Expert: Roger Zona - 3/26/2007

Question
QUESTION: Last year I hired a local concrete guy to come and do the steps up to my house and the sidewalk in front. He did this in two sections, half the sidewalk in one and the other half and the steps int he other. He wa svery late getting to it and the first half was poured in early november. The last part he didn't get to until mid december. He assured me that he had extra cement added to it, and he covered it with blankets to keep it warm. It got very cold here shortly after, and the blankets were removed after the snow and ice was gone (two weeks). The surface appears blotchy now, like it's a different color where the blanket was touching it and lighter where a wrinkle might have been. It looks very different from the other part of the sidewalk. I have asked a different contractor in the area if it could have frozen, and he said it would have already been spalling if it had done that. What is causing my discoloration though? Is there anything I can do about it?
ANSWER: Dear Michael,
Concrete in the winter can be a problem.  Adding extra cement is not necessarily recommended.  More concrete is added for additional test strength.  He should have added an add-mixture of anti-freeze.  This is common for pours that may experience freezing.  It slows down the evaporation of water and prevents the water from freezing and spawling.
As for the discoloration - there are several good concrete "Stains" on the market.  Not a paint, which stays on the surface but a penetrating stain.  It comes in many colors including gray if you want the concrete to look like concrete.  Another method may be to acid wash the walk or use a concrete cleaner.  This method may not give you the best results and is more commonly used when concrete gets stained by oil or paint.  Contact your local concrete plant and they can give you some help about stains, cleaners, etc.
I hope this has been helpful.

Roger

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QUESTION: Are there any long term effects of this?
ANSWER: Michael,
I don't quite understand what you mean by "long term effects".  Concrete will change with age and weathering but that will take some time.  Concrete is a natural product and "what you see is what you get".  To get a more uniform color, the best solution is concrete stain.  You can even create a pattern on the walk.  Using a clear wax marker, draw a stone pattern and use two or three stains in the same color family.  The wax leaves a "grout" effect.  
Good luck.

Roger

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QUESTION: Roger -

Sorry. I should have ben more specific. Do I need to worry about it spalling or otherwise having a shortened life because of this? If it purely cosmetic it's not that big a deal to me - the stain I may do to it.

Answer
Michael,

Perhaps - because next winter it will freeze again and if there are any weak spots in the pour, the annual freeze/thaw could do further damage.  Does the pour have any reinforcing such as wire mesh or steel bars?  Reinforcing will help to keep the concrete solid but you could still have spawling from the constant changes in weather.  Hot summers cause the ground to move slightly and this could effect the walkway.  Also, I assumed the installer cut-in expansion joints.  The joints are really control points for cracking.
I guess what it really boils down to is the quality of the product and workmanship.  Normally, the contractor would warrant his work for one year.  If nothing happens in that 1st year, he would not have any liability. However, if you have cracking, crazing or spawling during the 1st year, I would expect the contractor to replace the affected section.
Hope this is helpful

Roger