Understanding Roofing Systems

Part 3: TPO and PVC

TPO is a single-ply roofing material that can be manufactured in bright white; there is not an urgent need to coat a newly installed TPO roof system. However, there is a demand for coatings that will extend TPO roof systems' life cycles.

Unfortunately, TPO roof systems' smooth, inert surfaces present a significant adhesion challenge to coatings. For TPO roof systems, manufacturer-approved primers are available, allowing for an elastomeric white top coat, such as water-based acrylic. Suffice to say this is not a common application and is an area of ongoing research.

PVC also is smooth, chemically resistant, water-resistant and not easily coated—special primers are required to coat these roof systems. PVC's high levels of liquid plasticizer seem to present a bigger challenge than its slick surface. The polymer's chemical resistance also inhibits the development of suitable primers. PVC gets its white color from pigments added to the polymer during the manufacturing stage.

It's worth mentioning that TPO and PVC membranes easily can be misidentified in the field. Because they require different primers and coatings, examining a test patch is a prudent caution before coating an unidentified white membrane.

Source: Professional Roofing

Understanding Roofing Systems

Part 2: Modified Bitumen

Polymer-modified bitumen roofing is a subset of asphalt roofing. Before these roofing sheets are formed, asphalt is heavily modified with APP or SBS rubber. These two technologies provide products with significantly different properties. SBS materials can be installed in moppings of hot asphalt, with cold adhesive or torch-applied. They may be used as hybrid systems and typically are finished with a mineral-surfaced cap sheet. A thick APP base sheet often is used with granulated SBS sheet on top, and, in most parts of the U.S., it is torch-applied rather than adhered with hot asphalt or adhesives. APP most commonly is available as a smooth-surfaced material though granule surfaces also are available.

Recently, some manufacturers have introduced white polymer-modified bitumen cap sheets that may be used to cap traditional BUR systems. If they provide reflectance values above 0.70, the roof systems qualify for an exemption from California's Title 24.

Various protective and reflective coatings also can be applied to polymer-modified bitumen substrates in the field.

Much of what applies to BUR systems also applies to polymer-modified bitumen roof systems. Polymer-modified bitumen roof systems generally are compatible with coatings developed for conventional BUR systems; aluminum and white coatings commonly are used. Elastomeric acrylic coatings can be applied to smooth polymer-modified bitumen and mineral-surfaced cap sheets to turn their black surfaces white and extend roof system life cycles while lowering energy costs.

Elastomeric acrylic coatings featuring non-bleed formulas recently were introduced. These coatings provide asphaltic substrates with a cool, bright white, protective seal. These specially formulated coatings maintain their bright white surfaces for long-term performance.

Roof systems with asphaltic substrates must be aged at least 90 days before white elastomeric acrylic coatings can be applied. If a substrate previously was coated with an unknown coating, an adhesion test must be performed. After a successful adhesion test, all loose existing coatings and debris must be removed and the roof surface power washed with water. Excessively soiled or greasy surfaces—common on smooth APP—may require additional cleaning with a stiff-bristle broom or scrub brush.

Mineral-surfaced cap sheets are perhaps the easiest to coat in the field. These surfaces are rough enough to provide excellent adhesion but not so rough as to require a large volume of coating material. Mineral-surfaced cap sheets have a surface roughness of 30 to 50 mils. An initial coating of 10 mils with asphalt emulsion tends to fill in the voids and serve as a good substrate for a white coating.

A smooth polymer-modified bitumen roof system also can be coated with an asphalt emulsion coating and topped with a compatible white acrylic coating depending on the target reflectivity value.

Source: Professional Roofing

Wherever a beautiful soul has been, there is a trail of beautiful memories.

In loving memory of Naphis Mitchell-Reyes

Naphis Aliel Mitchell-Reyes, age 56, passed away on October 16, 2021, in Dallas, Texas. He was born on March 10, 1965 to parents, Louis Manuel Mitchell and Rosa Delima Reyes in Bayamon, Puerto Rico. Naphis was a man who valued honor, truth, and family above all. Always seeked excellence in all his endeavors; he would say "I will never stop learning." He was loved by every person that met him, he will forever be remembered in our hearts.

Naphis is preceded in death by his father, Luis Manuel Mitchell-Estrada. He will be lovingly remembered by his wife of 14 years, Amparo Pastor. Also to cherish is memory will be his daughters: Veronica Mitchell-Garcia; Elena Mitchell-Pastor; and Rebeca Cabanes Pastor. As well as his sons: Naphis Aliel Mitchell Jr. and Jose Cabanes Pastor. Grandchildren Aliel Mitchell, Sofia Garcia, Mateó García, and Annie Cabanes.

Understanding Roofing Systems

Part 1: BUR (Built-Up Roof)

The roofing industry's workhorse is the built-up roof (BUR) system. Coatings commonly used on BUR systems include solvent- and water-borne asphalt coatings; solvent- and water-borne aluminized asphalt coatings; and water-borne white elastomeric coatings (generally acrylics).

View fullsize

BUR systems can have several surface finishes—they can have bare or glaze-coated top sheets; be flood-coated with mopping asphalt; have a mineral (granulated) cap sheet as a top layer; or have a finish layer of gravel embedded in hot asphalt.

A mineral cap sheet generally is the easiest surface to coat because its small texture allows most coatings to achieve a strong mechanical grip. These minerals also block asphalt bleed. Smooth BUR systems are readily coated with solvent-borne asphalt coatings; they require careful preparation and base coats to accept water-borne coatings. Gravel-covered roofs generally are impractical to coat without removing the gravel, which will affect a roof system's fire rating.

Asphalt coatings, long recognized as effective for prolonging life cycles and restoring aging BUR systems, are applied after a BUR system's initial installation and at regular intervals during the BUR system's life cycle as part of a regular maintenance program.

Traditional solvent-borne bituminous roof coatings are made from cutback bitumen. To make cutback bitumen, distillate bitumen residue is refined to various specific physical properties through vacuum distillation or oxidation. This refined asphalt then is blended with a petroleum solvent, such as mineral spirits. This blend of bituminous resin and solvent is combined with special clay fillers or fibers to create a gel coating. These components' proportions ultimately determine a coating's consistency and properties.

For the past 60 years, water-borne asphalt coatings have been developed and used as alternatives to solvent-borne coatings. The mixture of bitumen, water and bentonite (clay) is referred to as asphalt emulsion because the microscopic asphalt particles are held in suspension by a clay coating.

In an ongoing, independent coating durability test program conducted by the Midwest Roofing Contractors Association it was observed that solvent- and water-borne coatings in all climates perform better on all types of smooth roof surfaces when applied over an asphalt emulsion base coat. One advantage of asphalt emulsions is they generally meet fire ratings of original asphalt BUR systems.

If an original roof system was applied in hot asphalt, an asphalt emulsion coating generally can be applied relatively soon, but if the original roof was cold-applied with an adhesive, it usually is necessary to wait about 30 days before applying an asphalt emulsion.

Aluminum pigments can be used to formulate solvent- and water-borne asphalt coatings to protect against ultra­violet (UV) radiation and provide significant reflectivity. These coatings have small flakes of aluminum pigment dispersed in them. They typically have solar reflectivity values between 0.40 and 0.50 though premium formulations have demonstrated initial solar reflectivities in excess of 70 percent.

Highly reflective white top coats have become more common during the past several years as a means to reduce peak roof surface temperatures. This minimizes peak electrical demand for air conditioning in many buildings and provides ultimate reduction in diurnal temperature cycles, which can stress and fatigue roof systems.

A majority of these white coatings are water-borne acrylic coatings. Because of the range of physical and chemical properties available within the general acrylic category, a particular coating's suitability for a given substrate should be verified with the coating's manufacturer. Most white acrylic coatings intended for use on asphalt roof systems can be applied directly to mineral cap sheets after appropriate surface cleaning (some don't require a barrier layer); smooth asphalt surfaces normally require a specified primer or base coat designed specifically to stop asphalt from bleeding into the top coat.

Asphalt typically contains light oils called exudates, which rise to a membrane's surface soon after application. Exudates often wash off roof systems after a rainstorm. Nevertheless, any exudate that remains on a roof system before coating application should be thoroughly removed. Exudates can cause staining or even debonding of a coating.

An optional coating for a gravel-surfaced BUR system is spray polyure­thane foam (SPF). This effectively changes a substrate from gravel-surfaced BUR to SPF. An advantage of this approach is the layer of insulation above the BUR keeps the BUR from being subjected to extreme heat. A white coating over an SPF roof system can result in additional energy savings. Typical coatings for SPF are acrylic, polyurethane and silicone.

Whitening of the existing base of a commercial BUR system is important. Although BUR systems are among the most durable roof systems available, it is possible to extend their life cycles even more with coatings.

Source: Professional Roofing