What cases spalling?  This is a common question we get asked for example.

Question:

What caused this surface failure on my integrally colored concrete driveway, and what can I do to repair it? The driveway is 6 years old and 1,000 square feet in size, but only a few hundred square feet directly in front of the garage doors show signs of failure.

Answer:

This type of surface failure, known as spalling or scaling, is more common in colder climates where freeze-thaw cycles (we see approximately 50 of these annually in Alberta) and de-icing chemicals are prevalent. Freezing causes the water in the capillaries of the concrete to expand, creating pressure. Over time, the expansive pressure from repeated cycles of freezing and thawing can break away the top surface of the concrete, leaving pit marks and exposing the coarse aggregate. De-icing chemicals only aggravate the already-stressed concrete by allowing more water to migrate into the concrete, thus increasing the size and depth of the spalling failures when a freeze occurs. That’s why the problem occurred only in front of the garage, where the cars are often parked. De-icing chemicals picked up from the road dripped onto the surface, allowing water to permeate that area.

On new concrete, you can dramatically reduce water-induced spalling by applying a penetrating waterproofing sealer 28 days after concrete placement and every few years thereafter. To address the problem after it has occurred requires covering the entire affected area with a polymer-modified cementitious overlay in a color matching the existing driveway or a new pattern and colour. Once the overlay cures, We apply 2 coats of a waterproofing sealer to prevent the problem from reoccurring.

We see these commonly in garages as well; although the problems are caused by the same de-icing agents falling on the floor the fix is a little different.  We never recommend using sealers in doors because of off gassing and it is very slippery, even with the traction aids.  We can fix spalling in garages by hand troweling an epoxy motor mix into the spalls and then grind it flat.  The garage floor can then be coated with an epoxy coating and the problem will not happen again..