Tips & Techniques

The black stains on roofs can gradually build up over time and escape a homeowner’s notice until the stains are visible from a distance. Although most barrel tile roofs are alkaline and often prevent the colonies of algae from forming, those black stains can happen, especially during the rainy season.

Baldwin Innovative Builders recommends a 1 percent bleach solution to clean moss, mildew and algae off barrel tile roofs. The solution can be sprayed on and left for five to 15 minutes to allow it to kill the organisms, after which the whole mess can be easily rinsed from the roof with a regular garden hose. Some people prefer to scrub the tiles with a wire brush, thinking that it will remove the stains faster, but the organisms will not release their hold until they are dead, and a harsh scrubbing could damage the finish on the tile. Allowing the bleach solution time to work is not only more effective, but easier as well. As long as the solution is a very diluted 1 percent, it will not harm gutters or landscaping if rinsed thoroughly. In fact, a proper rinsing can help water the plants that are close to the house.