Coating Flat Roofs

Coating Flat Roofs

Depending on the type and condition of the roof system, recoating may be an option for extending the life of the roof. Coating costs less than roof replacement, and may provide additional benefits as well. Some benefits obtained from coating a roof can be as follows:

  • Extended roof life
  • Reduced heat gain
  • Aesthetically pleasing
  • Prevent water penetration

Coatings may be applied over a variety of properly prepared roof surfaces. Typically applied over foam, with proper preparation coatings may also be applied over roll roofing products such as modified bitumen, PVC (poly-vinyl chloride), TPO (thermoplastic polyolefin), rubber and others, as well as over shingles and even metal.

 

The Process

The process of recoating generally consists of the following:

  • Sweep and/or blow loose debris off the roof.
  • Patch or otherwise repair damaged areas
  • Pressure wash to remove adhered debris and dirt
  • Prime the roof surface as needed to ensure coating adhesion
  • Apply roof coating – may be more than one coat

Due to the time involved at each step in the process, the typical roof may require as many as five trips to complete.

Foam Roofs

 

Typically foam roofs are restored and maintained with elastomeric acrylic coatings. These coatings contain elastomers (resin) which enable the coating to shrink (with cold) and stretch (with heat) without cracking. They also include titanium to reflect ultra-violet rays from the sun, slowing the rate of deterioration. The primary purpose of elastomeric coatings on foam is to protect the foam from the sun, since ultra-violet rays damage foam.

 

For best durability, white is the preferred color for an elastomeric coating. However, other lighter colors will also perform well. The darker the color (tint) of the coating, the shorter the life span. Accordingly, it is less costly over time to use the lightest color possible as a roof coating.

 

The primary alternative to elastomeric acrylic coatings is silicone.  Silicone has the advantages of acrylics, together with having a longer service life and the benefit of holding up well in ponding water situations.  The downside – the initial investment is higher.

 

Potential Problems

The primary concern with elastomeric coatings is adhesion, or how well the coating sticks to the existing roof system. Adhesion problems are evident when there is sheeting of product, meaning it peels off, or when there is blistering (or bubbles) in the coating. With proper preparation, the chance of adhesion problems is reduced. In cool weather, coatings may not set (dry) as quickly as desired, which can result in cracking due to freezing. Or, rain may come before coatings have set, resulting in coating washing off a roof. In hot weather, the surface of coatings may dry too quickly, sealing moisture underneath, which then causes blistering.

Coatings should be applied only over a clean, dry and solid surface. If moisture is in the existing roof system, coatings will seal that moisture in. Over time, the moisture will rise to the underside of the coating, where it is trapped. With warmth, it will vaporize, resulting in blistering. With cold, it may freeze, forcing the coating to separate from the roof system.