Expert: Roger Zona - 9/22/2008

Question
We had colored concrete poured on Friday, September 5th (in Minnesota).  Now, some 2+ weeks later, I still see dark/glossy spots in some areas and the rest of the area seems to be lighter (like we expected) and non-glossy.  The vendor used a sealer and power washed the cement the next day when he cut it.  He came out again to seal it again 2 weeks later in hopes of fixing the problem.  I spoke to him today and he says the spots are due to the curring and it could take 30 days or more (because it's cooling off here in MN) before the spots disappear.  Is that accurate information?  I don't want to pay him before I know that it looks good, but I'm not sure I can wait another two weeks.

Answer
Kristi,

There are two ways to create colored concrete - add color at the batch plant and add color to the surface of the freshly poured concrete.

I am in Palm Beach, FL and we rarely add color at the job.  We prefer the color mixed from the plant.  The color should be added with the cement mix - in a power form - and given a very thorough blending to mix the color dye completely.  From the description of your concrete, it sounds as though the color may have been added to the truck after the concrete, aggregate and water was already in the truck.  If it was a short run from the batch plant to the job it could result in the dye not being adequately blended.

Have you had someone from the batch plant look at the job?  Ask them how the dye is added.  Also, weather could play a part in the problem and it would be reasonable to give it a chance for exposure to the sun and conditions to become uniformly colored.  He may have jumped the gun on sealing the concrete.  The concrete cures to it's ultimate strength in 28 days.  A substitute cure could be to apply a concrete "stain" - in a slightly darker shade to obtain a uniform color.  Concrete stain is a penetrating product but since he sealed the concrete, it may not work.

I would suggest you make it clear to him and the concrete supplier that the job is not satisfactory and you will pay for the work when it is properly completed.  If you ordered green concrete, you should not get polka-dot green.  If the contractor is difficult he could file a lien against your property which can be a nuisance.  Did you get a Notice To Owner from the concrete supplier?

I hope this has been useful.

Roger