Scabbling—also called scappling—is the process of reducing stone or concrete.
In masonry, it refers to shaping a stone to a rough square by use of an axe

Axe

The axe, or ax, is an implement that has been used for millennia to shape, split and cut wood; to harvest timber; as a weapon; and as a ceremonial or heraldic symbol...

 or hammer

Hammer

A hammer is a tool meant to deliver an impact to an object. The most common uses are for driving nails, fitting parts, forging metal and breaking up objects. Hammers are often designed for a specific purpose, and vary widely in their shape and structure. The usual features are a handle and a head,...

. In Kent, rag-stone

Rag-stone

Rag-stone is a name given by some architectural writers to work done with stones which are quarried in thin pieces, such as the Horsham sandstone, Yorkshire stone, the slate stones, but this is more properly flag or slab work. By rag-stone, near London, is meant an excellent material from the...

 masons call this "knobbling". It was similarly used to shape grindstones.

In modern construction, scabbling is a mechanical process of removing a thin layer of concrete from a structure, typically achieved by compressed air

Compressed air

Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....

 powered machines. A typical scabbling machine uses several heads, each with several carbide

Carbide

In chemistry, a carbide is a compound composed of carbon and a less electronegative element. Carbides can be generally classified by chemical bonding type as follows: salt-like, covalent compounds, interstitial compounds, and "intermediate" transition metal carbides...

 or steel tips that peck at the concrete. It operates by pounding a number of tipped rods down onto the concrete surface in rapid succession. It takes several passes with the machine to achieve the desired depth.

Scabbling is used to remove road markings, surface contamination

Contamination

Contamination is the presence of a minor and unwanted constituent in material, physical body, natural environment, at a workplace, etc.-Specifics:"Contamination" also has more specific meanings in science:...

 (used in the nuclear

Nuclear power

Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...

 industry), to add a decorative or textured pattern to concrete, or to prepare a concrete surface prior to the installation of grout

Grout

Grout is a construction material used to embed rebars in masonry walls, connect sections of pre-cast concrete, fill voids, and seal joints . Grout is generally composed of a mixture of water, cement, sand, often color tint, and sometimes fine gravel...

.