Pattern in concrete

I am not concerned or calling the coloring pattern in the photo a defect. There are variations of this pattern on the edges of all of the porch slabs. The house is 20 years old.
Do any of you know what might have caused this pattern?


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Do you know what was used to form the concrete?

Possibly a release agent was used on the forms, and that can range from wax to oils and various other products.
That concrete does not look to be 20 years old, looks like a new pour.


Nope. The edges were rough and did not have the imprint of wood forms.

Agree, or at least “newer” pour.
I looked around at some of the neighbor’s porches and didn’t see the same pattern.
And I am a curious guy. Maybe they poured in very cold temps and the calcium created the pattern.
I took the photo when I dropped off the radon test. When I inspect the house tomorrow, I’ll take a closer look at all the concrete work around the house.

I have seen this many times before. It’s probably water stains. Looking at the surface of the landing, it was covered with plastic or a concrete blanket after it was poured. That always leaves a marbled look on the surface.
Another possibility is over application of a water based sealer after a windy day, where the surface wasn’t prepared correctly.
Would need to see clearer pictures close up. The one you posted gets blurry when blown up.

You don’t see form board markings because it was stripped and faced with a mag or sponge float when it was still wet enough to finish yet set up enough to hold it’s shape. Common practice. Saves from having to return and apply a parge coat.

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the steps are pre cast. and they have hollow sections, its the air and moisture keeping that part of the concrete a bit wet. it should go away when weather gets warmer and the concrete heats up.

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Temperature, evaporation, and how water disperses from the landing and decking.
Think of it as Ghosting pattern.
PS: The poured concrete are solid slabs.

From some type of cleaning of the concrete surface(s) - Possibly Acid washing of the porch and landing concrete can stain areas down along edges of the sides that weren’t totally acid washed as the surfaces were and the liquid cleaning material (acid) stained the sides / edges in streaks.

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They do look pretty clean for 20 years old…good thought, Joe.