A. Dave Crosby, an excavation contractor in Santa Fe, N.M., responds: Expansive demolition agents are a good alternative to explosives for quietly and safely breaking boulders into smaller pieces. They're shipped as a powder that you mix with water on site, and they have an expansive strength many times greater than that of rock or structural concrete. Several brands are available; I've used Dexpan (Archer Co., 866/272-4378, www.archerusa.com) with consistently good results. The procedure recommended by manufacturers is simple: With a rotary hammer, you drill holes of roughly 1 1/2 inches in diameter in a pattern and depth suitable for the material and desired result; then you place the mixed agent into the holes according to the manufacturer's instructions and leave the site. The next day, when you return, the rock should be broken.
In practice, I've found that drilling a 1 1/2-inch-diameter hole 24 inches deep into hard rock or heavily reinforced concrete is a lot easier said than done. When access or budget prevents the use of bigger tools, I drill 11/4-inch-diameter holes on 12-inch centers about 18 inches deep, then drill 3/4-inch-diameter holes to the same depth — or...
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