Efflorescence Hides Integral Color

Where’s the color? On the left side of this integrally colored pool deck,
it’s masked by a thick layer of chalky efflorescence.

Question:
What would cause half of this integrally colored concrete pool patio to look so washed out? The ready-mix supplier claims to have put color in the mix, but the finisher claims to not have seen any color when placing the load. Is there any way to determine if color is actually in the concrete?

Answer:
Because so many factors can affect the appearance of concrete—when placing the mix as well as after the concrete is in place—an internal sample is the only sure way to determine the presence of color throughout the concrete slab. In this case, a core sample was required because the slab is above grade and surrounded by walls on all sides, although taking cores is usually the last resort because of the cost and the hole it leaves behind in the concrete. (The same information can be obtained nondestructively by looking at a scrap piece or retained sample of the concrete.)
The core sample from this pour shows that color is indeed present throughout the slab. This means that something affecting the surface is causing the off-color. Further investigation found that the pale areas of the pour where placed at a different time. These areas also have a blotchy white surface effect, known as efflorescence—a calcium carbonate residue that leaches out of concrete over time. (I’ll cover the causes of efflorescence in more detail in another Q&A). When too much efflorescence exists, it can totally hide the true color of the concrete.

Mild acidic cleaners or specialty cleaners for efflorescence are the best way to remove the white, chalky substance. Following up with the application of a sealer is always a good idea, since efflorescence can return if moisture gets into the slab, starting the chemical reaction all over again.