How to Choose the Most Effective Roof Coating
Comprehensive preparation, application, and maintenance ensures that coatings extend roof performance life.
Roof coatings are essential tools in repairing roofs and extending roof performance life, but realizing these benefits goes beyond specifying the most effective coating. Maintenance and engineering managers also need to pay attention to the post-application phase of a coating’s life.
Roof coatings are monolithic, fully adhered fluid applied roofing membrane, or non-membrane. They can stretch and return to their original shape undamaged as long as they are not stretched beyond their elastic limit and tensile strength. Managers need to consider these two characteristics, as well as breathability — moisture and water release — ultraviolet (UV) reflectivity, and permeability when specifying the most appropriate product for the job.
By understanding the costs and benefits of roof coatings, managers will be better able to specify available products to meet facility needs, and they will be able to provide training that ensures quality installation and a long performance life.
Roof coatings are an excellent way for managers to meet the challenge of delivering a roof that offers long performance life and sustainability at optimum cost. Sustainability in the case of roofing means meeting current demands while ensuring future needs also can be met.
If roof management programs waste materials while adding to pollution, increasing cost, and reducing future supplies, managers will need to rethink these activities to achieve sustainability. Coatings extend the performance life of the roof at a cost far below that of a new roof substrate.
Since roof coatings can be applied over the existing roof, no tear-off is required, which shortens the job in many cases to one day. And coatings can be applied on top of an overlay, extending the life of the overlay.
The cost of roof coatings is usually classified as an expense and is written off in the year it is installed, unlike a new installation, which is a capital improvement and must be amortized over several years. This is a major immediate benefit, so it pays to get financial advice to make sure the organization realizes all the benefits.
Making a match
Each roof coating has special characteristics, but no coating has all the features, so it is important for managers to prioritize which properties are required for their specific installation and specify the coating or combination of coatings that gives the best service.
Synthetic rubber is very tough. A 60 to 80 mil thickness has 1,100 percent elongation, 700 psi tensile strength, and 0.1 perm, which is a unit of moisture and water absorption. The lower the number, the more water and moisture penetration resistant. Synthetic rubber resists ponding and hail, and is durable, renewable, non-breathable, and black in color.
By comparison, silicone at 20 to 40 mils has 150 percent elongation and high reflexivity and resists ponding water. At 330 psi tensile strength, it tears more easily and is harder to repair.
Acrylic elastomeric coating at 20 to 40 mils has 300 percent elongation, 150 psi tensile, 8 perms, high reflectivity, and UV protection, and it is sustainable but does not resist ponding water well. It flexes up to 250 percent with roofing to resist damage and leaks, it reflects heat and UV rays to reduce interior temps, it can be applied over metal, tile, some single-ply, and built-up roofing, it can add 10 to 15 years to roof life, and it leans up with water. A 5-gallon container covers up to 500 square feet.
Changing a roof’s color to match the environment can produce major energy savings. A black coating in cold climates absorbs the sun’s heat, reducing heating cost, while a white roof in warm climates reflects the sun’s heat, reducing indoor temperatures and saving cooling energy. For this purpose, a white top coating is used if the base coating is black for heat reflection.
Some coating-deck combinations can be troublesome. For example, when using an acrylic coating over a tin roof, the acrylic acts like paint and will crack and bubble as it ages. These defects can allow water to seep under the coating and lead to rusting metal and fasteners. It can even lead to ice buildup in cold weather under the coating, where it can go unseen and degrade the deck over time.
Cold-press asphalt emulsion at 40 to 100 mils has 50 percent elongation, 100 psi tensile, and 2 perms. It is effective as a base coat but tears easily and needs reinforcement.
In some cases, managers can combine several products to achieve the desired coating objectives. For example, silicone rubber offers high-tensile strength and high elongation but low UV reflectivity. Combining it as a basecoat with an acrylic topcoat that offers UV reflectivity creates an effective coating when all these characteristics are needed.
Building movement happens due to freezing, thawing, and wind forces. They are high force, short distance moves, so the roof coating can have low elongation properties, but must have high tensile strength.
Non-destructive testing during the job verifies that the installation follows standards to give the rating coverage and coating life. Before coating application, the preparation of the deck must follow manufacturers recommendations which are based on standard codes. Moisture meters assure the deck is dry enough for application of coating. Standard surface roughness samples give a comparison to achieve the right bonding needs. And thickness meters ensure proper coating dry thickness results.
Training and maintenance
A roof coating that is properly specified, applied and maintained can add 20 years to a building’s roof system. Optimum quality assurance starts with training, research, and development, and it includes analysis of the roof, product selection, installation, and maintenance.
Regardless of warranty terms, a well-trained staff can ensure optimum sustainability at each of these stages. This process can mean 500 hours of training or more at each stage. Knowledge of product limits and compatibility with the roofing on which coatings are applied is an essential part of the training that in-house and contract installers must receive for best results.
Training is essential to make sure every phase of a roof coating project is done in a safe way that yields all potential benefits without waste. Training programs offer safety guidance, such as: no smoking where flammable products are used and stored; slippery products when wet; and proper personal protective equipment is required.
Managers have access to a host of sources for roof coating training. Manufacturers and contractors can provide videos, while some are available free online or included with the product. Classes also are available online and in the classroom. This is money well spent because a roof coating application is a complex undertaking that requires many hours of training to ensure quality and cost benefits.
A maintenance plan outline with scheduled dates for each step can deliver exceptionally long roof life. As an example, consider this annual maintenance plan for the first 10 years after application:
Check and clean gutters annually.
- Clean dirt, especially from ponding and transitions, such as from the deck to the parapet wall.
- Look for causes of ponding, and correct the conditions.
- Power wash the roof when it becomes dirty or discolored.
- Repair cuts, loose flashings, penetrations, and seams as identified to keep moisture and water from penetrating.
- Keep a log of all roof maintenance to support warranty claims.
Next consider maintenance at about the tenth year:
- Check coating thickness to determine loss.
- Rebuild ponding areas to improve draining.
- Reinforce penetrations where they are loose, cracked or pulled away.
- Recoat the whole roof.
Guidance provided by codes and manufacturer’s recommendations are essential to getting the optimum performance life from a coating. The codes are based on destructive testing, and the manufacturer’s recommendations are the guidance that achieves meeting the code standards for a coating life cycle. All products specified should be reviewed to make sure they comply with the proper codes and standards.
Thomas A. Westerkamp is a maintenance and engineering management consultant and president of the work management division of Westerkamp Group LLC.