Roof Coatings
During the middle of the 19th Century, a new type of roofing was created by soaking rag felt in tar (pine tar or coal tar) and layering these felts with moppings of hot tar and covering the assembly with gravel. The tar was eventually (mostly) replaced by asphalt, and the rag felt with fiberglass mat to create the modern Built-Up Roof (BUR). For the better part of a century, if a low-slope roof was called for, the hot-applied Built-Up Roof was the only choice. In the middle part of the 20th century, as roof coatings became more popular, someone discovered that cold-applied roof coatings could be used to adhere the plies of roofing felt, and the use of hot asphalt and roofing kettles could be avoided. The first cold-applied membrane roofing system was invented.
Roofing technology has evolved rapidly since then, and there are dozens of different materials that can be used to create a roof today. Cold applied roofing systems have advanced in step and are more popular today than ever.
Types of Cold-Applied Roofing Systems
The term "cold applied roofing system" is traditionally taken to mean a built-up roofing system assembled using solvent-borne bituminous (liquid) adhesives and multiple plies of reinforcement. There are, however, several other types of roof membrane systems that do not require heating are now on the market (single-ply, spray foam, etc.) so it is necessary to be more specific. RCMA members manufacture the following specific types of cold-applied roofing.
Product Advantages
The primary advantages of roof coatings and cements are their economical, proven performance life, and ease of use. Roof coatings and cements are generally one-component products that can be applied directly from the container. Todayís coating and cements are versatile and applicator friendly. Non-flammable products are also available.
1. Cold-Process Built-Up Roofing System
This type of roof can now be constructed a variety of ways. The predominant technique is to use heavyweight asphalt coating fiberglass "base" sheets and adhere them with solvent-borne asphalt adhesives in multiple plies. The first sheet is usually mechanically attached to the substrate (insulation) and subsequent plies (usually three or four total) are embedded in an application of adhesive at a rate typically between 1.5 and 2.5 gallons per square (100sq. ft.) The membrane is then covered with an aggregate surface or roof coating.
Cold process built-up roofing systems now exist that use coated or uncoated polyester reinforcements, or composite (polyester/fiberglass) reinforcements, in conjunction with either solvent-borne or waterborne adhesives. The combination of reinforcement and adhesive is typically proprietary to the system provider and compatibility should be verified with the manufacturer.
Cold process built-up roofing systems are available as complete systems or as repair system for new construction or re-roofing, and they are available in a variety of constructions to meet all budgets. Roof rated by Underwriters Laboratories (UL) and Factory Mutual (FM) are now available.
2. Adhesive Application of Modified Bitumen
Membranes Modified Bitumen roofing is similar to built-up roofing in that it employs reinforcing materials coated with bitumen. The primary difference is the use of "modification" or addition of polymers to the bitumen to achieve improved characteristics. Like built-up roofing, modified bitumen roofs were typically installed using moppings of hot asphalt. An alternate approach for some types of modified bitumen was to use a propane torch to melt the back of the sheet, creating a molten adhesive in which the roll could be embedded.
Perhaps the fastest growing segment of cold-process roofing is the application of modified bitumen roofing in bituminous cold-process adhesives. For obvious safety reasons, use of cold-applied roofing has provided an attractive alternative to the use of hot asphalt or open flame. These roofs typically have a mechanically attached base sheet, and one or two plies of modified bitumen membrane installed in bituminous adhesives.
3. Liquid-Applied Monolithic Membrane Systems
A third type of cold-applied roof now exists which blurs the line between roof coating and roof membrane system. That is the liquid-applied monolithic roof system. Typically made of high-tech polymeric resins such as urethanes, or bitumens which have been modified with polymers such as SEBS, these roof are applied as a liquid and may not rely on reinforcing material, but cure to form a tough, rubber-like membrane. These types of roof are monolithic (no seams) and are typically considered self-flashing.
Roof coatings, in all their various forms -- bituminous [asphalt or coal-tar] and non-bituminous [acrylic or elastomeric]; brush, spray or trowel grade; petroleum solvent or water thinned; furnished in cans, pails, drums or tank wagons -- are all quality products that are easy to use and economical.