Scabbling (also called chipping or hacking) is the mechanical roughening of a concrete surface by knocking small pieces out of it, so that a newly applied layer bonds better. The result is a rough, open surface with sufficient grip for the new material.
Why scabble?
Smooth concrete provides inadequate adhesion for a new layer of concrete, mortar or plaster. By roughening the surface:
- Mechanical bond — the new layer keys into the irregularities of the surface
- Larger contact area — more bonding points between old and new material
- Removal of cement skin — the smooth top layer is removed, exposing the coarse aggregate
Application
Scabbling is used in:
- Construction joints — between two concrete pours made at different times
- Repairs — before applying repair mortar to damaged concrete
- Plastering — preparing a smooth concrete surface for rendering
- Floors — before applying a new screed to existing concrete
- Exposing reinforcement — during concrete repairs the cover is chipped away around the rebar
Methods
- Hand tools — chisel and hammer for small areas
- Pneumatic scabbler — for larger surfaces
- Needle gun — for finer surface treatment
- Milling machine — for flat, horizontal surfaces
Related terms
- Concrete
- Bonding
- Formwork
- Construction joint
- Repair mortar
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