Installation guideline tips for roof coating

By Cotney Consulting Group.

Learn best practices for roof coatings in order to protect and extend the useful service life of existing roof assemblies.

Coatings, while considered a reasonably modern process, are one of our industry's oldest forms of waterproofing, whose ancestral roots date back to the Egyptians around 3000 BC. They used various mixtures of natural products to waterproof their boats. By 1000 BC, they further develop their coatings by creating varnishes from natural gums. Other cultures also developed coatings and started adding colors to the mixtures, and between the 1st and 2nd century BC, coatings started to be used to waterproof and decorate dwellings.  

In Germany in the late 1600s, a chemist develops a procedure to use the stickiness of pine coal tar as a protective coating on wood and natural rope products. This process gave birth to more modern organic, inorganic and synthetic coatings developed during the 19th and early 20th Centuries. Within the last 40 to 50 years, the development of polymers in coatings is the scientific advancement that has taken us to where we are today in the roof coating marketplace.   

What are roof coatings

This article will not cover a cold-applied roof system consisting of liquid coatings/adhesives and membrane reinforcement. We are discussing roof coatings designed to protect and extend the useful service life of existing roof assemblies, such as BUR, Metal, Modified Bitumen, Single-Ply Membranes and SPF.

Roof coatings should not be confused with paint products; coatings are thicker than paint and have a higher solid content. Roof coatings are specially formulated to protect roofs from the damaging effects of weather and the environment. The quality and volume of resins added during manufacturing allow the coating to maintain elasticity throughout its lifecycle. Coatings are also applied in manufacturers' recommendations of multiple gallons per 100 square feet, unlike paint, typically used in portions of a gallon per 100 square feet.

Four common types of roof coatings

The most common types of roof coatings used in roofing today are acrylic coatings, asphaltic coatings, polyurethane coatings and silicone coatings.

1 - Acrylic coatings

Acrylic coatings are water-based and ideal for high UV environments with a desired reflective roof. They can also be easily colored by adding different pigments. Acrylic systems are usually less expensive than other coating options and easy to install, making them popular among contractors and facility owners.  

Acrylic Coatings are negatively impacted by ponding water and will affect the overall performance of the system. Acrylic Coatings should only be used on sloped roofs with adequate drainage. These coatings are also a water-based product and should not be allowed to freeze during storage. At the time of application, the outside temperature must be at least 50°F (10°C) and rising for the coating to properly adhere to the roofing substrate.

2 - Asphaltic coatings

Asphaltic coatings are either solvent-based "cutbacks" or emulsions. They are usually black or aluminized and suitable for cold and inclement weather. Aluminized coatings provide a reflective and UV-stable asphalt coating when required. 

These coatings must only be used over an existing roof system compatible with asphalt solvents and emulsions. 

3 - Polyurethane coatings

Polyurethane coatings are typically solvent-based and have favorable mechanical properties and high abrasion resistance. The base coat product is of the aromatic family, and the topcoat is aliphatic, which is UV stable, holds its color and resists dirt pick-up. Urethanes also provide excellent protection from hail and high-traffic roof areas.

Polyurethane coatings emit a strong odor. The odor is not harmful, but care must be taken to prevent the order from entering a facility's fresh air intake system and disrupting the building's occupants.  

Shelf life is a concern with single-component urethane coatings, which are continually curing — even in the pail. Two-part urethane coatings will not cure until mixed.

4 - Silicone coatings

Silicone coatings perform well in high UV environments with a desired reflective roof. Silicones are often used where rain is a daily occurrence compared to other coatings that require prolonged curing before they can be exposed to moisture. Silicon, a moisture-cure substance, makes it an excellent choice to protect against the damaging effects of ponding water.

Silicones easily attract dirt and other airborne particles, so over time, this accumulation of dirt and dust on the roof surface causes the system to lose its reflective properties. Most manufacturers recommend a silicon coating to be pressure washed within 6 to 12 months of installation, which helps eliminate the problem of future dirt accumulation. 

After curing, Silicone Systems become very slippery when wet. It is recommended that a well-marked (different color) granulated walkway path is provided to roof areas such as roof access points, HVAC units, other equipment, roof edges, etc.

Other types of coatings

Other roof coatings are made with different resins or combinations of resins. These can include, but are not limited to, butyl resins, fluoropolymer, PMMA, polyester, silyl terminated polyether (STPE), polyuria, PUMA, SEBS and styrene-acrylics.

These coating systems are gaining popularity, especially for custom roofing applications and detailed requirements. Refer to the specific manufacturers' recommendations for these systems for detailed installation instructions and precautionary guidelines. 

Roof surface evaluation and preparation  

Before starting a roof-restoration project, you must thoroughly inspect the existing roof conditions and ensure the existing roof is a proper candidate for coating.  

Using infrared technology will assist in locating wet insulation, which will need to be removed and replaced. Once your crews remove the wet insulation and install the new membrane, they can begin surface preparation and any other necessary repairs before the coating application.

The roof must be thoroughly cleaned, and a pressure washer must be set at the proper setting so as not to damage the existing roof. Depending on the surface, the condition will determine the best solution mix for cleaning. Always rinse the cleaner thoroughly and allow it to dry before proceeding with the coating application. Proper preparation is a critical step to ensure a successful coating application. Always refer to the coating manufacturer you are using for their specific requirements for roof preparation.

Depending on the coating type as outlined above and the surface you are coating, you will need to refer to your specific manufacturer's installation guidelines and instructions for the proper application methods and coverages you will need to use.  

Like any other roofing project, a roof coating project will only be successful if you follow proper roofing practices. Always inspect the roof surface to ensure it is suitable and qualified for a restoration installation, and then select the appropriate coating product. Properly prepare the surface and install the product according to the manufacturer's quality guidelines. You will deliver a quality and long-lasting coating application to your clients.