The Pros & Cons of Elastomeric Roof Coatings

It's an all-too-common scenario: you learn that your commercial roof warranty is about to expire, but the roof is still in decent shape. You've done some repairs over the years, but there are no leaks or serious damage. You wonder, "Do I really have to replace a basically good commercial roof?" 

Fortunately, you may not have to. Elastomeric roof coatings may be able to save your roof and your money. But roof coatings are a polarizing topic in the industry. Some contractors will tell you they're a terrible product and a waste of money, while others swear by them. 

How do you know if they're a good choice?

Few companies know as much about roofing as GIDEON. Since 2002, we've installed millions of square feet of almost every type of commercial roofing system. In this article, we'll discuss the pros and cons of elastomeric roof coatings, so you can decide whether they are the right choice for you.

Table of Contents

• What Are Elastomeric Roof Coatings
• Pros of Elastomeric Roof Coatings
• Coatings Can Extend the Lifespan of Your Roof 
• Roof Coatings Can Help You Save on Your Energy Bill
• Coatings Cost Less Than a New Roof
• Cons of Elastomeric Roof Coatings
• Overspray
• Roof Coatings Can't Be Applied in Certain Weather Conditions.
• Coatings Are Not Compatible with Every Roof System
• Not All Coating Crews Are Experienced

What Are Elastomeric Roof Coatings?

An elastomeric roof coating is a fluid coating that cures into a seamless, durable, and highly flexible membrane. The fact that it starts as a liquid makes it easy to apply to a roof, while its elasticity means it can stretch and revert to its original shape without breaking. Modern roof coatings are made from acrylic, silicone, rubber, and urethane, each with its own advantages and disadvantages. 

Pros of Elastomeric Roof Coatings

Coatings Can Extend the Lifespan of Your Roof 

They say that everything breaks down with time. But it isn't time itself that erodes building materials. It's the elements. Water, wind, and - above all - sunlight slowly eat away at virtually every man-made material. This is why a traditional, uncoated roof system has to be replaced every 20-25 years.

Roof coatings shield your roof from the relentless assault of the elements. The seamless barrier they create seals the roof from rain and the sun's damaging rays. This barrier "locks your roof in time," extending its life by another 15-20 years for a fraction of the cost of a brand-new roof.

Resistance to sunlight is one of the key properties of elastomeric coatings. Ultraviolet radiation leads to cracking, fading, and other forms of deterioration on exposed roofing materials. The elastomeric polymer from which roof coatings are made reflects and absorbs these harmful rays, so the underlying substrate doesn't. 

Leaks are the most common roofing problem you hear about since they're usually the first time you notice something is wrong. Leaks often occur at seams and penetrations in the roof. A seam is where two separate roof system components come together. A penetration is anything that sticks through the roof, like a pipe or an HVAC unit. Terminating metal, screws, adhesives, and other fasteners must be used to make penetrations watertight in conventional roofing systems. This system creates many "points of failure" that can leak as the roof ages. 

Elastomeric coatings cover the entire roof system with a seamless membrane that prevents water from "seeping through the cracks ." The liquid covers, fills in, and waterproofs all seams and cracks.  

Another common problem on commercial flat roofs is "ponding," which is exactly what it sounds like - when water sits on top of the roof for long periods and creates a small pond. Ponding eventually breaks down the underlying material and causes leaks. High solid coatings (called silicones) are impervious to ponding water. When they're properly installed, water can't break through. Additionally, before the coating is applied, the contractor can level out the roof, which will eliminate any pre-existing ponding tendencies on the original roofing system.

And not only are coatings waterproof, but they're also highly resistant to water vapor in the air. Acrylic coatings have a vapor permeability of 14%-15%; while urethanes and silicones by 4-6%; and rubberized and polyurea are perfect vapor barriers, with 0% permeability. But you only sometimes want an airtight barrier, as some underlying roof materials, like wood or cinder block, need airflow. Acrylic or silicone is a better choice for such materials. 

Roof Coatings Can Help You Save on Your Energy Bill

Roof coatings can also lower your utility bill. Because white roof coatings reflect the sun's rays, your roof will absorb less heat, which reduces your HVAC load. A traditional, uncoated roof can reach temperatures up to 180 degrees in the summer. By contrast, the temperature of a coated roof may only go up to 110 degrees, a reduction of more than 40%. 

A darker color may be the better choice for a roof coating in a cooler climate since helping the building retain heat is more important than keeping it out in a place with long winters and short, cool summers. In this case, a gray or black coating may be more appropriate.

But where coatings really help you save on energy bills is when they are used in conjunction with spray foam insulation. Also called "foam roofing," spray foam insulation is one of the most energy-efficient materials in the world. This superior efficiency is due, in large part, to the fact that the spray foam creates a monolithic membrane. The poly iso, in contrast, is installed in multiple rectangular sheets, creating seams through which thermal energy can move. 

Research by Texas A&M has shown that the energy savings generated by spray foam insulation can pay for its cost within 4 to 5 years.

In the same vein, roof coatings are very environmentally friendly. Not only can they reduce energy usage, but they are also made from materials that are low in the emission of Volatile Organic Compounds (VOCs) and free from chlorofluorocarbons (CFCs).

Coatings Cost Less Than a New Roof

Roof coatings require a lot less labor and material than a new roof. 

A new roof requires roofers to carry the materials onto the existing roof and then assemble and fasten them. This process requires a large staging area and often a large crane. Legally, you can have up to two roof systems on one building, so you may not have to remove the existing roof. But if you already have two systems stacked on each other, a labor-intensive tear-off and waste removal may be necessary. A tear-off comes with its risks, the primary one being leaks. At the end of each day, the roofers have to seal the seam between the new and old roof, a process called "drying in ." If this isn't done correctly, you are at risk of leaks and flooding. 

In contrast, elastomeric roof coating installation is much simpler. The roof must be thoroughly cleaned beforehand, after which the coating can be rolled or sprayed on. The coating does not have to be carried up to the roof; it can be pumped up with a machine. And a roof coating is not legally considered a second roofing system, so there's no need for a tear-off. 

Overall, roof coatings require less material, labor, and time, which translates into savings for you. These savings are the biggest reason building owners often choose coatings. When their roof is getting closer to the end of its lifespan, a coating can extend that lifespan by 10-25 years for a significantly lower price than a new roof. For example, a roof replacement may cost between $6-$15 per square foot. A roof coating system, by contrast, will generally run between $3-$7 per square foot. In addition, at the end of a coating's lifespan, you can apply a maintenance coat for half the price of the original coating system, which renews it and its warranty for another 10-20 years. 

Cons of Elastomeric Roof Coatings

Overspray

Spraying is a standard method of application for elastomeric coatings. When this is done, "overspray" can occur, which is when the wind blows the spray off the roof and onto objects below. Trying to remove overspray from vehicles or other buildings is not a situation you want to be in.

Acrylic coatings dry in the air as they fall, so, fortunately, they won't stick to anything. But silicone, urethane, and rubber coatings will not dry until they hit a surface, and they are tough to remove. Overspray also floats very far through the air, "like cottonwood trees," as our founder, Eric, likes to say. To eliminate overspray, roofers can use special screens or spray inside a portable "spray tent ." You can also move cars out of the parking lot. 

If overspray is a significant concern, an easy way to eliminate it is to simply…not spray the coating. A good contractor can roll the coating on most roofs instead of spraying.

Roof Coatings Can't Be Applied in Certain Weather Conditions.

Water-based coatings (acrylics) can freeze, so you cannot apply them once the temperatures go drop into the 40s Fahrenheit. 

Moisture can also cause installation problems, of which morning dew is the biggest. Dew starts settling in during the evening as temperatures drop. If the dew settles onto the roof during application, moisture will get trapped underneath the coating, and the coating will bubble and blister when the sun rises in the morning. Inexperienced crews often fail to get the dew off the roof before starting work in the morning, or they'll continue coating into the evening hours.

Coatings Are Not Compatible with Every Roof System

Some roofing substrates, such as tar and gravel roofs, may not be compatible with elastomeric coatings. To guarantee that the coating adheres and offers adequate protection, contractors need to use certain kinds of primer or other preparation processes. The elastomeric covering may not bind properly without proper preparation, resulting in delamination, peeling, or blistering.

Some roofs may also be too old or too damaged to accept a roof coating. A competent installer will do a thorough inspection beforehand to determine your roof’s eligibility. 

Not All Coating Crews Are Experienced

Unfortunately, not all coating crews are good at their craft. Without the proper equipment and expertise, your coating may not adhere properly, resulting in roof leaks, insufficient coverage, and many other issues. 

Surface preparation beforehand is critical. The coating must be applied to a clean, dry, and sound substrate for a uniform appearance and long-term adhesion. Before application begins, contractors must clean the roof thoroughly, remove any debris or loose material, and make any necessary repairs.

Getting the right thickness and coverage is also essential. If the coating is applied too thinly, it won't offer enough protection, and if it is applied too thickly, it will dry unevenly and cause other problems. A thin coating will deteriorate before the warranty period ends. A thin coating may also absorb too much moisture, which can cause adhesion failure. 

The Upshot

If you want to save money and extend the lifespan of your roof, elastomeric roof coatings can be an excellent choice. Still, it's critical to properly assess whether a coating will work on your current roof, grasp how coatings work, and hire competent, professional installers. 

Now that you've learned the pros and cons of coatings, I'd recommend checking out our guide to TPO roofing, which is often the alternative you’ll be presented with by a contractor. In this comprehensive guide, you'll learn everything you need to know about TPO.