easily be placed to avoid wobble.
- Frictional force is proportional to mass. Larger stones are more resistant to lateral shifting.
- Showing off that I can move such heavy stones
The frictional advantage gained by using larger stones makes sense in a retaining wall, where there is the lateral pressure of the retained soil, but is there any reason to use larger stones in a free-standing wall? Other than unplanned loads like a tornado or a bus, I don't expect significant lateral loads on this wall.