The sky is falling

From the Series: "Home Construction & Maintenance in Mexico"

By J. Brad Grieve, P.Eng. MBA © 2008
His Web Site

Once the rainwater drains off the roof, where is the water going?

After two strong rainfalls in Guadalajara, I was up on my father-in-law's roof last weekend to help a contractor from Chapala clean and reseal his roof. Typical of many older roofs, it showed peeling sealant, a missing base coat, mold- and mildew-stained tiles, and even a series of vines climbing up the wall and over the flat roof area. The two storey house has a flat roof area that covers the stairway, hallway, four bedrooms and two bathrooms on the upper level: a total of about 150 m2 (1,600 ft2).

After moving the stationary gas tank, it took almost six hours of preparation… yes, preparation. After clearing, sweeping, scraping, removing layers of previous sealing and waterproofing attempts, washing, performing minor repairs, raising wires/cables and, finally, acid washing, the roof surface was ready for the base coat. The final acid wash actually removed a lot of the mildew and deep seated dirt. It also helped etch the roof surface, creating a clean surface that was rough enough for the final coat to grab onto the surface.

No, we did not just seal it with waterproofing paint; we actually made up a mixture of white Portland Cement, marmolina (powdered marble), caolin (hydrated aluminum silicate) and water. After finally achieving a homogeneous creamy mixture, the final ingredient was added, which is a water-base paint sealer. The sealer is added last to prevent the formation of lumps in the mixture. Once blended, the mixture will only last one hour. All the buckets had to be applied carefully and uniformly onto the wetted roof surface.

 

To apply the coating to the roof surface was part art and part skill. It was applied using a common broom; however care has to be taken to not apply the mixture too thick or thin. If it is too thick, the mixture may crack as it dries and, if too thin, the mixture could not provide enough protection or might lift off almost immediately.

The finished product was brilliantly white and will tolerate solar exposure and not heat up much compared to darker colors (i.e. red oxide, black, green, etc.), and it was noticeably cooler inside the house since the roof/ceiling was not radiating much heat into the bedrooms.

This leads me into a couple other notes about roofs that need to be addressed during the winter dry season, before the rains of summer. First. . .

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