Cold process systems consist of multiple plies of reinforcement sheets that are set in a cold adhesive (solvent based or water based). These systems are often referred to as cold process BUR systems because the application procedures are similar to hot applied BUR systems. The most common reinforcement felts are manufactured from fiberglass or polyester, which is either stitch bound or spun bound.
One of the primary advantages of cold process roof systems is their relative ease of application. Very little equipment is required and three or four workers can complete most applications. The systems can be completed as new or remedial construction or can be applied over existing smooth-surfaced roof systems in an effort to extend the service life of an existing roof system.
The application procedures vary based on the manufacturer of the material that is used. It is essential that the applicator comply with the material manufacturer’s latest printed specifications during the application procedure.
Proper Application Procedures
Cold applied adhesives have different physical properties than hot applied bitumen, so their application procedures differ greatly. The differences in application requirements and techniques must be examined carefully to ensure a quality installation.
Applying the adhesive at the proper application rate is the most important factor in a successful installation. If the applicator applies too much or too little adhesive material, it can cause problems. 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 decreases.
Applying the adhesive at rates above the recommended coverage slows the curing process, resulting in a membrane that may not fully adhere to the substrate. In effect, the thicker coat of liquid adhesive will cause the membrane to “float” on the uncured adhesive rather than fully adhering to the substrate. This is essentially the same effect as another common problem: 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.
It is known that 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 one-third. This will not only add substantial costs to the project, it will take much more time for the material to cure - and it might not cure properly.
To ensure that the material is applied at the proper coverage rate, the application area should be measured. Next, the amount of material that is required to cover the area should be calculated, and only that amount should be applied.
For instance, let’s say the required coverage rate is 1.5 gallons per 100 square feet and the application area is 50 by 20 feet (1,000 square feet). The amount of material required in this case is determined as follows:
Application area: 1,000 sq. ft./100 sq. ft. = 10
Coverage rate: 1.5 gallons x 10 = 15 gallons
As applicators gain experience with the use of the material, they get used to the visual appearance of the proper coverage rate. However, it is recommended that they follow this time-proven application technique. Referring back 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 is also 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. Due to this fact, it is imperative that the applicators and others avoid walking over the newly applied membrane for a significant time period. In some instances it may be a couple of days.
The detrimental effects of trafficking over a wet and uncured cold process system may be displacement of the membrane or displacement of the adhesive, leaving voids within the system. The slow cure rate of the adhesive can be advantageous in some cases, as displaced or improperly installed membrane sheets can be easily repositioned to their proper place within the system for a period of time after the initial application.
As with all roofing and waterproofing projects, it is recommended that the applicator meet with the project designer and material manufacturer prior to the application procedure. All of the system component materials and application procedures should be reviewed to ensure that all parties are familiar with the system criteria. It is important that all of the parties agree with all application procedures and detail requirements prior to system installation.
The material manufacturer’s requirements and specific project constraints warrant that these meetings occur prior to all projects. Unnecessary delays and/or confrontations during the project can be avoided through this meeting.
Cold applied adhesives can be applied using spray equipment, squeegees, brushes and trowels. The proper application procedure for the specific manufacturer’s material should be agreed upon at the outset of the project. If spray equipment is authorized for use, the applicator should train the work crew in the proper use of the equipment. It may be beneficial to have the work crew complete a test area over the existing system in the presence of the required parties. This will give all parties the opportunity to visually inspect proper coverage rates and rectify problems with the equipment.
The work crew should be properly trained in all aspects of cold adhesive system applications. Most importantly, the coverage rates for the project manufacturer’s materials should be reviewed, including application over different substrates and how to control the rates. The coverage rate recommended varies with the different manufacturers; the coverage rate also varies based on the substrate. Typically, 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. They should know whether the sheets must be cut and allowed to relax prior to the application into the adhesive, how the roll should be set in the adhesive, and if the roll must be broomed in place. The work crew must also be trained in proper seam adhesion. With multiple plies of polyester or fiberglass felts, the adhesive forms a continuous, seamless application. 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 materials, the work crews should also know how to properly store and handle the material.
During the course of the project, quality control can be conducted by monitoring the daily temperature and the coverage rates of the adhesive. It should be stressed that foot and equipment traffic be avoided at new application areas and strict housekeeping measures should be implemented. In particular, there should be no storage of material or equipment in new areas. When using modified bitumen sheets, all of the seams should be inspected for proper adhesion.