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Colored Concrete Q&A

Above picture shows how Pavers are much easier and to maintain and keep looking perfect. For those who insist on colored concrete, here are some frequent asked questions and yes we clean ‘n seal a lot of concrete as well.

Efflorescence occurs with all concrete and is the most frequent problem that concrete contractors face with colored concrete.

Efflorescence is caused when soluble salts and other water dispersible materials come to the surface of concrete and mortars. It’s induced by low temperatures, moist conditions, condensation, rain, dew, and water added to the surface of fresh concrete to assist troweling.

Any material containing portland cement results in efflorescence. The most usual reaction occurs when calcium hydroxide (lime) formed in the hydration reaction of portland cement (approximately 140 pounds per cubic yard of concrete) is transported by water to the surface through capillaries in the concrete.

Efflorescence is normally white and shows up more on darker colors than white or light gray because of the contrast. Only 0.2 ounce of calcium carbonate per square yard of surface is needed to cause a significant shift in color. Some forms are very difficult (if not impossible) to remove, while others are easy—especially if they are removed right after they form.

After acid washing, slabs should be rinsed thoroughly and neutralized with baking soda (sodium bicarbonate) or an equivalent. Acid residues can harm plants. The reaction products of acid on concrete are all soluble calcium and iron salts, which can cause more efflorescence.
When efflorescence can’t be removed with acid washes, other commercial products are available. One is ethylenediamine tetraacetic acid (EDTA), which rapidly dissolves calcium salts. EDTA will also damage concrete, so it’s best to test it on an inconspicuous sample area first.


Question:  I went to my local hardware store and the salesman said to wash my concrete with muriatic acid. It removed the glue but when I went to stain the floor I did not get a color reaction. What happened?

NEVER wash the concrete surface with muriatic acid if you plan on acid staining the concrete slab.  The muriatic acid will deplete the lime in the concrete and will roughen up the surface.  The Kemiko Stone Tone Acid stain needs to react with the lime in the concrete and if that is removed, the stain will not color the concrete.


Question:  My stain is not getting a reaction with the concrete, Why?

This issue can be caused by various reasons. These reasons vary from how smooth or tight the surface is troweled to something spilled onto the concrete. Does the concrete contain add mixtures that were added to the concrete mix like fly-ash or slag?  Was a curing sealant added to the surface to help in the curing of the concrete surface?   All of these issues can have an effect on the concrete accepting the stain.  To find out if the surface is too smooth you can spray water on top of the surface.  If the water soaks into the concrete, the stain will most likely do the same.  If  it “beads” up on top, the stain will “bead” up also and will not penetrate the surface and react with the lime in the concrete.  This can usually be fixed by sanding the surface of the concrete with a sanding screen, black pad (sometimes), or 100 to 120 grit sandpaper. This same technique can work to remove the cure and seal.  To find out if sanding or abrading the surface will help, try sanding a small section by hand, and see if the pores open up and accepts the stain.  Do this in the most unnoticeable area of the floor, since it will be hard to blend that test area in with the rest of the stain process.

Question: How much does the gallon of stain cover?

This product is mixed 1:1 water to stain and will cover approximately 400 sq. ft. in 2 coats or 800 sq. ft. 1 coat.  It is recommended to apply the stain with 2 coats.

Question:  I like the color that I achieved with the staining process, but there is a small section that did not stain. How can I fix this?

This can be caused by something that was spilled onto the floor by the builders or previous owner and can be fixed with a couple of techniques.  Try to brush the stain into the area with a nylon or a chip paint brush first at 1:1 with water and if that does not work try using the stain full strength.  Sometimes sanding the floor with 100 grit sandpaper will open up the pores of the concrete and allow the stain to react.  If the stain just will not get a reaction with the concrete you can try using Kemiko concrete dyes.  The dyes are available in both solvent based and water based systems. Both can be applied to the surface after the reactive stain has been cleaned and neutralized.  After  step 3 has been completed and the surface is dry apply the Kemiko concrete dye to the surface and let dry. After the desired color is achieved, let dry the recommended time and apply your sealer of choice.  When using the dyes, there is no need to neutralize after application.

Question: I stained my floor two years ago and want to change the color. How can I do this?

This can be done by removing the sealer and applying more stain to the floor. You can only make the floor a darker color, not a lighter color.  One can apply a micro-topping (a thin layer of modified concrete) to the surface and start over.  This will allow for a new color to be applied to the floor. Micro-toppings are an easy way to prepare a floor surface for concrete staining that normally would not accept a stain.