By: Kevin Duffy

For the past two monthas we have outlined the advantages and disadvantages of popular roof systems such as single ply and modified bitumen sheet membranes. In this article we will profile a third type of low slope roofing known as liquid or fluid applied roofing. Liquid applied roof membranes consist of a one or two component resin that usually requires a mixed in catalyst.

There are several manufacturers that have developed liquid membranes to be used as stand alone roof systems as well as flashings for their modified bitumen roof systems. Other manufacturers have developed liquid applied roof systems solely as stand alone membranes. There are many advantages to the liquid applied systems. They are aseamlessa, meaning the reinforcement (commonly polyester) fabric is embedded into the liquid and chemically bonded to the adjacent membrane. The seamless look is aesthetically attractive to many building owners and technically attractive to roof experts since the seams are the most susceptible area in any roof system.

One of the most durable of all of the liquid membranes is the polymethylmethacylate (PMMA) membranes. These systems cure relatively quickly and extremely hard. In fact, PMMAas are used in dentistry to fill cavities, and in plastic surgery. Another advantage of the PMMA liquid applied systems is that their chemical bonds allow patches to be easily installed years later, if necessary. The fact that the membrane can flow around any penetration leads to better flashing details than any other roofing system.

The other fluid applied roofing systems that we recommend are polyurethane based systems. These products share many of the same advantages as the PMMA based products, including fast cure time and relative ease of patching. The main difference between the PMMA based products and the polyurethane based systems are the amount of components. Although there are multi component polyurethane based systems, there is the option to use single component membranes. These single component membranes do not have a limit on their pot life, so they tend to be easier to install, often leading to slightly lower prices.

Although these fluid applied systems have many advantages; they do have some disadvantages that must be noted. The one that most often comes up is the price. Their installation is labor intensive and the materials are costly. The products can be very temperature sensitive, which leads to short pot lives and lots of wasted material. Some manufactures offer inhibitors while others separate winter and summer grades of the resin. Until recently, the odor of the liquids also caused many residential buildings to shy away from the products. However, in the past few years, low VOC products have become commercially available. Again, however, they tend to be even more expensive. The difficulty of installation means that hiring the proper contractor, trained and familiar with the particular manufactureras liquid applied system, is essential. Hiring the wrong contractor could lead to early failure of the roof system and voiding of the manufactureras warranty. Another common mistake that many people make is thinking that these materials are a cure all, meaning they can be used over any substrate. Due to the chemicals in many of the liquid applied roof products, they may react with certain substrates such as bituminous materials. These types of substrates will cause the membrane to fail very soon after installation.

As with any big-ticket purchase, it is important to know your options and make an informed decision. The roof systems outlined above and in the preceding articles are meant to give you a basic understanding of the options that are available. In addition to the systems we have discussed, there are numerous other solutions depending on the location, accessibility, and requirements of your building. Stay tuned to Sullivan Engineeringas newsletter for articles on steep sloped roofing solutions.

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