06/03/2013

Why Asphalt? Why Now?

How a tried and true roofing system remains a top contender

By Richard L. Fricklas

 
  • /Portals/1/images/OnlineImages/2013/0613/1-spray_web.jpg

    The basic aggregate surfacing for asphalt roofs has evolved to include smooth-surfaced systems such as this one. A field-applied coating completes the process.

  • /Portals/1/images/OnlineImages/2013/0613/2-kettle_web.jpg

    Opting for asphalt roofing? You can have it delivered in a carton and melt it at the job site or order it as a hot melt liquid shipped in a tank truck.

  • /Portals/1/images/OnlineImages/2013/0613/3-cold_web.jpg

    Mastics for flashing or cold-applied membranes are created by combining asphalt with mineral spirits.

With the growth of single ply, sprayed-in-place polyurethane foam, metal, and modified bituminous systems for low slope commercial roofing, why should we be interested in asphalt at all?

How Asphalt Works
Asphalt is a dark-brown to black cementitious material created from bitumens that occur in nature or from petroleum processing. It’s used in roofing, waterproofing, and paving as both a waterproofer and a construction adhesive.

Multiple-ply hot built-up roofing (BUR) has been around for more than a century.  A typical construction used a factory-coated base sheet that was mechanically fastened to the substrate, followed by two or three ply sheets that were embedded in hot asphalt and a flood coat of hot bitumen into which aggregate surfacing was embedded. The ply sheets could be asphalt-saturated organic felt, asbestos felt, or more recently, glass fiber mats.

Because of the aggregate surfacing, these roof systems generally qualified for Class A fire resistance. Variations of these basic systems include factory-applied mineral surfacing (cap sheets) and smooth-surfaced systems that received a field-applied coating as a final step.

Asphalt serves as a hot-melt adhesive, gluing the ply sheets to the substrate as well as to each other. It can be melted in a kettle at the job site or delivered as a hot melt liquid by tank truck.

Since most asphalt starts out as a byproduct of petroleum processing, it is fully compatible with mineral spirits (which are also a byproduct of petroleum) to make cold mastics for flashing or cold-applied membrane systems. Asphalt can also be emulsified as a water dispersion for surfacing BUR systems. 

Where Can I Use Asphalt?
Asphalt is used in all our modified bituminous (MB) roof systems as a waterproofing coating for the reinforcements and also serves as the adhesive to bond the systems to the substrate. MB systems can use field-applied hot asphalt or utilize a torch to soften and fuse the sheets together. The modifiers can be classified as plastic-modified (atactic polypropylene) or elastomer-modified (sequenced butadiene-styrene or SBS).

More recently, many single-ply systems now offer fleece-backed products that can be embedded in hot asphalt, such as in re-cover applications over old BUR. Even tile roofs frequently use bituminous cap sheets or multiple layers of BUR as an underlay for the tile.

Asphalt should be applied when it is heated to a recommended application temperature. For asphalt, these temperatures apply:

For mop application: the temperature at which the asphalt’s apparent viscosity (equiviscous temperature, or EVT) is 125 cP, plus or minus 25 degrees F.

For mechanical spreader: the temperature at which the asphalt’s apparent viscosity is 75 cP, plus or minus 25 degrees F.


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Visit our website today to learn about the design flexibility of a Morton building and the endless possibilities of partnering with our designBUILD team.


Wood construction is both cost and energy efficient. Check out Morton Buildings and our designBUILD team online today to discover all the benefits of post-frame construction.


When choosing a metal-clad building for your next construction project, consider Morton Buildings, Inc., and their designBUILD team, we’ll make your dream a reality.

We Can Help You Reduce Energy by 30%

Our mission is to help our customers manage their buildings' energy costs, improve reliability, and enhance performance while having a positive impact on the environment.
CLICK HERE to find out how.

 

Add highly responsive multi-zone comfort to any building project, in any climate. Our CITY MULTI H2i R2- and Y-Series VRF systems give you flexibility to fit the needs of any building. Enjoy 100% heating capacity at 0°F outdoor ambient, and 85% heating capacity at -13°F outdoor ambient.  For more information, log on to www.mitsubishipro.com


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Tennant Company is a recognized leader in designing, manufacturing and marketing solutions that help create a cleaner, safer, healthier world. With thousands of satisfied customers already using award winning ec-H2O technology, why not see what you're missing? Test ec-H2O on your soils in your facility. Get a free demo.

 

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