Expert: Roger Zona - 7/13/2010

Question
Three days ago I had my patio done with colored concrete.  The patio has 12 6'x6' boxes and is going to have cement pavers border each box (the original patio was all the cement pavers and we wanted to change it up and extend it without having to throw away all the cement pavers).  My husband does concrete construction, builds forms for high-risers in NYC.  He did all the prep work for the job and we went to a reputable cement company and ordered colored concrete.  The day of delivery we had 2 guys help my husband pour the concrete into the forms and one mason for the finish work.  The mason did a broom finish & it looked great.  Unfortunately a couple hours after it was done, we had some rain, luckily we were able to get everything completely covered before when we saw the clouds moving it so the concrete was not directly hit with rain -- rain stopped, sun came back out and the plastic came off.  As each days goes by we're seeing more and more faded spots on each slab, some slabs worse than others.  The slabs that seem to get the most sun are the ones that seem to look the worst.  Faded spots, faded swirl/circle spots and faded spots that look as if it were hosed but rather than get dark from being wet, it got lighter.  2 of the slabs that get a little shade, but also have sun early in the afternoon look fine.  We have been hosing the patio every day, a couple of times a day, but like I said, as each day goes by we're getting more and more faded areas and it's starting to look like crap.  Even when we hose it, you can still see that there is some discoloration even though the slab is wet.  We are going to seal the concrete but after seeing the discoloration we're not sure what sealing is going to do to it.  I'm at the point where I may look into staining it to try and hide the faded areas.  Do you know if this is normal during the curing process?  Will it all eventually blend and if so, how long does it take?  Can I seal it while it fading or will that screw it up?  As I mentioned my husband does concrete for a living, but he's never dealt with colored concrete so we're not sure what's happening.  Any insight would be appreciated.  Thank you!

Answer
Hi Michele,
Coloring concrete is difficult at best.  For some reason I can never get a straight answer about why conditions like you described - happen!
I have always added the color to the concrete after it was poured and leveled but before final troweling.  The color is a powder that can be spread in measured amounts to get a degree of uniformity.  Concrete sets-up in three days, is partially cured in 10 days and usually at full strength in 21 days.
Since your patio is divided into 12 sections you can treat each section for the problem.  Yes,
staining is a good alternative.  Sealing the concrete may not be necessary. And, since it an outdoor area, the weather will continue to change the looks of the concrete - fading, etc.

I'm sorry I don't have a real solution.  Concrete will vary from pour to pour, truck load to truck load and batch to batch - depending on how clean the inside of the readymix truck tumbler is, how much water was added at the pour location, if the added color was the same measurement in each batch, and how much troweling is done.

I hope this has been helpful.

Roger
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