- Question: What is bushhammering and how is it used in concrete construction?
Answer: Bushhammering is the use of impact tools to remove mortar and fracture aggregate at an exposed concrete surface. The amount of removal can vary significantly, depending on the application. Think of bushhammering as more aggressive than sandblasting and usually less severe than scabbling. Hand tools or bits for electric and pneumatic hammers are used, depending on the desired surface texture, the amount of surface to be tooled, and the location of the work. A special tool for bushhammering has several conical or pyramidal points, and resembles a meat tenderizer. Similar effects can be achieved by using pointed or chisel bits or needle scalers. Bushhammering is done for various purposes. It can produce pleasing surface textures varying from a light scaling to a deep reveal of coarse aggregates. Other applications include removing fins, protrusions, or drips that can form on concrete during construction, or mineral deposits that can build up on concrete over time. Because it increases roughness, bushhammering also can be used to prepare concrete surfaces before patching. Marble, calcite, and limestone aggregates are well-suited for concrete to be bushhammered for architectural purposes. Natural gravel can shatter or break out of the cement paste, while hard granite and quartz aggregates can break erratically or into the paste, rather than across the intended surface. Most structural concretes can be bushhammered. Use air-entrained low-slump mixes, properly placed and vibrated. Gap-graded and low-sand-content mixes are recommended for best appearance. Concrete can be bushhammered after it reaches a strength of about 4000 psi and is at least two to three weeks old and surface dry. Be careful when working close to an edge or corner. It's a good idea to do a sample area for acceptance by the owner and specifier before beginning work. This can minimize misunderstandings about the intent or quality of the work.