broach

A broach is a wide, flat-edged cutting tool used to shape and dress stone surfaces. Unlike a pointed chisel that works by concentrated impact, a broach presents a broad cutting edge, typically 2 to 4 inches wide, that removes material across a larger area with each strike. The tool has a handle at one end and a beveled cutting edge at the other, struck with a hammer or mallet to plane down rough stone or remove tool marks left by pointing chisels.

In stone masonry, the broach sits between rough-splitting tools and fine finishing tools. After a stone is split or roughly shaped, masons use the broach to flatten faces and create an even plane. The cutting edge is always kept at a shallow angle to the stone surface, allowing the tool to shave rather than gouge. This produces the characteristic textured finish visible on dressed stone, particularly on ashlar blocks and architectural elements where a deliberate pattern or surface quality is desired.

Broaches are made from tempered steel with edges that must hold under repeated impact. The width of the cutting edge varies with the job: narrow broaches around 1.5 inches suit detailed or confined work, while broad ones exceeding 4 inches cover large flat faces faster. Some broaches have slightly curved edges rather than straight ones, allowing the mason to control the bite and reduce chatter on harder stones. The tool's name comes from its width, derived from the verb 'broach', meaning to open up or make wide.

The effectiveness of a broach depends heavily on stone type and the sharpness of its edge. Granite and similar hard stones require a sharper angle and lighter blows; softer limestone allows a blunter edge and more forceful work. A dull broach bounces off the stone and tires the worker; proper maintenance with a whetstone or file is essential. The tool has largely been supplemented in industrial settings by pneumatic chisels and stone grinding equipment, but it remains standard in conservation work and craft masonry where controlled surface texture matters.