Dusting

Summary

Dusting - is the formation of powder on the upper surface of a concrete floor due to the disintegration of the top layer of material.

Technical Information

Dusting occurs when a concrete slab has been constructed in a way that leaves the concrete weak at the wearing surface. Because the concrete is weak, it is very easy for small particles of the paste to become debonded from the main body of the slab, forming a layer of dust on the surface. Heavily trafficked areas will be worst affected by this phenomenon.

Dusting can happen when the following mistakes are made during slab construction:

When the floor is finished whilst it is still bleeding or there is bleed water still on the surface. The water will be worked into the concrete, locally increasing the water/cement ratio in the top surface of the slab which will, in turn, decrease the strength of the concrete near the surface.
When the floor hasn’t been cured adequately or protected from the elements whilst curing.
When excessive carbonation of the surface occurs whilst the concrete is in its plastic state. This can be caused by the use of CO2-emitting equipment in a poorly ventilated space.
When the slab bleeds excessively, as this can cause a porous ‘skin’ to develop on the surface.

Dusting can be permanently cured by removing the weak layer of concrete with grinding. Another course of action is to apply a floor hardener to the surface, but this measure is not as effective or permanent.