Light scaling can be cleaned and sealed, or resurfaced with a bonded overlay. Severe scaling may need replacement. Ask a concrete contractor to assess it.
Scaling, Dusting & Other Surface Defects.
Most surface problems start on pour day. Here's what causes the common ones, and how to avoid them.
At a glance:
4 : Common surface defects
5-8% : Air content that resists scaling
1st Winter : Keep de-icing salts off new concrete
Scaling.
Scaling is flaking or peeling of the finished surface. It usually starts in small patches after freeze-thaw cycles and spreads.
It's most common on exterior concrete without enough entrained air, finished while bleed water was present, or not cured properly. Use an air-entrained mix for all exterior flatwork. Keep de-icing salts off during the first winter, and never use fertilizer or ammonium-based de-icers on concrete.
Dusting.
Dusting is a soft, powdery surface that rubs off under traffic. The surface layer is weak, usually because water was worked into it during finishing, it dried too fast, or it was exposed to carbon dioxide from unvented heaters in cold weather.
Prevent it by finishing only after bleed water is gone, curing promptly and venting heaters outside any enclosure.
Blisters.
Blisters are small bumps where a thin skin of mortar has sealed over trapped air or water. They form when the surface is closed too early, often in wind or sun, or with a hard trowel finish on a sticky mix.
Delay final trowelling until bleed water and trapped air have escaped. Avoid over-working the surface.
Delamination.
Delamination is when a thin surface layer separates from the concrete below. It often sounds hollow when tapped. Like blisters, it happens when the surface is sealed while the concrete underneath is still bleeding.
Avoid hard steel trowelling on air-entrained exterior slabs. A broom finish is the standard for exterior work.
Frequently Asked Questions
Can scaled concrete be repaired?
Are de-icing salts safe on concrete?
Keep them off for the first winter. After that, plain rock salt used sparingly is generally acceptable on well-made air-entrained concrete. Avoid ammonium-based products.
Will a sealer prevent scaling?
A penetrating sealer helps by keeping water and salt out. It can't fix concrete that lacks air entrainment or was finished poorly.
Surface hardeners can treat light dusting. Severe dusting may need grinding or an overlay.
Why is my slab hollow-sounding in places?
Usually delamination or curling. Mark the areas and have them assessed before applying floor finishes.
Disclaimer: These guides are general information. Always follow your engineer's specification and local building requirements.
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