Today, there are many materials available to choose from, for waterproofing a flat roof.
In the past several years liquid applied membranes proved to be a feasible, economical and more environmentally friendly solution. When searching throughout various roof “coatings”, as these materials are commonly called, roofing contractors realize that not all are created equal.
There are a few general categories of liquid applied membranes for roofing, each of these categories including large varieties of products to choose from. The most frequent fluid products found in both are elastomeric and flexible polyurethane coating, silicone roofing coating, acrylic coating, and many other membranes.
Most of today roof coatings provide the benefits of reflexive white color, which redirect away much of the UV rays and lower the temperature of the roof during direct sun exposure, characteristics known as Cool Roof, but there do have other colors to meet the special demand of certain customers.
Additionally, recovering existing roofs using liquid applied solutions brings the significant environmental aspect of not having to add thousands of tons of scrapped roofing materials every year to the landfills.
Let’s bringing some light over several critical aspects when choosing the appropriate waterproofing solutions for flat (commercial or residential) roofing.
What to do before waterproofing a roof?
A large proportion of the flat roofs covered two or three decades ago with single-ply roofing membranes such as torched-down modified bituminous membranes (mod bit) or with EPDM, are today good candidates for being recovered. Entirely replacing the old roof system with a new one is often prohibitively expensive, but in the past several years liquid applied roof systems emerged on the market as reliable worthy alternatives.
When deciding the most suitable solution for waterproofing a flat roof, the building owner or property manager should take in consideration with equally importance not only the expertise and reliability of the roofing contractor, but as well, the material system chosen.
The first condition that must be met in choosing the right material is the compatibility between the existing roof surface and the liquid product intended to be used. Not paying attention to the type of material previously used to coat single-ply roofs can be a costly mistake. For example, it is a bad idea to apply urethane over a surface previously coated with acrylic elastomeric. The solvent contained by most urethane coating presents a high risk of re-emulsification for the acrylic. Another example, is a roof previously covered with silicone. This type of surface does not accept any other kind of coating, as silicone surface will obstruct the adhesion.
Equally important before waterproofing a flat roof is the proper cleaning of the substrate.
Whether is a new deck or an existing roof system this process is very important, as liquid products need to adhere directly onto the clean bare substrate surface. Debris, grease, dust, or any other bond-breakers caught between the surface of the deck and the newly applied fluid material will weaken or obstruct the adhesion.
Consequently, a substrate not properly cleaned will negatively affect the performance of the cured membrane, leading to its early failure. Pressure washing is the most common method of cleaning an existing roof for the preparation of the surface. Most manufacturers specify for this purpose their own detergent, usually a biodegradable one, or a widely accepted generic equivalent.
Steps to waterproof a roof
A typical application of liquid applied roof membranes consists five main steps, which should all be treated with utmost importance, following the product manufacturer instructions. These steps are: cleaning, priming, treatment of details, main coating application, and inspection.
The first step in waterproofing a roof is cleaning of the substrate. All successful liquid applied membrane applications require superior adhesion. Because of this reason, proper cleaning is just as important as the actual correct application of the liquid material. Typically, pressure washing is the most common method for cleaning the substrate surface. This process eliminates the so-called bond breakers. Additionally, this will expose details needing treatment, that may not be visible at a first glance.
Following cleaning, priming of the surface is designed to improve the adhesion of the membrane. Primers also aid to block bleeding of the bituminous oils from the existing roof through the liquid membrane. Before the application of most primers, the contractors must ensure the surface is dry. To reduce drying time contractors generally use air blower or torches.
The third step is the treatment of details. Contractors must carefully treat all details and only after this step is completed, should they resume the field application of the liquid membrane. Details such as interior and exterior corners, as well as wall to floor type corners, metal flashing terminations and penetrations such as pipes, vents, drains, etc. are typically pre-treated with reinforcing fabric embedded into the liquid membrane and/or with a flashing grade sealant.
These are the most critical points on the roof that can be easily overseen, therefore they demand special consideration. Adequate curing time required by the materials used for details treatment must be followed before applying the main coating.
Next step is the application of the liquid membrane onto the roof. There are two kinds of applications of liquid applied membranes; some require the impregnation of reinforcing mat during installation and some do not. Regardless if the fabric mat is mandatory or not, most of the manufactures require the coating application to be performed in two or more successive layers. The consumption rate of each coating product is stated in the manufacturers’ technical specifications. Method of application, substrate porosity, temperature, and waste are external factors that may influence the specified consumption rate.
In most projects inspection is required by the manufacturer during all phases of the application. This may include, coverage of the primer, pull-out mock-up test, visual inspection of the detail treatments, and nonetheless inspecting the millage of applied coating. Respecting the wet film thickness during application is important. Too much liquid product applied at once will result in uncured material underneath the skinned surface of the membrane. Not enough material to meet the required millage most likely will lead to premature failure of the membrane. Fish-mouths at the edge of the fabric signalize improper coverage of the reinforcement mat at the overlapping section. All such errors must be noted and corrected at the time of the inspection.
Post time: Nov-09-2020