Self-Cleaning of Cement Tile Roofs

Remove Debris

• Remove leaves, debris and pine needles from your roof regularly. Mildew and algae do not grow directly on the roof itself but settle on the dirt and debris that builds up on the roof surface. Other factors that affect moss and mildew growth on a cement tile roof are humidity, the direction the house faces and overhanging trees. Clear your roof of debris at least twice a year, or whenever you notice excessive accumulation, as well as just before pressure washing.

Pressure Washer Operation

• To clean your roof yourself, use a pressure washer set at about 1200 PSI. Most pressure washers have a system that allows you to add chemicals. In this case, use regular household bleach at 1 percent to kill the algae and moss. Protect your shrubs and plants near the roof overhang from damage from bleach runoff by covering them with plastic sheeting. Hold the nozzle of the pressure washer 12 to 24 inches away from the tile surface and spray in a steady back and forth motion until the roof is clean.

Safety Factors

• Wet roofs are slippery; wear nonslip shoes and be careful to secure your ladder before stepping onto the roof. Step on the lower third of the tiles when walking on your roof, not the top or side portions, as these places are where the tiles are weakest and where they are more likely to break. Professionals will often lay sheets of plywood over the tiles to distribute the weight more evenly.

Preventive Maintenance

• Cleaning your roof about every two years is recommended. To keep your roof cleaner longer, apply a clear acrylic primer followed by a sealer after cleaning. These products fill the tiny holes in the cement tiles and help to prevent accumulation of dirt, which in turn helps to prevent the growth of mold and algae.