How to Choose the Most Effective Roof Coating
Extensive preparation, application and maintenance ensure that coatings extend the life of the roof.
Roof coatings are essential tools for repairing roofs and extending roof life, but achieving these benefits goes beyond specifying the most effective coating. Maintenance and engineering managers should also pay attention to the post-apply phase to extend the life of a coating.
Roof coatings are monolithic, fully adhered, liquid applied roofing 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 must consider these two characteristics, as well as breathability – moisture and water release – ultraviolet (UV) reflectivity and permeability when specifying the most suitable product for the task.
By understanding the costs and benefits of roof coatings, managers will be better able to specify available products to meet facility needs, and provide training that ensures high-quality installation and longevity.
Roof coatings are an excellent way for managers to meet the challenge of delivering a roof that offers longevity and durability at optimum cost. Sustainability in the case of roofing means meeting current requirements and ensuring that it can also be provided for in the future.
As roof management programs waste waste material while increasing pollution, increasing costs and reducing future inventories, managers will need to rethink these activities to achieve sustainability. Coatings extend the life of the roof at a cost that is well below that of a new roof substrate.
Because roof coatings can be applied over the existing roof, there is no need to tear off, shortening the job to a day in many cases. 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 amortized in the year of installation, as opposed to new installation, which is a capital improvement and must be amortized over several years. This is a great immediate benefit, so it pays to seek financial advice to ensure the organization realizes all the benefits.
Make a match
Every roof coating has special characteristics, but no coating has all the characteristics, so it is important for managers to prioritize which properties are required for their particular installation and to specify the coating or combination of coatings that will provide the best service.
Synthetic rubber is very tough. A thickness of 60 to 80 mils has an elongation of 1,100 percent, a tensile strength of 700 psi and 0.1 perm, which is a unit of moisture and water absorption. The lower the number, the more resistant to water and moisture penetration. Synthetic rubber resists puddles and hail, and is durable, renewable, non-breathable and black in color.
By comparison, 20 to 40 mils silicone has 150 percent elongation and high reflexivity, and can withstand splashing water. With a tensile strength of 330 psi, it tears more easily and is more difficult to repair.
20 to 40 mils elastomeric acrylic coating has 300 percent elongation, 150 psi tensile strength, 8 perms, high reflectivity and UV protection, and it is durable but will not withstand good running water. It flexes up to 250 percent with roofing material to resist damage and leaks, it reflects heat and UV rays to reduce indoor temperatures, it can be applied to metal, tile, some single ply and built-up roofing, it can last 10 to 15 years to roof life , and it leans up with water. A 5-gallon container covers up to 500 square feet.
Adapting the color of a roof to the environment can yield major energy savings. A black coating in cold climates absorbs the sun’s heat, reducing heating costs, while a white roof in hot climates reflects the sun’s heat, lowering the indoor temperature and saving cooling energy. A white top coat is used for this if the base coat is black for heat reflection.
Some coating-deck combinations can be tricky. For example, if you use an acrylic coating on a tin roof, the acrylic will act like paint and will crack and bubble as it ages. These defects allow water to seep under the coating and cause rusting of metal and fasteners. It can even lead to icing under the coating in cold weather, where it can go unseen and degrade the deck over time.
40 to 100 mils cold pressed asphalt emulsion has 50 percent elongation, 100 psi tensile strength and 2 perms. It is effective as a base layer, but tears easily and needs reinforcement.
In some cases, managers can combine multiple products to achieve desired coating objectives. For example, silicone rubber offers high tensile strength and high elongation, but low UV reflectance. Combining it as a base coat with an acrylic top coat that provides UV reflection creates an effective coating when all of these properties are needed.
Construction movement occurs through freezing, thawing and wind forces. They are high-force, short-distance movements, so the roof coating can have low elongation properties, but must have high tensile strength.
Non-destructive on-the-job testing verifies that the installation meets the standards to give the classification coverage and life of the coating. Before applying the coating, the deck preparation should follow the manufacturer’s recommendations based on standard codes. Moisture meters ensure that the deck is dry enough for coating to be applied. Standard surface roughness samples provide a comparison to achieve the correct bonding needs. And thickness gauges ensure a good dry film thickness.
Training and maintenance
A properly specified, applied and maintained roof coating can add 20 years to a building’s roof system. Optimal quality assurance starts with training, research and development, and includes roof analysis, product selection, installation and maintenance.
Regardless of the warranty conditions, well-trained personnel can ensure optimum durability in each of these phases. This process can mean 500 hours of training or more at each stage. Knowledge of product limits and compatibility with the roofing material to which coatings are applied is an essential part of the training that in-house and contract installers should receive for best results.
Training is essential to ensure that each phase of a roof coating project is carried out in a safe manner that delivers all the potential benefits without wastage. Training programs provide 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 variety of roof coating training resources. Manufacturers and contractors can provide videos, while some are available online for free or included with the product. Lessons are also available online and in the classroom. This is money well spent as roof coating is a complex undertaking requiring many hours of training to ensure quality and cost benefits.
An overview of the maintenance plan with planned dates for each step can ensure an exceptionally long roof life. Take as an example this annual maintenance plan for the first 10 years after application:
• Check and clean the gutters annually.
• Clean dirt, especially from puddles and transitions, such as from the deck to the parapet.
• Look for causes of urination and correct the conditions.
• Powerwash the roof if it is dirty or discolored.
• Repair cuts, loose joints, penetrations and seams as identified to prevent moisture and water ingress.
• Keep a log of all roof maintenance to support warranty claims.
Then think about maintenance around the tenth year:
• Check the layer thickness to determine the loss.
• Rebuild pond areas to improve water drainage.
• Reinforce penetrations where they are loose, torn or pulled away.
• Repaint the entire roof.
Guidance by codes and manufacturer recommendations are essential to obtain optimum coating life. The codes are based on destructive testing and the manufacturer’s recommendations are the guideline for meeting the code standards for a coating life cycle. All specified products must be reviewed to ensure they meet the appropriate codes and standards.
Thomas A. Westerkamp is a maintenance and engineering management consultant and president of the work management division of Westerkamp Group LLC.