Roof Coating Options

1. Bitumen-Based Coatings – these come in a wide variety of formulations. They can be water or solvent – based. Generally these are the lowest cost options for application to most roofing surfaces. Coal tar based coatings produce outstanding water – resistant properties. Bitumen coatings generally need to be reapplied every three to seven years.

2. Acrylics – available in water-base and solvent formulas. Good reflectivity when properly formulated, excellent weathering. Many properties are variable depending on formula and, generally, the higher the cost, the more favorable the performance level. Properties to consider are adhesion, low temperature flexibility, bleed through of underlying surface, VOC levels, cure time, and many others.

3. Urethanes – these products are some of the newest to make an impact in the roofing market. They generally perform at the high end of the scale when compared to the other available coatings. The price for this performance is higher initial cost. There are countless urethane variations and review of all the options available is beyond the scope of this review. In general the nature of urethane chemistry allows for the formulation of superior performance properties and overall value to the customer.

4. Epoxies - once again, the choices in epoxy-based products for roofing application is overwhelming. In its basic form epoxy provides a hard and tough finished product which is excellent for flooring applications. To be used in roofing, epoxy polymers must be formulated in ways which result in improved flexibility, elongation and fatigue to accommodate the greater movement cycles in roofing. One highly effective modifier for epoxy is coal tar which results in excellent long term water resistance and repellency.

5. Polyureas - these products in a general way are related to polyurethanes but are based on chemistries which yield a unique coating in terms of cure time, strength and crack-bridging and elongation. Their high strength properties make them best suited for strong stable substrates such as metal and concrete. They also require specialized equipment for application.

Coating selection for Various Roof Surfaces

Bitumen-Based Roofing Ensembles:

On Asphalt Roofs the commonly used coatings are:

• Solvent-based and water-based asphalt coatings

• Solvent-based aluminum asphalt coatings

• Water-based white elastomeric coatings with predominance of acrylic products. Although urethane products are making a significant impact

more recently.

On Coal Tar Roofs, the coating products typically used are solvent-borne coal tar coatings with a re-application of gravel due to the flow characteristics of these type of coatings. Coal tar coatings have been successfully applied to aged asphalt roofs with excellent results.

White acrylic latex coatings have been used with significant success on smooth surface asphalt roofs. It is important to select the right product or product combination for this application. Some acrylics have a tendency to allow bleed through of the asphalt over which they are applied. Technical advancements have allowed some acrylic formulas to be developed which resist this from occurring. Of course, there is some added cost for this performance.

There are also bleed-resistant primers which can be employed or an asphalt emulsion can be applied and allowed to fully cure prior to applying the white acrylic coating.

On gravel roofs, sprayed in place polyurethane insulation has been used once the roof is cleaned of all loose, unembedded gravel. The urethane insulation then can be coated with any number of white reflective products.

Modified Bitumen Roofs

The modified asphalt products now available use either SBS (styrenebutadiene-styrene) rubber or APP (atactic polypropylene) thermoplastic polymer to improve the properties of the starting bitumen material. The options for coating modified bitumens are much the same as those for built-up roofing membranes. Solvent-borne and water-based asphalt coatings can be used as well as aluminized products. Acrylic latex materials are often used and are particular useful on granule-surfaced modified sheets because of the coating being “locked-in” by granule texture. With the other solvent-based white coatings available, bleed is a factor to consider. It is always advisable to perform a bleed-through test to confirm acceptability. Otherwise, some type of blocking primer or base coating should be used in the specification.

Coatings for Single Ply Elastoplastic Products

For some time, one of the main arguments used against the rubber and thermoplastic single ply membranes was that they could not be maintained. This point of view has changed drastically based on technical advances in coatings and experience with past applications. Prior to coating these membranes, it is critical to perform all the necessary repairs and upgrades regarding seams, flashings and any other observed problems or potential problems.

The inventory of single ply roofs with a potential for maintenance coatings is overwhelming. The economic situation has prodded many building owners to delay complete replacement programs. This creates an opportunity to provide a technique which extends the membrane life a few more years. Coatings fill this role especially if the membrane is properly prepared prior to application. Black EPDM roofs, for example, can be surfaced with white coatings which lessen the temperature stresses which are experienced and add extra years of useful performance.

The attractiveness of this market has resulted in a myriad of coatings being promoted for single ply maintenance applications. Great care should be exercised in selecting the proper products for this important budgetary decision. It appears the market is primarily focusing on acrylic, silicone and urethane material Each of these technologies has its advantages and disadvantages.

Acrylics, for example, are the most economical but the products available have great differences in properties and performance. Required preparation, adhesion properties, flexibility and weathering characteristics are key in selecting a product. Since primarily the water-based forms of acrylics are employed, weather is an important factor in the application process. High humidity, cold temperatures and impending rain can be serious problems for these coatings. Additionally, water-based acrylics should only be used on roofs with good drainage as ponding water is a major issue for these products.

Silicones appear to be a compromise of cost and performance. The number of suppliers of this product has significantly decreased in recent years. The greatest issue with silicones has been tentative adhesion on some substrates. A silicone application can only be recoated with another silicone material as other coatings will not adhere to it.

It should be pointed out that some single ply membranes present adhesion difficulties. A test patch of the coating material should be applied to determine if it a suitable products for the membrane especially if it is an EPDM, TPO or PVC.