Q: I'd like to create walkways and a driveway for my 18th-century house using something called soil cement. Can you tell me more about it?
I'd like to create walkways and a driveway for my 18th-century house using something called soil cement, a material used extensively at Colonial Williamsburg. Can you tell me more about it?
— Donald Boisvert, Foster, Rhode Island
Kevin O'Connor replies: Soil cements these days are highly compacted, water-permeable, and very durable mixes of soil and aggregate with a small amount of portland cement—just 4 to 6 percent—as a binder. It's relatively inexpensive because the soil can be pretty much whatever is available at the site, except for clay or highly organic topsoil. This kind of material would probably work well on your driveway, according to the Portland Cement Association.
doesn't use portland cement on its pathways; the material wasn't available until the late 19th century. Mark Wenger, director of facilities, says that most public pathways are pea or cracked gravels mixed with sand and clay, spread in a 3-inch-thick layer, then compacted with a roller. They're so solid that they need touching up only once a year.
A few paths are covered with crushed oyster shells, which closely resemble marl, a mixture of clay and shells the colonists mined from local seabeds and spread on their pathways. Wenger's crew dresses the oyster-shell paths annually with a 1-inch layer of fresh shells. No compacting is needed; they quickly interlock to form a solid, quick-draining surface.
In areas with lots of wheelchair and stroller traffic, Wenger goes high tech and covers paths with a two-inch layer of pea gravel held together with polyurethane resin. He says the resin darkens the color of the aggregate somewhat, but the overall look is in keeping with the 18th-century surroundings. According to Bill Phillips, vice president of , the company that makes the resin, this aggregate is tough enough for a driveway as well.