What is corbelling primarily used for?

Corbelling is primarily used in construction to create an offset in masonry structures, particularly with chimneys. It involves stacking bricks or stones in a way that each successive course slightly overhangs the one below it. This technique helps in building sturdy and visually appealing features like chimneys, arches, and corbel tables. In the case of a masonry chimney, corbelling helps in directing the smoke upwards while also providing strength and support to the structure.

The other options do not accurately describe the primary use of corbelling. Reinforcing steel structures, waterproofing roofs, and insulating walls involve different construction techniques and materials that do not include the corbelling method specific to masonry. Therefore, the role of corbelling in offsetting and supporting structures like chimneys makes it a crucial technique in masonry work.