I drew up some front steps for a bungalow to be poured between two brick parapet walls. The contractor seemed thorough and conscientious, and was a nice guy to boot. I wasn’t there for the pour, but it passed a pre-pour inspection, and from what I could tell, there was good rebar where it ought to be, and everything seemed to go smoothly. The steps were poured about July 10th, 2010 (see pictures). As of February 2011, the concrete was spalling all over- on the landing, every step, and the panels in front of the steps.
We are just north of Chicago, and we get the extremes of weather, including this year’s Groundhog Day blizzard, followed 10 days later by temps in the high 60s, followed by more snow. The homeowner had been using salt on his steps during the snowy and icy weather- the same bag of ice he’d used for years before on his old steps with no problems. The homeowner called the concrete contractor, who said the problem was that he used ice on the concrete too soon. We have no memory of him warning us not to use salt on the steps in the first winter, but also I would think that if not using salt in the first winter were the custom, that would be general knowledge available to me and the client. I don’t know if he mixed his own concrete or got it from a supplier, but it’s just these steps and a short walkway, so I don’t think there was a big truck. Meanwhile, there is a walkway in the back of the house that the same concrete contractor poured a few weeks later, and that concrete looks great. That concrete didn’t get any salt sprinkled on it, so it’s not a great comparison, but it still suggests to me that there was something wrong with the first pour, either in the mix or the finishing.
Does anybody have any ideas as to what the reason for the problem might be, and what a fair remedy might be? Should the guy jackhammer down to the rebar and re-pour the top 2 or 3 inches? Thanks.
Replies
Temperature
I seem to remember it being hot about then, there.
If concrete starts to cure, and is worked after it sets, you can get a surface that looks good, but isn't properly cured. It dries out as opposed to hydrating, and is weaker, and more susceptible to damage than properly cured concrete.
Salt should not be used on concrete the first winter or two, and one should go easy with other ice melters, even those that claim to be safe. This is one of those things that "everyone knows" around here. Generally after 3-4 years concrete is reasonably immune to moderate amounts of salt.
Of course, spalling can be due to a number of other things -- wrong mix, worked too hard, set when it was too hot, not cured properly. Hard to assign blame.
Depending on the cause and severity, spalled concrete may be repairable without having to resort to a jackhammer. I'm certainly no expert, but I've resurfaced our front porch using products from Menards, and it turned out reasonably well. A skilled mason could no doubt do much better.
salt
Salt should not be used on concrete.
The newer the crete, the worse the damage
If the crete is not well sealed, the damage is worse
If the crete was finished to hot, too cold, too wet, or too soon, more spalling is expectd
Concrete test
Thanks. The contractor says he is going to come out and test the concrete. Do you know- is there such a test that would really tell us anything?
I think my steps have been taking salt for 64 years now, and they still look like new, no cracks or anything. I just checked, and it looks like our current salt supply is actually kosher- could be the steps were blessed by a rabbi during the pour, who knows.
As was said before, concrete is particularly sensitive to salt the first year or two after it's poured.
I think Jigs is on the right track. Did the concrete "dry" or was it "cured" (covered and kept wet for at least a week)?
If the top of the concrete dries out before it cures, it will spall off the first time it freezes.