06/10/2009

Roofing: Mastics, Coatings, Adhesives

By Richard L. Fricklas

 

Sustainability of roofing systems requires that the systems be repairable. Any roof system can be punctured if the impact is great enough. Repair materials need to be compatible with the roof system in place; that, in turn, requires the building manager to know what’s overhead.

Commercial (low-slope) roof systems can be classified as:

  • Bituminous built-up, using asphalt or coal tar pitch.
  • Bituminous polymer-modified systems.
  • Sprayed-in-place polyurethane foam with coating.
  • Single-ply non-bituminous.
    • Weldable thermoplastics.
    • Non-weldable elastomeric.
  • Metal roof systems.

Proper repair requires that you know what roof system is in place so that you use the appropriate materials.

BITUMINOUS BUILT-UP ROOFING SYSTEMS
The traditional built-up roof consists of multiple layers of bitumen-saturated roofing felts glued to one another with bitumen, with a “flood-coat” of more bitumen into which roofing aggregate has been embedded. Although less common, some built-up roof systems are surfaced with mineral cap sheets or just with paint-type coatings.

Asphalt
Asphalt is derived from petroleum as a heavy residual material (bottom of the barrel) (see Fig. 1). Note that “mineral spirits” is part of the same distillation process. Asphalt is completely compatible and soluble in this “paint thinner.”

When possible, repairs should be made with compatible materials. Asphalt mastic, found on every roofer’s truck, in lumberyards, and at roofing supply yards, is readily available. The ingredients will include petroleum asphalt, mineral spirits, fibers, and fillers. The flash point (the point at which the compound would ignite in the presence of a flame) is generally above 100 degrees F. (38 degrees C.), so the product isn’t designated “red label” or flammable.

For residential use, the mastic is packaged in 1-gallon pails. For commercial use, generally, more than 1 gallon is needed to effect repairs. In many cases, commercial roof mastic is provided in 2.5-gallon pails. Five-gallon pails are available everywhere; however, that’s a rather inconvenient size for a maintenance person to lug around a roof.

Thick or Thin?
Depending upon the proportion of ingredients, these “cut-back” products can be as thin as water (e.g. primer) or heavy enough that, even with a trowel, the products are stiff and require a strong arm to apply. (See Table 1 for a list of products.)

After the patch is made, some loose aggregate from the surrounding area can be sprinkled into the topcoat of fresh mastic. Leaving the aggregate off has the advantage of keeping an eye on the repair to ascertain that it has succeeded, and to help you avoid stepping on a fresh patch.

Figure 2 lists common bituminous cutbacks and coatings.


Fig. 2: BITUMINOUS PRIMERS, COATINGS, MASTICS

Bitumens:

  • Asphalt
    • ASTM D312, Types I to IV
  • Coal Tar Pitch
    • ASTM D450 Type I

Solvent:

  • Mineral Spirits (Petroleum Distillate), ASTM D235
    • Boiling Range 300-400°F
    • Flash Point 100°F minimum

Asphalt Primer:

  • Solution of mainly solvent with some asphalt ASTM D-41
  • Also Coal-tar based primer ASTM D-43

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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

 


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.


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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