Short answer
Tool choice follows how the material breaks, not how hard it is. A moil point penetrates and cracks from within; the general-purpose answer. A chisel breaks along a line and earns its place in reinforced concrete, layered rock and directional breaking. A blunt tool does not penetrate at all; it transfers energy to the surface and wins in secondary breaking of hard, brittle rock. A pyramid sits between moil and blunt and lasts longer in abrasive material. On most sites a moil goes on and never comes off; the most common and most expensive habit there is.
Start with how the material breaks
The first question is not "how hard is this material" but "how does it fail". Brittle material (hard limestone, granite, well-cured concrete) fails by crack propagation: a crack starts at one point and runs. Material that behaves plastically (clay soils, frozen ground, some asphalts) does not propagate cracks; it flows around the tool.
In brittle material, concentrating energy at a single point works, because starting the crack is enough. In plastic material you have to spread the energy and tear the material away. That distinction is why four tool shapes exist.
Four shapes, four different jobs
- Moil point: penetrates and cracks the material from inside. It has the widest field of use and is the first choice in mixed material, excavation and general demolition. Penetration is high, but because the point is small, wear concentrates there.
- Chisel: breaks along a line. It wins in reinforced concrete walls, slab cutting, layered rock and any directional breaking. Blade orientation matters: it is aligned along the line you want to open, not across it. A cross chisel breaks in two directions at once.
- Blunt: does not penetrate; it transfers energy over a wide face. In secondary breaking of hard, brittle rock (sizing oversize blocks in a quarry) it is the most productive tool. Because it does not penetrate, the risk of sticking and jamming is low.
- Pyramid: a geometry between moil and blunt. It keeps some penetration while spreading wear away from a single point, giving longer life than a moil in abrasive material.
Which one wins where
- Mixed excavation, foundation digging, general demolition: moil.
- Controlled cutting in reinforced concrete walls and slabs: chisel.
- Layered, bedded rock (schist, bedded limestone): chisel, oriented to the bedding.
- Sizing oversize blocks in a quarry (secondary breaking): blunt.
- Hard, brittle and abrasive rock over long shifts: pyramid or blunt.
- Frozen ground, clay and plastic material: moil; a chisel jams in this material.
- Asphalt removal: chisel, the wider blade preferred.
The most common and most expensive habit
On most sites a moil goes on the breaker once and never comes off. The moil really is the most general-purpose tool, but it cannot do what a blunt does when sizing oversize blocks in a quarry: it penetrates, jams, bends and wears out in half the time. Changing a tool costs half an hour; working with the wrong one costs both tool life and shift output.
Chisel orientation: the detail most often missed
A chisel blade faces one way, and that direction changes the result directly. Aligned along the crack line you want to open, the material separates along that line.
In bedded rock the logic differs: held parallel to the bedding plane, the tool enters between the layers and levers them apart. Held across them, the same energy does far less work.
Blade direction is fixed by the retaining pin when the tool is fitted; a chisel free to rotate changes direction with every blow and loses the entire advantage of being a chisel. That is why the condition of the retaining pin matters at every tool change.
Before changing tool type, check it is not the breaker
When output falls, the tool shape is not always the culprit. Falling nitrogen pressure, insufficient oil flow or a worn bushing all produce the same complaint: "it does not cut like it used to".
The order should be: first, is the breaker itself healthy (pressure, flow, tool play); second, is the tool type right; last, is the tool worn. Skip that order and you buy a new tool, the problem stays, and the money is gone.