Cold Fusion

Oct. 1, 1998
As winter approaches, it is a good idea to get school roofing systems in shape for the cold. Ice damming, snow loads and freeze/thaw cycles can play havoc

As winter approaches, it is a good idea to get school roofing systems in shape for the cold. Ice damming, snow loads and freeze/thaw cycles can play havoc on a roof.

While roof inspections should be done on a quarterly basis, a pre-winter inspection is especially critical. October or November is the best time to inspect a roof in anticipation of a possible severe winter. Making minor repairs before the winter season begins will keep the school dry, and prevent major damage during the winter and costly repairs in the spring. Before repairs are carried out, however, check to see if any warranties are in place.

Making repairs Following are some problems that might show up during a roof inspection and possible solutions:

-Built-up roofing (BUR) blisters are bulges in the roof membrane that have a spongy feel. These can become brittle in cold temperatures, and may be broken easily by any foot traffic, hail or heavy snow loads. To repair the area, first cut out the blisters, and remove any dirt or gravel around them. Flashing or plastic cement with a reinforcing membrane should be used to repair the area. Application of a primer prior to the use of the cement will improve the adhesion of the mastic. Always make sure moisture is removed from the area prior to repair.

-Splits in the membrane allow moisture to seep into the membrane, and then into the school. Even a minor split can cause major leaks as the temperatures dip below freezing and ice damming occurs. Repair all splits by using two coats of flashing or plastic cement with a reinforcing membrane embedded in the cement.

-Flashings along walls or around roof protrusions also can deteriorate and should be checked thoroughly on a roof inspection for cracks, splits, separation or bare spots. These can be repaired using two coats of flashing cement and embedding a reinforcing membrane in the cement.

-Parapet walls and copings also should be inspected for possible entry points of water and moisture penetration. If the joints are cracked, they should be repainted with a suitable elastomeric caulking compound.

-Loose copings should be reset using mortar or an appropriate adhesive. Any cracks in the walls should be repainted with the proper caulking compound, or repaired by covering them with flashing cement and a reinforcing membrane.

-Pitch pockets should be inspected for any separation of the sealant from the pipes and penetrations. If any are visible, use an elastomeric trowel or caulking-grade mastic to make adequate repairs, ensuring a permanent bond between the pitch pan and the sealant.

A final inspection After all repairs are made, it is time to inspect the field of the roof surface. Pay particular attention to:

-Alligatoring of bituminous roof surfaces, which gives moisture and snow another avenue for entry into the membrane. Before the weather gets too cold, remove any deposited dirt or dust that could impede adhesion of the coating, and resurface the roof with an asphalt fibered emulsion or solvent-based fibered roof coating.

-Exposed felts and other bare spots, which are a sign of a weathered or heavily traveled roof. The exposed felts absorb moisture, and allow water to seep down into the membrane. Any bare spots found during an inspection need to be repaired before inclement weather arrives. The area should be cleaned, and an application of fibered emulsion or solvent-based roof coating should be brushed or squeegeed on the area.

Because these repairs are typically carried out in cold-weather conditions, the coating should be stored in a dry place, ideally with temperatures between 60 degrees F and 80 degrees F.

Solvent-based products are combustible and should be kept away from open flames. Emulsions must be kept above freezing, both in the can and as they cure on the roof, to prevent the deterioration of the product.

Because of their sensitivity to cold, emulsions typically are applied at temperatures of 40 degrees F or higher. The coatings manufacturer should be contacted for specific product, coverage and temperature recommendations.

Polymer-modified emulsion and solvent-based coatings typically have better cold-temperature properties and could be considered for all of the above applications.

The viscosity of bitumen is temperature-sensitive-thinner and more fluid when hot, thicker and more viscous when cold. Cold-applied asphalt roof coatings are formulated to be usable at ambient temperatures from 40 degrees F to 120 degrees F. Water-based coatings and coal-tar coatings usually are applied at 50 degrees F or higher.

Here are important tips to ensure a successful system application:

-Storage. Keep the product as close to room temperature as possible. A heated warehouse is ideal, but if it must be kept outside, store the containers close together under a tarp. This will slow down the internal temperature drop of the product, keeping the viscosity and application properties closer to standard for a longer period of time. This also is important when using asphalt-saturated roofing felts in cold weather. These felts can become brittle when cold and can crack at temperatures less than 40 degrees F. Unsaturated membranes, such as polyester, are not affected by cold temperatures, but must be kept dry.

-Heating. With proper storage, heating should not be necessary. On the job site, heated storage cabinets/units for heavier-bodied coatings, or warming devices that use circulating oil to heat liquid roofing materials for easier spray application, may be used.

-Surface preparation. Never apply the product to a frost- or ice-covered surface. In addition to removing frost, ice and/or snow, the surface must be dry for solvent-based coating products unless using specially formulated wet-surface products. Slightly damp conditions may be acceptable for emulsions.

-Application. If possible, wait until afternoon on a sunny day. This will enable the roof to warm up as much as possible. When working with a black roof, the surface will absorb heat, making the roof temperature warmer than the air temperature. This will accelerate the overall cure rate.

-Cure time. While modern technology permits the application at low temperature, the cure time can be longer than on a warm summer day. A product that may cure overnight at a temperature of 70 to 75 degrees F may take several days to cure at 40 degrees F. Remember that emulsion-type coatings require temperature conditions that permit thorough evaporation of the water content before the film is subjected to rainfall, freezing or standing water. Consider using a polymer-modified emulsion for use in cooler temperatures, as these products tend to have shorter set and cure times.

White elastomeric coatings have become an ever-increasing factor in roof maintenance due to their long-term durability, high reflectance values, low VOC content, ease of application and simple cleanup, as well as their rubber-like qualities.

White coatings are particularly resistant to the deteriorating effects of UV rays. The emulsion-type vehicles used in white waterborne coatings normally are based on some form of acrylic technology. Along with titanium dioxide pigment, this technology provides the backbone of resistance of UV degradation.

Applying a white elastomeric coating greatly increases the surface's reflective value, a means of reducing air-conditioning costs. White-coated surfaces can reflect up to 90 percent of infrared in the near visible wavelengths. During summer months, this can represent a significant amount of savings.

Another benefit of high reflective values is the reduction in the daily range of expansion and contraction of the roof membrane. By reflecting infrared light, heat buildup is minimized, which reduces the stresses and strains caused by the expansion/contraction cycle.

White coatings based on emulsion technology have excellent application properties by a variety of means, including brush, roller and airless spray. When using any of these techniques, care must be taken to ensure that sufficient coating is applied.

A key consideration in applying white elastomeric coating is quality of surface preparation because of possible sensitivity to problem surfaces. The roof membrane must be checked for any problems that might have developed during its exposure history. It is much easier and less expensive to detect and fix problems while preparing the surface than after the coating has been applied. Water-soluble residues, oil and grease, dirt and other foreign matter, or a heavy chalk condition, require preparatory measures like power washing, scrubbing or priming.

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