The Best Way to Waterproof a Flat Roof

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Things You'll Need

  • Paint roller

  • Trisodium phosphate

  • Push broom or pressure washer

  • Elastomeric coating

Waterproofing protects flat roofs when runoff cannot occur.

Water cannot slide off flat roofs like sloped roofs, but a simple solution exists to resolve this problem. Applying two coats of elastomeric coating protects the roof from water and also insulates the material, preventing loss of heat from inside the building. However, before applying elastomeric paint, you must measure your roof and clean it up to allow for a long lasting coating.


Step 1

Measure each surface area of your roof's length and width in feet. Multiply the total length with the total width. This gives you the surface area in square feet. Visit a local hardware store and purchase as many buckets of coating as the representative says you need for your specific roof size.

Step 2

Clean your roof with a pressure washer or broom, ensuring all the dust and dirt is removed. Use a mixture of 1 qt. of trisodium phosphate with 5 gallons of water in extreme cases to clean the roof. Wait for the roof to dry before applying the coating.

Step 3

Pour about a gallon of elastomeric coating from your bucket onto the roof and begin spreading with your paint roller. Start from a corner and work your way around the roof, walking backwards. Don't step on your coat. Repeat this process until you have covered the entire roof. Allow the finished coat to dry for 24 hours. Apply a second coat.


Mikhail Polenin

Mikhail Polenin has been working with computers since 1997. His experience also expands to astrophysics, masonry, electricity and general appliance repair. He's written about various different subjects regarding astrophysics and electrical circuits for various online publications. Polenin attended the New World School of the Arts and the University of Florida.