What Kind of Rock Makes a Good Wall?
By Mark Milligan and Carl Ege
The June 2001 Survey Notes article, “Where can I collect landscaping rock on public land?” generated more follow-up inquiries than any other “Glad You Asked” column. Many questions pertained to stone wall composition, which prompted us to research the subject.
Our investigations led us to conclude that stone walls in Utah are made of just about everything! Any stone that is not overly soft and crumbly seems to have been used for a wall.
The following photos are just a sampling of the variety of stone walls we saw in only one day and are located near the state capitol unless otherwise noted. Look around and you are sure to see many variations, including walls made with faux stone (concrete “rocks?”).
If you are considering building your own stone wall, libraries carry dozens of books that address the finer points of stone masonry. Bear in mind that unreinforced masonry is susceptible to damage during even moderate earthquakes. For high walls or those critical to holding back a slope, consult a geotechnical engineer.
Stone walls are of two basic types: dry stacked and mortared.
Mortared Historic Walls
Mortared stone walls have been built in Utah for more than 1,000 years.
Mortared Cobbles and Boulders
Any shape rock can be placed in any orientation when it is floated in mortar.
Mortared Nugget Sandstone
Both of these walls are built with Nugget Sandstone.
The stone on both of these walls is not structural, but a thin veneer.
The “Just About Everything” Wall
This wall is composed of black and mahogany obsidian, andesite, limestone, marble, crystalline calcite, travertine, jasper, agate, picturestone, wonderstone, sandstone, coal, petrified wood, algal boundstone, concrete block, broken concrete, broken tile, drill-hole core, 5-inch oncolite (algal ball), and a piece of petrified dinosaur bone.
Survey Notes, v. 36 no. 1, January 2004