Polyurea Roofing System over Double Coverage Roll Roofing and Concrete Deck

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This Video is of a Polyurea Roofing System over Cap Sheet System.

 

Roof Coating
Polyurea coatings make an excellent protective covering for polyurethane foam roofs. Polyurea can be formulated to meet specific performance requirements due the wide range of physical properties that can be formulated. Some systems have the "Cool Roof" ENERGY STAR® rating for color and reflectivity. These reflective coatings can help reduce the amount energy consumption buildings use for heating and cooling. The fast cure time and insensitivity to moisture allows for a quicker installation with a wider application window. Proper surface preparation and substrate condition is always necessary.

 

POLYUREA COATINGS FOR REHABILITATION OF METAL ROOFING

L. D. Stephenson, David Bailey, Ashok Kumar, and Vincent Hock

U. S. Army Corps of Engineers

Engineer Research and Development Center

Construction Engineering Research Laboratory

P.O. Box 9005

Champaign, IL 61826-9005

ABSTRACT

High-build multi-component polyurea-hybrid spray-on coatings can provide the capability to quickly and cost-effectively rehabilitate metal roofs in lieu of more costly and disruptive roof replacement. The multi-component coating can be sprayed onto a deteriorated coated metal roof surface, with mini-mal surface preparation.

An aluminum alloy roof on a barracks building at Wheeler Army Airfield, HI was chosen for coating application. The barracks were occupied during the rehabilitation process, necessitating careful plan-ning and monitoring of changes in the weather, especially the wind and rain. The topcoat, a copper polyurea-hybrid roof elastomer, was applied using a two-component proportioner system and a spray gun with a No.2 spray tip at 1,200 psi back pressure. The setup time of the coating material was sev-eral seconds; it was dry to touch in 45 seconds, and easily handled within several minutes, with a final thickness of the coating system of 40 mils.

The polyurea-hybrid coating proved to be economical to apply, and can be expected to extend the ser-vice life of the metal roof by providing a very tough moisture impermeable spray-on membrane, which effectively seals surface defects, even around penetrations, pinholes and seams.

KEYWORDS:

polyurea polymer, roof rehabilitation, roof restoration coatings, multi component spray polymer, moisture proof roof membrane, metal roof rehabilitation
 

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INTRODUCTION

Problem

Wheeler Army Airfield, near Honolulu, HI has identified severe corrosion problems on metal roofs at their installation due to exposure in a microclimate of alternate rain and sunlight. Among these structures are hangars which protect mission essential aircraft, spare parts and maintenance equipment, as well as barracks, which house the mission essential personnel. Several buildings were identified at Wheeler Army Airfield whose metal roofs had degraded due to exposure to the hot and humid envi-ronment of Hawaii, and had received Roofing Condition Index ratings of 20-50 (on a scale of 100 be-ing "new" condition). Examples of these degraded roofs are shown in Figure 1. In addition, the fac-tory coated standing seam metal roof panels can degrade by high ultraviolet light (UV) exposure. It is estimated that about 80 additional Army Installations have standing seam metal roofs that suffer these same problems, as do many Tri-services Installations. Severe corrosion of metal roofs occurs due to the year-round wet climate and accumulation of contamination on the surfaces, which further degrades the metal.

For mission-specific-buildings, CONUS installations have approximately 77 percent of the Army’s total roofing found on these types of facilities. Of these 340 million square feet of roofing, metal roofing accounts for 21 percent.

1 Over the past decade, problems with corrosion of metal roofs and degradation of metal roof coating have been addressed by researchers at the U. S. Army Engineer Research & Development Center (ERDC), Construction Engineering Research Laboratory (CERL).

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A recent Cost of Corrosion Study for DoD Facilities and Infrastructure

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concluded that the DoD spends $1.77 billion annually on maintenance due to corrosion. Those annual corrosion mainte-nance costs that can be attributed to "General Building Maintenance," which includes roofing, are $627M. In addition, roofing degradation was listed in multiple categories (e.g., Enlisted Unaccompa-nied Personnel Housing, General Administrative Building, and Family Housing Dwelling) in the top 25 highest contributors to the cost of corrosion.

Advanced roofing rehabilitation technology is required to economically solve metal roofing corrosion problems and extend the service life of these existing deteriorated roofs, which in the long term, will protect aircraft, mission-support equipment, and electrical-mechanical equipment housed within from environmental corrosion, and help to maintain better living and working conditions inside buildings.

 

 

Objective of This Project

The objective of this project was to evaluate an innovative roofing restoration technique, which utilizes a sprayable multi (plural) component polyurea hybrid polymer coating applied over an existing deteriorated metal roof coating. The ease of use, cost effectiveness and functionality of this innovative

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coating technology in a severely corrosive atmosphere was evaluated.

Polyurea-Hybrid Roof Elastomer Coatings

A polyurea-hybrid roof elastomer coating was identified as having the capability, when applied over an existing deteriorated roof, to economically provide a moisture proof membrane that would sig-nificantly extend the service life of the deteriorated roof, a minimum of 15 years. There are a number of commercially available sprayable membrane-producing coatings from the polyurea families of coat-ings that have the potential as roof rehabilitation coatings. The coating chosen for this rehabilitation is a multi-component polyurea hybrid. All polyurea coatings are composed of a two-component A-side (Polyisocyanate Pre-polymer) and B-side (Resin Blend Formulation).

The materials selected for use on this project were VFI™-11 primer and the VFI™-535 poly-urea-hybrid topcoat, manufactured by VOLATILEFREEINC™ (VFI™), Brookfield, WI. The topcoat material contains a copper pigment that gives the appearance of a metallic coating when properly ap-plied. The plural component polyurea hybrid coating material applied in this project had 98% solids, and met the ASTM criteria for tensile strength, elongation, and permanent set (ASTM D-412)

7, as well as hardness (ASTM D-2240)8, tear resistance (ASTM D-624)9, and water vapor permeability (ASTM E-96, method BW)10

, as shown in Table 1.

 

PROCEDURE

A fully occupied barracks was identified as having a 20,000 square foot aluminum alloy roof that was in need of replacement, as shown in Figure 2. Due to surface degradation and leaks this roof was scheduled for complete replacement. After this building was identified, the logistics of coating this fully occupied barracks with vehicles surrounding it, was analyzed to determine the many contin-gencies that would have to be addressed during the coating process. Some of the items that were ad-dressed prior to start of work were the limited staging area, the close proximity of an operating child care center, the many vehicles that could be effected if overspray occurred, the need to isolate the fumes so that they did not enter the air handling system of the barracks, the effect of weather on the application process and the necessity of the pigment of the coating to match the copper color require-ment for this installation’s building.

The on-site coating manufacturer technical representative, who was trained by the coating manufacturer on surface inspection and preparation required for his product’s successful application, conducted a visual inspection of the roof surface before the work started. The roof was then pressure washed to remove any mildew and chalking from the existing roofing surfaces. Where mildew or other fungus growths were noted, a mixture of 80% water, 15% bleach, and 5% of a commercially available mildewcide, was applied to remove any mildew or fungus growths.

The roof was again visually inspected for any defects such as holes, missing caulking or seal-ant, missing fasteners, etc. Defects such as missing fasteners that were found were repaired. Open

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joints in roof seams and vents, or other openings larger than 1/8", were sealed with polyurethane seal-ant (Sikaflex-1a, Dark Bronze), one-component construction sealant.

Over a three day period, the entire roof was primed with a two-component water based epoxy primer using a conventional airless spray system. The topcoat, a copper polyurea-hybrid roof elas-tomer, was applied using a Gusmer H20/35 two-component proportioner system shown in Figure 3 and a Probler spray gun, shown in Figure 4. The polyurea-family of coatings normally requires a heated fluid line for both components A and B to reduce the viscosity for spraying. The plural component proportioner system has fluid hoses with in-line heating elements. Normally, the spray gun filter screen is used to ensure small particles of material do not flow through the lines. However, when spraying the copper pigmented coatings, the filter was removed, as copper pigment powder would plug the in-line spray gun filter screen.

Setup time before spraying included ½ hr of preheating on each side using in-line 7000W heat-ing elements wrapped around the fluid hoses. A 200 foot length of heated hose was used on this pro-ject. The spray equipment was originally set to have a 2000 psi initial back pressure at gun tip, which was later reduced to 1500 psi, then finally to 1200 psi to reduce overspray. Higher spraying pressure and higher material temperature would have produced more overspray. The original spray gun fluid tip selected was a No. 1 tip that produced a round pattern, not oval as expected. The tip was later changed to a No. 2 tip, which produced the desired oval pattern.

The polyurea-hybrid coating line heat was set and maintained at 150

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F. The polyurea-hybrid component A and B were fed through separate heated lines to the spray gun where the A and B materi-als were combined at the spray tip. As the components of the polurea hybrid exit the spray gun, they are combined and immediately begin to crosslink. The setup time of the material was several seconds, dry to touch in 45 seconds, and easily handled within several minutes after the material cooled. It should be noted that polyurea coatings can be formulated for shorter and longer setup times. Short setup and cure times are generally necessary to prevent runs and sags in the coating that would nor-mally be experienced when spraying high-build coatings; using high volume spray equipment; on a sloped roof. The short setup time also facilitates coating applications where inclement weather may be a factor. Because of the heated lines and fast setup times, the polyurea materials can be effectively sprayed in cold weather where conventional coatings cannot.

Application of the polyurea was required to be 6-inches up from the base of the ventilation stacks and vents to ensure the sprayed membrane would not allow water to wick in around the base of the stack or vent. However, when coating operations began, the distinct color variance between the original beige color of the barracks roof and the newly applied polyurea-hybrid copper color was very apparent. Therefore, the entire outer surfaces of the ventilation stacks and vents were coated with the polyurea-hybrid system. Figure 5 shows the polyurea coating primer in the initial stages of applica-tions.

 

 

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To satisfy the project coating thickness documentation requirement, a National Association of Corrosion Engineers (NACE) certified coating inspector measured coating thicknesses after the appli-cation. The thickness was estimated after the fact, based on observations of the application, test panel coatings measurements, computing the theoretical coverage based on the amount of polyurea sprayed on the roof areas, and the approved 15-year coating manufacturer’s and applicator’s warranty.

During the spraying operations, any noted seam tape lifting was repaired using the polyurea quick setup actions to act as an adhesive to re-adhere the seam tape to the surface then applied the polyurea material on top of the seam tape effectively sealing the area.

RESULTS AND DISCUSSION

The plural component polyurea hybrid coating application was accomplished in March 2008 in less than 1 month. This polyurea hybrid was applied to the existing aluminum alloy roof with its exist-ing coating left intact, but power washed clean with minor repairs performed on the roof. The test ma-terial’s typical coverage was estimated at 4000 sq ft of coverage per 100 gallon drum set (50 gallons of material in each drum). This roof had been scheduled for complete replacement. As a result of this re-habilitation, the roof is now expected to have at least an additional 15 years service life

There were several lessons learned during this project that could help in future applications of this polyurea coating. These are provided and have been broken down into the categories of site-related and coating installation related.

Site related lessons

The roof chosen for this as the demonstration/implementation project was on a fully occupied bar-racks, adjacent to a utilized child care facility. Considering these factors, several extra precautions had to be taken.

  1. Time on site for preparation and painting operation times had to be adjusted to accommodate the occupants during their normal duty hours.
  1. Private vehicle covers had to be purchased to cover vehicles that were left in the spray zone when the roof was being coated.
  1. Continual personnel and vehicle traffic was present during the coating application requiring extra care to prevent coating overspray. No-parking signs and traffic cones were used to help control ve-hicle access to the staging area.

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The roof chosen for this coating application was on a designated historic building, and there-fore, it was required that the newly applied coating closely match the colors of roofs on other nearby buildings. This installation site was chosen for its severely corrosive environment, and with that came several weather related lessons learned during application of the coating. Weather had to be monitored closely during application, as wind gusts and rain showers affected the quality of the coating. Moisture droplets would cause blistering so, rain had to be avoided during application. The wind gusts could cause overspray. The wind gusts combined with the slope of the roof and close vehicle parking slowed the material application process.

The quick setting of the polyurea-hybrid material did not allow for overspray to blend in to newly sprayed areas. In many cases the amount of overspray detected was attributable to the standoff distance of the spray gun to the surface, the angle of impact of the sprayed material, wind gusts, the proportioner’s back pressure, and spray tip selection. Figure 6 shows an example of the operator gen-erated overspray observed during this project. Overspray was visible as dull area "halo effects" on shiny surfaces. Figure 7 shows the typical appearance of overspray on a finished test coupon. Note that the polyurea-hybrid overspray droplets do not flash or coalesce together and cure almost immedi-ately upon contact. As was noted earlier, the overspray problems were minimized by adjusting the spraying pressures. The completed application of the polyurea coating can be seen in Figure 8. The bright copper color aged to a darker copper brown within a few months

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Other application related les-sons-learned are as follows:

  1. Polyurea-hybrid material should be applied and completed one section at a time. Normal painting practices involve the "detail work" such as inside corners and crevices, etc. being applied and completed first. The high output/high build coating of the spray system would lead to coating waste and varying coating thickness and excessive halo effect from the overspray if the detail work was accomplished separately.
  1. Both components A-side and B-side of the polyurea must be thoroughly mixed in the storage con-tainers prior to changing out drum sets to ensure complete mixing. This is particularly important if the coating is pigmented to ensure the pigments are properly suspended in the coating resin vehicle.
  1. It is important to keep both components, A-side and B-side, of the polyurea material separate from each other during mixing. Even small amounts of cross contamination of either component enter-ing the other material container can immediately start the polymerization process in the storage container. This includes mixing equipment. It is very important to use separate stirring motors for each component side or cross contamination and premature cross linking of the material will occur.

 

 

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    1. Since the set up time is almost instantaneous, the pressure in one spray hose must match the other, otherwise the material will blend inside the nozzle and clog the nozzle.
      1. The texture of the coating will vary with the thickness of the application. Lower thickness exhibits an orange peel appearance. The texture affects the color/reflectivity for at least the first two weeks. Over time, the top surface will lose its sheen and the color/texture variation will be less noticeable.
      1. "As-built" drawings indicated that the metal roof was a low carbon steel alloy, however, upon ap-plication of the coating, it was discovered that it was actually an aluminum alloy. This necessitated a change in the contractor’s thickness measuring procedure, since their ferrous metal dry film thickness gages did not provide proper thickness. The lessons-learned here are to not rely solely on "as-builts," and to specify a gauge that can measure thickness on both ferrous and nonferrous sub-strates.

SUMMARY

The multi component polyurea-hybrid coating technology demonstrated/implemented in this project can provide a quick and cost effective method to rehabilitate the exteriors of metal roofs in lieu of more costly and disruptive replacement actions. On structurally sound existing roofs that have cor-rosion and water intrusion concerns, the polyurea-hybrid coating can extend the service life of the roof by providing a moisture impermeable spray-on membrane that will effectively seal the surface defects such as pinholes, seam leaks, etc.

The setup, application and testing procedures, to verify the correct amount of coating has been applied, for the plural component polyurea hybrid coating are more difficult than that required for standard spray-on or brush-on coatings. The polyurea hybrid coating material requires special applica-tion equipment, training, is very sensitive to moisture, requires special mixing, handling and storage controls. The resulting coating is a very high build, fast cure, 90-100% solids coating that uses or emits no solvents.

REFERENCES

  • Bailey, D.M., "Army roof Management and Improvement Opportunities," CERL Special Re-port 99/62, U. S. Army Engineer Research & Development Center (ERDC), Construction En-gineering Research Laboratory (CERL), July 1999.
    1. Kumar, Ashok, L. D. Stephenson and Robert H. Heidersbach "Corrosion Control for Military Facilities" in
    1. Handbook American Society for Metals (ASM) International
      1. , Materials Park, Ohio, 13C (N/A), pp. 141 -144, ISBN No. ISBN-13; 978-0-87170-709-3, Oct-2006.
        1. Myers, J.R., Ashok Kumar and L.D. Stephenson, "Materials Selection Guide for Army Installa-

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    tions Exposed to Severely Corrosive Environments," ERDC/CERL, Champaign, IL, Report Number ERDC/CERL TR-02-5, May 2002.

    1. Murray, J.N., L.D. Stephenson and A. Kumar, "Electrochemical and Physical Evaluations of Coil Coatings on Metal Coated Steels for Roofing Applications," Volume. 47, pp 136-145,
    1. Progress in Organic Coatings
      1. , 2003.
        1. Stephenson, L.D., and Kumar, A., "Service Life Prediction of Coating Systems Used in Metal Roofing," in
    1. Proceedings, National Association of Corrosion Engineers (NACE) International
      1. , Denver, CO, April 2002.
        1. LMI Draft Report to the DoD: "The Annual Cost of Corrosion for the Department of Defense Facilities and Infrastructure," May 2007.
        1. ASTM D412-06a
    1. Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastom-ers-Tension,
      1. American Society for Testing Materials (ASTM) International, West Consho-hocken, PA, 15 Dec 2006.
        1. ASTM D 2240-05
    1. Standard Test Method for Rubber Property- Durometer Hardness
      1. , American Society for Testing Materials (ASTM) International, West Conshohocken, PA, 15 Aug 2005.

        9. ASTM D624

    Standard Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers,

    American Society for Testing Materials (ASTM) International, West Conshohocken, PA, 01 Nov 2007.

    10. ASTM E96/E96M-05

     

     

    Standard Test Methods for Water Vapor Transmission of Materials

    , American Society for Testing Materials (ASTM) International, West Conshohocken, PA, 01 May 2005

     

    ACKNOWLEDGEMENTS

    The authors wish to recognize the Sponsors of the DoD Corrosion Prevention and Control Program: (1) Office of Under Secretary of Defense, Office of Corrosion Policy and Oversight (Director, Mr. Dan Dunmire); (2) Deputy Assistant Secretary of the Army Acquisition Policy and Logistics (Army Corro-sion Control Prevention Executive, Mr. Wimpy D. Pybus); (3) Assistant Chief of Staff for Installation Management (Mr. David Purcell); (4) Headquarters, U.S. Army Installation Management Command (Mr. Paul Volkman).

    Ms. Katharine Sweeton-Windsor of the U.S. Army Corps of Engineers at Louisville District provided valuable assistance/expertise in selecting this material, as well as in providing guidance during its ap-plication.

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    Value

    Solids

    Tensile per ASTM D-412

     

    Elongation per ASTM D-412

     

    Permanent Set per ASTM D-412

     

    Hardness Shore A per ASTM D-2240

     

    Tear Resistance per ASTM D-624, Die C

     

    Water Vapor Permeability per ASTM E-96, method BW

     

    TABLE 1- Properties of Polurea Coatings Applied

    Property

     

     

     

    Coating related lessons

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    Polyurea Roofing System over Existing Roofing Warranty

    Polyurea can be applied over many clean existing Roofing Conditions.

    EPDM Roofing Systems

    Roll Roofing Systems

    Built-up Roofing Systems

    Over new Spray Foam Systems

    Torch Roofing Systems

    Cap Sheet Systems

    Metal Roofing Systems

     

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