Need the right tools Roy.
By using various bushing tools with your pneumatic hammer, it is possible to rough out, finish carve and texture many types of stone. This valuable stoneworking technique not only saves time, but also produces a wider variety of surface finishes than is possible with conventional hand tools.
Some important things to remember:
Do not hold onto the bushing chisel. Hold the pneumatic tool perpendicular to the stone so the chisel moves freely, bouncing and spinning over the surface in a random pattern (called “dancing”).
The 4-point chisel (above left) is ideal for roughing out your work and will leave a course texture. The 9-point chisel (center above) removes less material but leaves a finer surface. The cup chisel (above right) will not dig and is excellent for curved areas; use it to achieve a smoother texture prior to final finishing.
In my case, I used a diamond tip bushing head on a Hilti electric hammer drill set on drilling and hammer mode. This spins the bushing head around instead of direct impact.
The cause of the de-layering was initially due to the process of over thermal.
Granite like many other stones, undergo a process of smooth glossy finish, a honed finish where the stone is smooth and not glossy, and the thermal finish which is used for steps and what not. This process is done with an external flame and roughens the surface to give it a texture.
During this process, if the external heat applied is to hot, it will layer the stone as shown in my previous post.
Bushing down the stone with the right head, can bring the stone back to it’s original state and harder layer of the stone matrix.
Hope this helps a few.