Concrete, in and of itself, is rarely beautiful. Making it something other than a dreary expanse of gray depends on you. The first thing to realize before beginning to paint concrete, however, is that all concrete is not created equal. Some of it presents a surface that is smooth and rigid; in other cases, older concrete might be pitted and porous.
Thus, traditional paint is sometimes the wrong covering to use for concrete. Stains specific to concrete have filled a niche in the paint industry, even as they penetrate and fill niches in the surface they're designed to cover.
Nevertheless, that penetrating power is a mixed blessing. Unlike concrete paint, a concrete stain is forever. Some varieties even form a chemical bond with the concrete itself. Therefore, a decision on what color to stain a concrete surface has to be a final one.
If you decide to paint concrete, you will have the opposite problem: a tendency for the paint to separate from its surface over a short period of time, especially in high traffic areas. Experts on painting or staining concrete recommend that color not be applied until the surface has had at least a week -- and, according to some, as long as 28 days - to dry and cure. Curing compounds have been developed to accelerate the setting and drying processes. The problem is, these compounds can often keep paint from properly adhering.
One solution to this is acid etching. After a surface has been cleaned of dust and grease (with a power washer, if necessary) and washed with a cleansing solution, a diluted solution of muriatic, phosphoric or sulfamic acid is applied, generally with a mop or spray unit to avoid contact with the skin. This solution will produce a rough surface more receptive to paint or stain.
Moisture is the primary enemy of painted concrete floors. If areas of seepage aren't dealt with before the paint is applied, water will build up beneath the paint and cause it to blister. Application of a sealer is the most direct way to respond to this problem. Once this is done, certain types of paint will "breathe" to allow the moisture to evaporate.
There are literally dozens of types of paint and stain that can be used to paint concrete, from bright colors to earth tone stains that give the concrete a natural look. Epoxy paint is another viable option.
It is generally recommended that several coats of paint be applied in thin layers to make sure the irregular areas are properly covered. To paint concrete (or stain it) takes a lot of work, in other words. But the alternative is gray.