Concrete statues are an investment in beauty, and if they begin to deteriorate, it's frustrating. In cold weather cracks allow moisture in, which will freeze and expand, thus widening the cracks, so when grime accumulates and cracks begin to riddle a statue's surface, take action to protect your investment.
Gather a scrub brush, alkaline cleaner (available at hardware stores or you can make your own), and a bucket of hot water and take them to the piece that you plan to restore. If the statue is small enough, bring it to the hot water source, rather than the other way around.
Spray the cleaner onto a portion of the surface of the statue and let it sit for a few minutes. Use the brush to scrub away any soot, grime or mould. Continue this process until you have cleaned the entire statue. If necessary, repeat. The statue may not return to a new appearance, but it will look much better.
Mix an appropriate amount of Portland cement with a small bit of water in a throwaway plastic container. The substance should have the consistency of grout.
Make sure cracks are free of any loose bits of concrete or dirt and dampen them with water.
Apply grout with the putty knife. Smooth off with a wet finger. Let dry for two hours.
Moisten the repair with a mist of water and cover with plastic wrap. Keep it covered for five days, lifting the plastic and re-moistening the repair each day.