Date: October 7, 2015

The Good, the Bad and the Ugly: Concrete Scaling

Chances are you’ve seen it in one form or another.  Scaling is the general loss of surface mortar surrounding the coarse aggregate particles on a concrete surface.  Make sure you are keeping these tactics in mind to prevent this defect.

 

1.)    Order the correct mix.  Maryland, DC, and Northern Virginia are all considered climates with severe exposure to freeze thaw cycles.  With this in mind, the best place to start is making sure you are ordering the correct material with the minimum specified compressive strength.  Use 4500 psi concrete with a maximum slump of 5” and an air content of 6 to 7% for driveways, walkways, steps, and stairs that are exposed to weather.  See table 5.1 below that refers to the residential building code or ACI 332.10.

 

2.)    Finish it properly. Be careful not to overwork the surface with a steel trowel that will rob the surface of its air entrainment creating a low-strength surface layer.  Working bleed water into the surface layer and throwing the water to cement ratio off will also create a low-strength surface.  When the freeze thaw cycle occurs after the first winter, you can count on that weak surface to break off.

 

3.)    Protect it.  Allow proper curing and hydration of the concrete to take place by using a curing compound or covering the surface.  Apply a commercially available silane or siloxane-based breathable concrete sealer for use on concrete surfaces.

 

4.)    Use Traction Sand.  It is strongly encouraged that within the first year after placing the concrete, deicing chemicals, such as calcium or sodium chloride should NOT be used.

 

If the proper concrete material is ordered, placed, and maintained correctly, you can count on a good final product and no ugly scaling to occur after the first winter season.