Roof Chlorination to Clean Mildew and Algae
1. CAUTION: Both sodium hypochlorite (Chlorox) and calcium hypochlorite (swimming pool chlorine) are hazardous chemicals. Always read and follow all safety warnings on the containers. Keep out of eyes, off skin and protect children, plants, pets and automobiles. Work only in a well-ventilated area wearing gloves and eye protection. If any chlorine agent or mixture gets on your skin or eyes, rinse off immediately and thoroughly with plenty of clean water. Always be careful when working on roofs.
2. Before beginning, cover or saturate plants and lawn around the house with water. This will help the plants from absorbing the chlorine solution.
3. Mix one gallon of regular over the counter Chlorox (5.25%) plus 1/4 cup of TSP (trisodium phosphate) with 1 gallon of water. This 1 to 1 mixture is because over the counter (Publix, Winn-Dixie, etc.) Chlorox is a low concentrated solution (5.25%). Pool Chlorine from a Pool Supply Store is normally a 20% solution and can be mixed 1 gallon to 3 gallons water with ½ cup TSP. Test an area first as more chlorine may be needed depending on the severity of the mildew.
4. Apply one of the chlorination mixes described in step 3 to the roof at a rate of 1 gallon per 100 square feet with a garden sprayer and allow to remain on the roof for 15 – 20 minutes. Apply to the entire roof, not just visibly mildewed areas. If some areas are still dark after 15 -20 minutes, scrub with a soft bristle brush and reapply the chlorination mix.
5. Thoroughly rinse off the roof with clean water using a garden hose or a pressure washer. If a pressure washer is used, keep the pressure low (below 1500 psi) to avoid damaging the roof. Always rinse from the top of the roof down to avoid pushing water under tiles or shingles.
6. Thoroughly rinse off shrubs and lawn after treating the roof to avoid damage to the plants.
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