If you’re familiar at all with roof coatings, you know what a lifesaver they can be. With the right roof coating, applied properly, your roof can last almost indefinitely.
But that’s the question, which coating is the right one?
At Gideon, we’ve installed every kind of roof coating over the last 20 years, including both acrylic and silicone, and we’re intimately familiar with the benefits and downsides of each. At the end of the day, your choice depends on what kind of building you have, what it’s used for, what kind of weather you experience, and what kind of budget you have.
In this article, we’ll dive deep into the question of acrylic vs silicone roof coatings, so you can make the right decision for you.
Acrylic roof coatings are a protective sealing membrane and UV ray blocker applied to roofs (mostly commercial flat roofs and metal roofs) to protect them from the elements, including sunlight, rain, and wind.
The primary component is the acrylic polymer, a type of synthetic polymer well-known for weatherability, UV radiation resistance, and its ability to maintain its physical properties over a wide range of temperatures.
The basic chemistry of an acrylic coating includes a mixture of solids like limestone, acrylic polymers, surfactants, water, and a sun-blocking ingredient similar to what’s found in sunscreen for the beach. When the water evaporates after application, the remaining ingredients form a flexible film that protects an existing roof system and adds a redundant layer of protection.
Silicone roof coatings are another form of liquid-applied solutions, crafted predominantly from silicone polymers and crushed rocks. They are well-known for their industry leading weatherability and superior resistance to the elements. In fact, silicone coatings are the most UV stable products in commercial and industrial roofing.
Let’s compare acrylic and silicone coatings on 8 measures of performance: price, life expectancy, environmental impact, UV stability, reflectivity, water resistance, ease of installation, and aesthetic appeal.
Silicone: Silicone roof coatings generally cost around 3 times as much as acrylic, so the cost differential is quite high.
Acrylic: Acrylic is by far the least expensive roof coating on the market.
Winner: Acrylic.
Silicone: Silicone roof coatings have a longer lifespan compared to their acrylic counterparts. Silicone roof coatings can last up to 50 years. Silicone Coatings are typically 90%+ solids. Those solids are essentially rocks just made into a liquid form. This is why silicone roof coatings are able to withstand harsh UV conditions without breaking down prematurely.
Acrylic: Acrylic roof coatings typically last around 10 years. While their lifespan is shorter compared to silicone, it's important to note that, like all roof coatings, they can be reapplied and refreshed every 10 years, keeping your roof protected indefinitely. Also, if multiple passes are added to form a thicker membrane, acrylic roof coatings can last upwards of 20+ years.
Winner: Silicone. When comparing the lifespan of acrylic and silicone coatings of the same thickness, silicone coatings will outperform acrylic coatings 3-1.
Silicone: Because silicone coatings are solvent-based, they have traditionally been much higher in VOCs (volatile organic compounds) than acrylics. However, recent years have seen the rise of “high solids” silicone coatings. These contain a higher percentage of solid material compared to previous formulations, meaning less solvent is used, thus reducing the amount of VOCs emitted during application.
Another factor to take into account when considering environmental impact is lifespan. Silicone’s environmental impact is partially reduced compared to acrylics simply because fewer coats of it are needed to achieve the same degree of protection.
Silicone roof coatings are made with two different chemistries known as Oxime and Alkoxy. One major difference between these two chemistries is the volume of VOCs they release. The Oxime recipe is used by all silicone coating manufacturers except a small few and it releases Methyl Ethyl Ketoxime, a known carcinogen, whereas the Alkoxy recipe is formulated to release Methanol (non-carcinogenic), is solvent free, and is neutral to the air and surrounding environment, producing little or no odor.
Acrylic: Acrylic coatings, while needing more coats and more frequent replacement, are water-based rather than solvent-based, and have lower VOCs, making them a more environmentally friendly option. In addition, acrylic roof coatings retain their white color, while silicone very rapidly turns brown (within a single month). This loss of white color reduces silicone’s reflectivity, which may result in higher HVAC usage, and therefore greater environmental impact.
Winner: Slight edge to acrylic.
Silicone: Silicone coatings provide exceptional UV resistance, making them excellent for areas with high sun exposure. They are less prone to chalking and degradation due to UV radiation.
Acrylic: Although acrylic coatings also offer UV resistance, they will degrade and chalk more quickly over time.
Winner: silicone.
Silicone: Silicone coatings have high reflectivity, which can effectively reduce heat absorption and lower energy costs. However, they absorb dirt and other residue, which will rapidly turn them an ugly brown and reduce their reflectivity.
Acrylic: Acrylic coatings are highly reflective as well and can significantly contribute to energy efficiency. They largely maintain their reflectivity over the lifespan of the coating, as they don’t absorb nearly the same volume of dirt as silicone.
Winner: acrylic.
Silicone: Silicone is impervious to ponding water. It will not become saturated even under long-standing ponding water.
Silicone is able able to withstand ponding water that exceeds the National Roofing Contractors (NRCA) standard of "no more than a ¼” of water remaining in an area less than 99 square feet within 48 hours after the last rain."
Acrylic: While acrylic coatings offer good general water resistance, they aren't as effective in areas with persistent standing water. If the existing roof suffers from ponding water that is 1/4" deep or greater (and sitting on the roof longer than 48 hours) it will break down prematurely.
To avoid this, a polyester scrim can be added to provide structural stability within the coating or silicone coatings can be applied to select areas that present the highest risk of ponding water.
Winner: Silicone.
Silicone: Silicone coatings can gum up application equipment and require mineral spirits to clean, so installation is usually more difficult than acrylics.
When using spray equipment it can be very hard to avoid “overspray” onto cars or other inventory near the building - and removing silicone overspray is extremely difficult and costly. Another factor is the need to flush the equipment after each day’s use. If flushing is done poorly, the equipment can become unusable overnight, requiring workers to take the equipment apart and clean it. It can also be difficult to procure the mineral spirits needed to flush the silicone.
Silicones can be applied at whatever thickness you want. You can safely apply a 1 foot thick pass of silicone and it will cure without fail. This allows for fewer coating layers, which can bring the labor costs down.
A big advantage of silicones is that, unlike silicones, they can be applied below 45-50 degrees. This allows building owners to be more flexible regarding their project timeline.
Another installation advantage of silicone is that it is a “moisture cure”. The more heat and humidity in the air, the faster the coating will “set”. This helps to avoid run-off.
Acrylic: Acrylic coatings are easier to install, generally speaking, because they are easier on application equipment and can be cleaned up with water. Because they are water-based, however, they cannot be applied in temperatures below 50 degrees fahrenheit.
Acrylic coatings can be left in the spray equipment overnight, avoiding the need to flush the pump and lines with chemical solvents like mineral spirits. This saves setup time and eliminates the risk created when silicone isn’t flushed properly.
Overspray is far less of a concern with acrylic coatings. Even if it occurs, the atomized mist of coatings will dry before it lands on any objects below the roof - and thus won’t stubbornly stick to anything, unlike silicone. It will dust off like the dust from a gravel road.
Winner: acrylic.
Silicone: Both silicone and acrylic coatings can come in a variety of colors, silicone will tend to lose its color over time due to its tendency to accumulate dirt.
Acrylic: Acrylic coatings will usually retain their color much longer and accumulate less dirt, so they’re generally the superior aesthetic choice. At GIDEON, we have special acrylic finish coat products that withstand extreme UV conditions and will retain their rich color for up to 20-Years. These finish coats have more color options than silicone as well.
Winner: Acrylics.
So, now that you have a good grasp on the differences between silicone and acrylic coatings, how do you know which is the best choice for you? Ultimately, it comes down to your particular roof and business goals, but here are some guidelines:
Roof coatings are a great choice for restoring your roof, but solid information is sparse. It can be daunting to decide on the most suitable coating for your roof.
Now that you’ve learned about the major differences between acrylic and silicone coatings, reach out to us at GIDEON for a free 30 minute consultation. Every building and situation is unique, and we can offer tailored advice, based on our years of experience and your specific circumstances, to help you get the solution that’s right for you.