he North American roofing industry is witnessing increasing popu-

larity of numerous technologies aligned with the sustainability move-

ment. Among these, roof coatings are receiving significant publicity from

different groups capable of influencing consumer sentiment, including

government policymakers, conservationists and coatings manufacturers.

For example, sustainability advocates identify reflective roof coat-

ings’ use as a cost-effective way to reduce building energy consumption

in hot climates and control the heat island effect.

Roofing professionals long have recognized the viability and advan-

tages of roof coatings for surfacing bituminous weatherproof roof

membranes used as part of low-slope roof systems and possess a great

deal of experience with coating applications over roof membranes. This

is not the case with field coating steep-slope roof coverings. The fact is

the most widely used steep-slope roof covering—asphalt shingles—is

not designed to accept or require field-applied surfacings.

Coating products and paints advertised as suitable for application to

asphalt shingle roof systems currently are available and marketed pri-

marily to do-it-yourself homeowners. Promotional materials for most

of the products position field coating as a cost-effective way to extend

asphalt shingle roof system life. Language suggesting leak repair and

energy-cost savings resulting from the use of reflective coatings also

commonly is used.

Homeowners may consider field coating asphalt shingle roof sys-

tems more appealing than reroofing and seek information from roofing

professionals. The following information is intended to assist roofing

professionals who may be in a position to answer consumer questions

related to field application of coatings over asphalt shingle roof systems.

The risks and

unverified benefits

of field coating

asphalt shinglesby Maciek Rupar

37

T

Advertised benefits

Marketers of coatings for application overasphalt shingles claim their products offera range of benefits though specific claimsvary depending on the product. To learnabout products’ advertised benefits and evidence used to validate those benefits, Icollected information from 10 Web sitespromoting coating products for applica-tion over asphalt shingles. The most common claim states field-

applied coatings extend asphalt shingles’service lives. Other advertised advantagesdiffer depending on product and rangefrom simply “improves a roof ’s appear-ance” or “ultraviolet-resistant” to morespecific claims, such as “rejuvenates shin-gles” or “fixes granules in place,” to moreradical claims, such as “repairs leaks,”“forms a waterproofing membrane” or “reduces energy costs.”Arguments used to support the market-

ing claims are based on before and afterphotographs of roof systems, consumertestimonials and additional reassuring lan-guage published on coating suppliers’ Websites. Searches for test or laboratory evalu-ations of natural or accelerated weatheringstudies turned up no independently pre-pared test or laboratory reports that couldvalidate many of the claims made in theonline marketing materials.

Coating composition

A majority of coatings advertised for useon asphalt shingle roof systems share a

common binder system. Information Icollected from supplier Web sites indicatesmost of the coatings use a water-dispersedacrylic polymer binder commonly calledlatex or acrylic emulsion. Many acrylic binder systems have

proven performance in low-slope roofcoating applications. Various acrylicbinders are used in a range of successfulelastomeric roof coatings, which displayvarious degrees of elasticity, hardness,durability and permeability. Regrettably,physical property information is not con-sistently provided for the acrylic coatings I investigated. Notably, the promotionallanguage in almost all cases claims prod-ucts are vapor-permeable. Acrylic-based products are available in

a range of colors. Many suppliers promisetheir coatings perform as weather- andmold-resistant protective layers. Whitecoatings typically are advertised as reflec-tive. In some cases, it is implied coatingshelp realize energy savings by reducing theamount of heat absorbed by roof surfaces. A few acrylic-based products are said to

add thermal insulating value to roof sur-faces. Marketing materials for these prod-ucts claim their formulas contain techno-logically advanced components describedas “ceramic microspheres” or “nanotech-nology materials” characterized by ex-tremely low thermal conductivities. Some suppliers offer primers marketed

for asphalt shingle surfaces for use withacrylic water-based coatings. These primersare composed primarily of petroleum

distillates or contain acrylic resins and hydrocarbon solvents. I found few examples of nonacrylic-

based coatings marketed for applicationover asphalt shingles. Those I did findcontain SEBS or similar thermoplasticrubber binders and hydrocarbon solvents. Cured coatings are characterized as

sealants for joints between dissimilar mate-rials or as waterproofing membranes for sur-faces depending on application type. Theyare said to be clear in color, have rubber-like flexibility and accept paint finish.Products using this formulation appear to function as effective vapor retarderswhen applied as continuous film accord-ing to application instructions.

Application

Because coatings for field application overasphalt shingles are marketed primarily tohomeowners, ease of use is emphasized.Application instructions are designed forthe average home-improvement enthusi-ast. Application by paint roller and brushcommonly is recommended. Some prod-ucts, typically primers, are intended forapplication with airless spray equipment. Typical application instructions require

shingles to be clean and dry before appli-cation begins though language for thermo-plastic rubber-based coatings claims surfacedampness will not interfere with adhesion.Dirt, debris and biological growth are tobe removed. One of two options for clean-ing typically is recommended: washingwith water and detergent and then rinsingor pressure washing. A diluted bleach so-lution or proprietary cleaning agent maybe recommended for eliminating algae,lichens and mildew.NRCA and the Asphalt Roofing Manu-

facturers Association (ARMA) do not rec-ommend pressure washing asphalt shingleroof systems because doing so may dam-age shingles.Weather conditions appropriate for

coating application typically are described

38 April 2010 www.professionalroofing.net

as temperatures greater than 50 F and noprecipitation for a period necessary toachieve moisture-resistant cure levels. Rec-ommendations for coatings using hydro-carbon solvents generally are less restric-tive. The initial cure time varies depend-ing on product and/or number of coatsand ranges from 12 to 72 hours. Theupper temperature limit for applicationalso varies depending on product or maynot be provided. One supplier recommendsapplication temperatures no higher than95 F. Asphalt shingles typically are subject to

service conditions that make it impracticalto fully abide by some of the recommen-dations described. The language used inthe application instructions is consistentwith the fact that water-borne acrylic coat-ings typically are sensitive to moisture andtemperature until they cure.

Evaluation tools

ASTM D6083, “Standard Specificationfor Liquid Applied Acrylic Coating Usedin Roofing,” is the standard material speci-fication for water-dispersed acrylic coat-ings used as field-applied surfacing inroofing applications. No ASTM Interna-tional standard material specifications are available for sealants or field-appliedroof coatings using thermoplastic rubberbinders.Two standard test methods for measur-

ing roof coatings’ solar reflectance areavailable. ASTM C1549, “Standard TestMethod for Determination of Solar Re-flectance Near Ambient Temperature Usinga Portable Solar Reflectometer,” provides aprocedure for using a portable measuringdevice with an integral light source suit-able for laboratory and field readings fromsmall-area samples. ASTM E1918, “Stan-dard Test Method for Measuring Solar Re-flectance of Horizontal and Low-SlopedSurfaces in the Field,” is intended for useon low-slope roof surfaces, samples a largearea for measurement, can be used for

readings from roughly textured surfacesand requires clear midday weather to per-form measurements.Roof coatings’ thermal emittance may

be measured according to ASTM E408,“Standard Test Methods for Total NormalEmittance of Surfaces Using Inspection-Meter Techniques,” or ASTM C1371,“Standard Test Method for Determinationof Emittance of Materials Near Room Tem-perature Using Portable Emissometers.”Thermal insulating properties are not

associated with roof coatings; therefore, nostandard test methods for evaluating ther-mal insulating performance of coatings in roofing applications are available. Con-sequently, it may not be practical to vali-date statements made about thermal insu-lating performance of field-applied roofcoatings. It may be difficult or impractical to ob-

jectively evaluate the physical propertiesand performance characteristics of coat-ings marketed for application over asphaltshingles. Compliance with ASTM D6083was not indicated for any of the investi-gated products. Documentation for someof the products references standard testmethods and standard material specifica-tions; however, they are not standards usedin roofing applications. Overall, the levelof technical information presented is belowpar compared with that available for estab-lished low-slope roof system coatings.Physical property information typically

available includes density, solids content,

volatile organic compound content, wetand dry film thickness, coverage rate, application temperature range and curetime. Some suppliers publish test valuesfor additional cured film properties; how-ever, test method designations are not always provided.

Concerns abound

The roofing industry is aware of a numberof issues that could have negative conse-quences for field application of coatingsover asphalt shingle roof systems. Anyoneconsidering this type of application shouldbe aware of the concerns so they can weighthem against the benefits claimed in coat-ing product promotional materials.

Manufacturer recommendations

There are two sources available to thoseinterested in learning asphalt shingle man-ufacturers’ recommendations.ARMA Technical Bulletin No. 227,

“Field Coating of Installed Asphalt Shin-gles,” strongly advises caution when con-sidering field applying any coating overinstalled asphalt shingles. The bulletin dis-cusses problems reported after field coatingasphalt shingles and advises homeowners tocontact shingle manufacturers for approvalbefore field coating asphalt shingles. To ac-cess the bulletin, visit ARMA’s Web site atwww.asphaltroofing.org, click on All AboutRoofing, scroll to Publications and clickon Technical Bulletins. GAF-Elk Contractor Services published

ProfessionalRoofing April 2010 39

Steep Slope Technical Point No. 151-09,“Field Coating of Installed GAF-Elk As-phalt Roofing Shingles,” which does notrecommend field application of coatingsover asphalt shingles. The document ad-dresses several questions likely to be askedby roofing consumers interested in fieldcoating asphalt shingles. It is available fromGAF-Elk’s Web site at www.gaf.com/Document-Library/DocList.aspx.The ARMA and GAF-Elk documents

caution that the claims made about bene-fits of field coating asphalt shingles havenot been well-documented or evaluated.Other asphalt shingle manufacturers ei-

ther take ARMA’s position, do not publishrecommendations addressing field coatingor take the position that field coating hasnegligible effects on asphalt shingles pro-vided water-based latex paints are used.Hydrocarbon solvent-based coatings arenot recommended for use on asphalt shin-gles because the solvent may soften the asphalt coating.

Warranties

Language in two manufacturers’ shinglewarranties specifically excludes coveragefor damage to their products caused bycoating or painting. It is reasonable to ex-pect other manufacturers that do not in-clude field coating-specific language intheir product warranties would claim theexclusion applies to their products basedon their warranties’ more generally de-fined exclusions.

Drainage and permeance

Field coating asphalt shingles is at oddswith one of the fundamental working prin-ciples of shingled roofing. Shingled roof coverings shed water. In

other words, shingles rely on gravity to do most of the work of keeping out water.Sometimes, water travels underneath shin-gles via capillary action, wind force orwhen large volumes drain down valleys.When this occurs, shingles allow water

to run down and to the outside surface of a roof. When a coating is applied over roof

coverings installed shingle-fashion, espe-cially when it is intended to seal shinglesat edges or form a continuous membrane,drainage paths for water trapped under the roof ’s outer surface may be cut off. Although wind-driven rain or water entrybecause of capillary action may be con-trolled or eliminated, the most commonwater entry locations where dissimilar ma-terials meet at flashing elements can remainproblematic. The potential for damage tounderlayment and deck sheathing, as wellas leaks from water infiltrating at flashinglocations, is increased.Additionally, depending on the coating

type, field application over asphalt shin-gles may lower an asphalt shingle roof system’s vapor permeability. Asphalt shingle roof systems are vapor-

permeable because joints between individ-ual shingles allow vapor to pass through.Some coating formulations are effectivevapor retarders. Applying a vapor-retardantcoating to an asphalt shingle roof system’ssurface likely will compromise a roof as-sembly’s self-drying characteristics. Some roof assemblies may accommo-

date this with existing or additional venti-lation. For other roof assemblies, the changein moisture transport resulting from coat-ings may be too much to maintain a non-condensing environment in attic or ven-tilation spaces.

Code restrictions

Local building codes may prohibit fieldapplying coatings over asphalt shingle roofsystems. For example, 2007 Florida Building

Code: Residential, Chapter 44—High-Velocity Hurricane Zones contains the fol-lowing language applicable to reroofingresidential buildings no more than threestories in height in Broward and Miami-Dade counties: “R4402.10.18.1 Nosprayed polyurethane foam (PUF) and/or

elastomeric coating systems shall be ap-plied over existing composition shingles.”Also, 2007 Florida Building Code:

Building, Chapter 15—Roof Assembliesand Rooftop Structures contains the fol-lowing similar language: “1521.18.1 NoPUF and/or elastomeric coating systemsshall be applied over existing compositionshingles.”

Fire-resistance ratings

A field-coated asphalt shingle roof sys-tem likely does not have an external fire-resistance rating. A coating is given a fire-resistance rating as a component of a specificroof assembly based on testing at a specificroof slope. Coatings marketed for applica-tion on asphalt shingle roof systems oftendo not possess fire-resistance ratings. Roof coatings rated for fire resistance as

part of low-slope bituminous roof systemsare not suitable for application over as-phalt shingle roof systems. Fire-resistanceratings for roof coatings and roof coatingsystems designed for application directlyover bituminous membrane roof systemsare limited to roof slopes less than the 2-in-12 (9-degree) minimum prescribed bybuilding codes for asphalt shingle systemapplications. Additionally, some coatingsmanufacturers state their products are notappropriate for application over asphaltshingles.

Summing it up

No evidence currently is available to corre-late marketing claims with actual perform-ance of field-applied coatings over asphaltshingle roof systems, and such an applica-tion subjects a roof system and its ownerto specific risks the owner should under-stand before making a decision to fieldcoat an asphalt shingle roof system. A thor-ough cost-benefit analysis may prove thatknown concerns within the roofing industryoutweigh the potential benefits.

Maciek Rupar is an NRCA director of technicalservices.

40 April 2010 www.professionalroofing.net