Cold-applied Roofing and Waterproofing Strategies
Cold-applied roofing and waterproofing systems have been available in the U.S. markets for more than 50 years. Briefly defined, cold-applied systems are waterproofing or roofing applications that utilize a cold adhesive (solvent-based or water-based) in the adherence or fusion of the felt. These systems were designed primarily to eliminate concerns associated with hot bitumen application by substituting asphalt cutbacks for the hot-mopped bitumen as the interply and surfacing bitumen. Although variations of these systems have been used in the United States for many years, they have never seriously contended with hot-applied built-up systems for market share. Predominately, the use of cold-applied systems has been restricted to repair and maintenance of hot-applied built-up systems.
In recent years, the market share of these systems has expanded due to increased environmental regulations of hot-applied systems, new material developments and technology, and an ascent of situations where conventional systems prove impractical. Current industry data indicates that nearly 10 percent of all BUR and modified-bitumen systems are cold applied. This growth trend is expected to continue.
This growth spurt has resulted in an increased use of these systems by contractors who were more accustomed to built-up and torch-applied applications. It also has led to increased attention from manufacturers to provide materials to meet the market demands. In some cases, both of these parties are entering uncharted territories.
Proper Application ProceduresAlthough these systems are relatively easy to install, the proper installation procedures must be completed for successful application. Some of the more common application errors include the following:
- Entrapment of moisture in the insulation or membrane
- Inadequate or excessive use of adhesives and/or coatings
- Failure to set reinforcement sheets in the adhesive properly
- Improper preparation of the substrate or insulation
- Application of materials in unsuitable weather conditions
- Some coatings have a tendency to peel in ponded water
Applying the adhesive at the proper application rate is the most important criteria of a successful installation. It also is the most common application problem, if the applicator applies too much or too little adhesive material. When the adhesive is applied at rates below the recommended coverage, the material may cure too quickly. In this case, the adhesion strength of the material is weakened and the performance of the system suffers.
Applying the adhesives at rates above the recommended coverage results in a membrane that may not fully adhere to the substrate because it substantially slows the curing process. In effect, the thicker material will cause the membrane to “float” on the uncured adhesive rather than fully adhere to the substrate. This is essentially the same effect as applying the adhesive at lower than specified temperatures. Solvent-based adhesives become thicker at lower application temperatures. It is imperative that the applicators understand that in these applications, more is not better.
Controlling the coverage rate of the adhesive produces the desired thinner, more uniform and continuous adhesive application. Controlling the material’s temperature is also critical in achieving a uniform and proper coverage. For instance, if the required coverage rate of the material is 1.5 gallons per square, and the applicator applies the adhesive at a rate of 2 gallons per square, the adhesive use is increased by 25 percent. This will not only add substantial costs to the project, it will add approximately 50 percent more time to the proper cure of the material.
To ensure that the material is applied at the proper coverage rate, measure the application area, calculate the amount of material that is required to cover the area, and then apply that amount of material. For instance, if the required coverage rate is 1.5 gallons per 100 square feet and the application area is 50 by 20 feet or 1,000 square feet, the amount of material required is 15 gallons.
Application Area: 1,000 square feet / 100 square feet = 10
Coverage Rate: 1.5 gallons x 10 = 15 gallons
Referring to the above example, the applicator should divide the area into three equal parts, place one 5-gallon pail in each area and apply the full contents of each pail into each area. The adhesive should be applied in a continuous, even application throughout each area, leaving no voided areas in the substrate. The membrane is then fully embedded into the adhesive in accordance with the material manufacturer’s latest printed requirements.
The application of the membrane also is slightly different than in hot-mopped or torched systems. The initial adhesion strength, commonly referred to as “green strength,” of the adhesive is not as strong as the initial adhesion strength of hot bitumen. It takes a significantly longer period for the volatiles to flash off from the cold adhesive than it takes for hot bitumen to cool off and set, which is almost instantaneous. Due to this fact, it is imperative that the applicator avoid walking and trafficking over the newly applied membrane for a significant time period — in some instances, it may be a couple of days. Ironically, though, the slow cure rate of the adhesive can be advantageous, as displaced or improperly installed membrane sheets can be easily re-positioned for a long period after the initial application.
The work crew should be trained properly in all aspects of cold adhesive applications. Most importantly, the coverage rates for the project manufacturers’ materials, particularly over different substrates, and how to control the rates should be reviewed. Typically, a perlite or wood-fiber insulation will require more adhesive than a smooth base sheet, polyester or fiberglass felt or polyisocyanurate insulation.
The work crew should be trained in the proper method of membrane application; whether the sheets must be cut and allowed to relax prior to the application of the adhesive; and if the roll must be broomed in place. The work crew also must be trained in proper seam adhesion. With multiple plies of polyester or fiberglass felts, the adhesive forms a continuous seamless membrane. Some modified bitumen manufacturers require heat-welding or torching to fuse the membrane seams, whereas some only require adhesive application at the seams. Due to the temperature constraints of the material, the work crews also should have knowledge in how to store and handle the material.