In most cases mechanical finishing is employed (1) to reveal the color of the mix ingredients, (2) to develop a texture or physical character for the finished surface, and (3) to eliminate surface variations. The most commonly used technique for surface removal is abrasive blasting. Abrasive blasting must be thought of as a total system including air source, sand pot, hose, nozzle, abrasive, operator, and operator protection. Another basic approach to producing texture is by mechanical fracturing. For this purpose a tool is used to impact the concrete, thereby mechanically removing part of the concrete surface. Scaling, brushhammering, jackhammering, and tooling fall under this category. The scaler is a pneumatic device with three piston-headed chisels that rotate and fracture the concrete surface on impact. While this method is usually more expensive than most abrasive blasting it is more forgiving in that it has a better ability to cover up surface defects than does blasting. Another commonly used method of mechanically fracturing the surface is by bushhammering. Usually these hammers are pneumatic, although electric or hand hammers can be used. This texture is also forgiving in that it has a tendency to cover up surface defects. Jackhammering is usually accomplished with one of two different types of tools: a chiseled or a pointed tool. In order to produce a good fractured particle surface, the tool must fracture the mortar the coarse aggregate alike. If jackhammering is to be performed at a time when the matrix is softer than the coarse aggregate, a chisel-type tool must be used. Tooling refers to the use of any sort of mechanical fracturing tool moved across a concrete surface in a prescribed pattern. Jigs can be set where as many as four or five pneumatic powered hammers are drawn together to produce a directional tooled type surface. Combination finishes involve the use of more than one basic finishing method as in the reeded and hammered finish. Other combination type finishes can be achieved by striating and abrasive blasting, reeding and bushhammering the leading edge, or reeding and then raking the surface with a hand or air-driven bull chisel.