Cracked "Quickrete" patch?

I just fixed a broken corner on my concrete steps with (2) of the small Quickrete containers. It is quick setting material, and the temperature is 60 degrees and dry. I shaped a beautiful corner and it formed nicely.
Then...about two hours later I noticed vertical and horizontal cracks in the patch. One railing leg goes into the patch, but no one went near the railing. How could it crack that soon? It was even still the dark gray color for the most part.
I'm so disappointed about this. I thought I did very well, but now I don't know what to do. Does anyone know how/why this happened??
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Dave in Minneapolis
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It sounds like shrinkage cracking.
You need to have lots of water in the original concrete or it will suck the moisture out of your patch. Once formed and finished, keep it wet. This could be done by keeping a wet towel on the patch for the first 3 days. Keep adding water to keep it wet.
I assume you used something that had bonding agent in it. The fact that there is a railing leg in the patch sounds like you won't win in the long term unless you brace, relocate, or otherwise take the pressure away from the area. You're hoping to get a patch to stick, it will never support the rail.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing. . . . DanG

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The product was never designed to do what your trying to do. Try looking for a Elmer's glue looking product for concrete. It will bond the new to the old maybe better. Try again when it is warmer. Frame under the patch and around the patch. Cover with a wet cloth for at least 24 hours. Lastly barricade the porch, top and bottom. Any vibration when setting will cause problems. Remove the railing from the concrete until it is set. It has a different temp coefficient than the concrete.
Just suggestions. Me thinks your not going to get it patched.
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