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Ask the Expert: “Can chlorine be used on tiles…”

Contractors are often asked about the best way to clean a tile roof.  Below is a recent question submitted through our “Ask the Expert” form and the response from TRI President and Technical Director Rick Olson.

moss on a tile roof

An extreme example of unchecked moss and tree debris on a 30-yr roof in a cool humid climate.

Question – “Our contractor suggests water blasting of tile roof to remove dirt and what I will assume is mold. Can chlorine be used on tiles or will there be a risk of streaking the tiles?”

Response – The cleaning of tiles with pressure washers is a common practice as regular roof maintenance. Since roofs are slippery when wet, the work should be performed by a qualified roofing professional. The use of diluted chlorine can be used to help remove the final algae that might be present, but we have seen just plain water used as well. The pressure washer should not be above 1300 psi as it can create surface wear. The dirt, algae or moss that grow on the surface of the tiles are not affecting the condition of the tiles. It is more an aesthetic issue that homeowners wish to remove.

2 Responses to Ask the Expert: “Can chlorine be used on tiles…”

  1. William Rahm April 21, 2016 at 12:27 pm #

    Twenty years ago, I had a cement tile roof installed on my new home in Florida. The cement tile is flat and resembles red cedar roof shakes.

    For the past 19 years, I have used swimming pool chlorine (14%) using a green container that is sold in most hardware stores and contains detergent for cleaning windows.

    The container is designed to attach to the end of a hose and puts out a stream of water 20 to 30 feet, so there is no need to climb onto most single story roofs.

    First of all, pick a calm day to clean the roof. Empty the window cleaner from the container and fill the container with full strength swimming pool chlorine.. The water from the hose, pulls the chlorine and dilutes it to approximately 2 or 3 percent at the nozzle.. I can usually reach the peak of the roof by using a ladder that is placed near the edge of the roof. Wet approximately a 20 to 25 foot foot wide area of the roof, starting at the top of the roof and working your way down to the edge of the roof with the diluted chlorine. Let it set while you move on the next section of roof. After wetting down the second section of roof, turn the valve on the container to “rinse”, Go back to the first section and rinse the roof with clear water. It generally takes about 3 hours to clean the entire roof on my 2000 square foot house.

    Recently I have tried leaving the diluted chlorine solution on the roof and not rinse the roof with clear water.. It appears to work just as well with no difference in the appearance after the roof has dried.

    Bill.. Lady Lake, Florida

  2. Lisa April 26, 2016 at 10:09 am #

    Hi Bill, Thanks for sharing your comments.