What Is Liquid Roofing, How Does It Work?

How Do Liquid Roofs Work?

Liquid roofing systems are applied to roof surfaces in liquid form and cure to create a seamless, UV resistant, and waterproof membrane. Essentially, liquid roofs act as a sacrificial shield protecting roof substrates from the sun, rain, and other environmental conditions.

Liquid-applied membranes are ideal for both flat and pitched roof constructions and are suitable for use on a variety of materials including:

Liquid coating materials have a thicker consistency than the average household paint. They are specifically formulated with greater elongation and tensile strength so they can expand and contract with roofing substrates without becoming damaged or distorted.

Most liquid membrane roofing is applied with a hydraulic airless sprayer or tank spreader. A squeegee or nap roller may be used in certain applications.

The Origins of Liquid Roofing

The practice of liquid roofing has been around for ages, but it wasn’t offered commercially until early twentieth century.

Initially, liquid roofs were not regarded as an acceptable solution due to lack of knowledge, no access to proper training, high material costs, and supply limitations.

Most of the liquid coatings used today including silicones, acrylics, and polyurethanes weren’t introduced until the 1960s and 70s. These materials have improved considerably over the past few decades and form the basis for most modern liquid membrane roofing systems.

Increases in domestic manufacturing over the years led to reduced costs and alleviated supply chain issues.

Additionally, as roofing companies began adapting liquid roofing practices, they also began training their employees in the technology. Since liquid roofing systems require less-skilled labor than traditional roof tear-offs and replacements, companies were also able to save on the cost of training.

Perhaps one of the biggest contributors to the success of liquid roofing is the Great Recession of 2008. This period of economic uncertainty saw an unprecedented decline in new roof construction and renovation.

As a result, roofing companies were forced to downsize their workforces and seek out more practical alternatives to offer their customers. This led many commercial roofers to adopt liquid roofing out of necessity.

Since many companies had reduced workforces, they turned to liquid roofing which required less labor. Likewise, many commercial building owners and property managers sought less-expensive alternatives to completely replacing their roofs, and liquid roofing systems were the perfect solution.

Post-2008, liquid membrane roofing had established itself as an effective commercial roofing solution.

Today, liquid roofing remains one of the fastest growing segments in the commercial roofing industry with nearly every major commercial roofing manufacturer now offering their own line of liquid-applied roofing solutions.

Liquid Roof Coating vs Liquid Roofing System

The terms liquid roof coating and liquid roofing system are often used interchangeably, but there are some notable distinctions between the two applications.

Liquid Roof Coating

A liquid roof coating by itself can serve as a standalone roofing solution, but for this to be most effective, the roof must be in good to excellent condition.

The application of a liquid coating can improve energy efficiency and prolong roof life, but it’s not recommended as a long-term waterproofing solution.

Liquid Roofing System

When it comes to waterproofing, a liquid roofing system (or roof restoration system) operates on an entirely different level.

For these systems, roofing substrates are first reinforced with a combination of bonding agents, mastics, sealants, and fabric inlays. This essential “waterproofing” step is what provides liquid membrane systems with superior moisture resistance, durability, and longevity.

Multiple applications of elastomeric coating are then installed over the reinforcement layer fully encapsulating roof surfaces with a seamless, UV-resistant, and fully adhered membrane.

Additionally, liquid roof systems are covered by long-term manufacture warranties, whereas liquid roof coatings are not.

Types of Liquid Roofing Systems

The following materials form the basis of most liquid membrane roofing systems today:

Acrylics are best known for being durable, inexpensive, and easy to work with. They also provide excellent UV protection and mildew resistance.

As a water-based material, acrylics do not hold up well to ponding water and therefore are not recommended for use on low-slope flat roofs where poor drainage may be an issue.

Additionally, acrylic membranes gradually lose dry film thickness as they age, and colder temperatures can be problematic during their installation.

Click here to learn more about liquid acrylic coatings.

Butyl (Butyl Rubber)

Butyl elastomeric coating is renowned for its exceptionally high elongation and tensile strength. This allows it to accommodate the expansion and contraction (thermal movement) of roof structures.

Butyl rubber is mostly used as a vapor retardant in spray foam applications. It’s also quite popular as a roof repair product.

The primary drawback of this material is its low solids content. This means more liquid material is required during application to reach the desired dry film thickness.

Butyl also tends to discolor over time and can be quite challenging to spray.

Silicone is arguably the most popular type of liquid coating on the market today. It’s a solvent-based material with the highest level of UV stability, flexibility, and resistance to ponding water.

Modern silicone formulations have a high solids content, meaning less liquid material is needed to achieve a certain dry film thickness (DFT).

Silicone roofing membranes accumulate a lot of dirt and dust (usually within 6 months to a year after installation) which can be detrimental to their reflective qualities. Their surfaces are also extremely slippery when moisture is present.

As a solvent-based material, silicone can be difficult on spray equipment, as well.

Click here to learn more about the pros and cons of liquid silicone coatings.

PMMA

PMMA (polymethyl methacrylate) is a liquid acrylic resin that’s best known for its extreme durability and fast curing time.

These liquid roofing systems, which are applied to roof surfaces with a squeegee or roller, are normally reinforced with polyester fleece for added performance. This method of application is more time-consuming and often leads to higher labor costs.

PMMA is solvent-free material with a much broader application window than alternative liquid membrane systems. It’s also highly resistant to ponding water and chemical substances.

Single-component polyurethane is a fast-drying, moisture-cure, liquid roofing material that’s best known for its superior durability, adhesion, and ponding water resistance.

There are two types of polyurethane coating membranes: aliphatic and aromatic.

Aliphatic urethane is white in color and offers better reflectivity. Therefore, it’s typically used as a top coat in liquid membrane roofing systems.

Aromatic urethane has a metallic gray color and is less UV stable, which is why it’s primarily used as a foundational (base) coating. It’s also less expensive than the aliphatic variety.

Polyurethane is a xylene-based material that produces a strong odor which can be bothersome to building occupants.

Urethane coating materials can also be difficult on installation equipment.

Click here to learn more about polyurethane coatings.

Spray polyurethane foam (SPF) is a plural-component roofing material that provides unparalleled thermal resistance (R-value) and waterproofing protection. These systems are incredibly long-lasting, durable, easy to install, and easy to maintain.

Spray foam roofing systems are unique in that they work in conjunction with the elastomeric coating materials mentioned above.

The primary drawback of an SPF roofing system is up-front cost. These systems also have a limited application window and the risk of overspray during installation is a real concern.

Click here for our complete guide to spray foam roofing systems.