There are two primary methods used to color cement. One is a dry pigment that is swept across the surface of freshly finished concrete, and the other is uses powder or liquid pigments that are mixed into the wet concrete before it is poured. The first method is quite easy to do but has the disadvantage of being easily chipped. For small projects, the mixed method is probably the best solution, while surface coloring is great for large areas. For really large jobs, you can get pigment added to the batch when it is dispatched from the concrete yard.
Method 1 - Surface Coloring
This method requires that the concrete has been poured and finished, but should still be "wet."
Sprinkle on the Powder
As your concrete is curing, cover the area with an even coat of the colored powder. Avoid clumping the powder as it can become difficult to clean. If the area is small enough, you can apply the powder by hand. Be sure to wear gloves if this is your preferred application method. For larger areas, you can use a style bar spreader. You want to apply approximately 2 pounds of powder pigment per square foot, though you should check the manufacturer's instructions for a more specific measurement.
NOTE: For more vibrant results, use two applications, applying 1 1/3 pounds in the first coated application and applying the remainder in the second application.
Broom Finish the Concrete
Broom finish the concrete. Sweep the surface evenly, so that the powder covers the surface uniformly. Apply slightly more powder to areas that are too thinly covered.
Let Powder Set
The first application of powder should dwell on the concrete surface until internal water absorbs the pigment. This will likely take 24 hours.
Rinse the concrete with a garden hose to remove excess powder.
A sealant or finish is applied to the first application of the pigmented powder. You'll want to be cautious that you apply the finish gently so that it does not break through to the gray-colored concrete. Let your sealant dry as the manufacturer instructs.
For a more vibrant look, apply the remaining 2/3 pound of pigment to the concrete and repeat the entire process.
NOTE: You'll want to hose the concrete down after it has finished drying fully from the sealant application and before applying the second coat of powder so that the powder has something to absorb when applied.
Method 2 - Mixed Coloring
This method involves mixing concrete with added pigment. Pigments usually come in small boxes or bottles. Quikrete makes a 10-ounce cement dye that mixes with 2 60# or 80# pounds bags, saving you the trouble of calculating the tint yourself.
Mix the Concrete
Add 2 bags of concrete mix plus any sand required to complete the mixture to a wheelbarrow or cement mixer. Mix the sand and concrete well before adding any water. Then mix the dye with 2 quarts (1/2 gallon) of water and add the colored water into the concrete mixture. Be careful that the entire mixture is well turned so that the color is evenly distributed.
NOTE: For larger surfaces, you can use more bags of concrete, more dye, and more water; you just have to be sure that you've done the correct calculations to multiply your needed materials.
If you will be applying the concrete as a coating over an existing surface, add 1/2 cup of bonding agent for every bag of concrete used.
NOTE: A bonding agent may cause the concrete color to be slightly lighter in shade than you originally planned for.
Apply Concrete Mixture
Apply your mixed, pigmented concrete with a trowel and allow it to set.
To get a multidimensional finish, mix the concrete with one uniform color, using a complementary color to add lashes to the mix. The concrete will dry with the second color mixed randomly, providing an interesting effect.
NOTE: Only mix complementary colors in lightly.
For a multi-colored pattern, use wooden cut-outs, and dip them in dry powder colors before "stamping" the pattern on wet concrete.
Notes on Concrete Coloring
Surface coloring can be removed with some patience and muriatic or hydrochloric acid, but mixed colors are permanent. Before you add colors, look at a sample of how the pigmentation performs if possible. The unmixed color is usually darker than the mixed one will be, but manufacturers differ.