Concrete has seemingly endless advantages, but it does have two disadvantages: it cracks and stains. Concrete can crack if it does not cure properly or if it is too long (the reason why sidewalks have the lines is to control cracking), both problems not encountered in countertop making. Staining is a problem, however. The best way to prevent staining in concrete counters is simple: keep it clean. After foods or drinks get on the counters they should be wiped up. Things like oils, if left on the counters for long periods of time, can stain counters. The harshest elements on concrete are citrus and acidic foods (i.e. lemons, limes, vinegar, etc. and foods that include them like mayo and BBQ sauce). They don't stain as much as etch into the concrete (like marble) to change the appearance. These should be wiped up immediaetly. Counters should be cleaned using a neutral pH cleaner and should never use abrasive methods or acidic/caustic cleaners. Waxing your counters every few month or so with a carnuba based wax is a fast, easy way to keep your counter looking enriched and clean. Highly-used counter areas such as that near the main sink should be waxed more often and sealed every few years, though some people choose to not re-seal their counters and let the counter age naturally. Outdoor concrete pieces may have to be resealed after a period of years depending on usage.