How to Fix a Spalled Driveway
Spalling caused by freezing and thawing and deicing chemicals leaves
ugly pits in a concrete driveway.
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 and deicing 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. Deicing 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. Deicing 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. Once the overlay cures, apply a waterproofing sealer to prevent the problem from reoccurring.
Visit http://www.concretenetwork.com/ for more information on thin-section overlays that can be used on exterior surfaces. For more information about the effects of deicers, read this tech sheet from the Portland Cement Association: Winter Weather, Deicers Need not Damage Concrete. [Link to http://www.cement.org/tech/pdfs/DeicerPL874.pdf]
3 Comments:
is there any surface prep that needs to be accomplished before the overlay can be applied
By Nathan, at 12:45 PM
I recently had a new slab poured in my basement with radiant heat installed. The cement contractor did a bad job and the surface is sandy in some areas and ridged in others. I intended to acid stain it and polish it, but I'm not sure I can now. Is there anything I can do (short of breaking it up) to repair the problem? Will a hardener fix it? Or should I acid stain, then grind it, then apply a hardener? I'd like to avoid pouring more on top, as well, since that would raise the floor too much.
By Anonymous, at 8:26 AM
Have you considered using a microtopping? Perhaps, if necessary, you can grind any large ridges or even some light surface chipping- to constrain the profile before applying a microtopping. I prefer something like ARTEX CD, as I like its adhesion ( no primer necessary) and workability. A Small bag usually covers 80 Sq.ft. if tightly troweled out. May be broomed also.
By Robert, at 6:27 AM
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