Repair of Sprayed Polyurethane Foam Systems
SPF systems are manufactured from a chemically complex mixture of polymeric materials such as liquid isocyanates and liquid polyol resins, which are added to various cell stabilizers, blowing agents, combustion-retarding agents, catalysts and fillers. Polyurethane foam is developed by the heat reaction between the liquid isocyanates and liquid polyol resins coupled with the vaporization of the blowing agent. This reaction forms cells that change the material from a liquid to a cellular mass. The material is spray applied over the existing substrate.
Most problems associated with SPF systems have been from improper application procedures. Preparation of the surface is critical for success. This includes thorough removal of all loose particles of existing systems. Polyurethane will not adhere to dirty, wet or oily surfaces. There is also a tendency on the applicator’s part to over-spray the material in some areas and not provide a constant thickness. Uneven application creates depressions in the surface — or birdbaths — that regularly pond water.
The application is only as good as the applicator. However, since most conventional roofing contractors do not apply these systems, lower paid applicators — with little or no previous roofing experience — are often used. This could explain why roof penetrations such as curbs, drains and vents are often completely covered with the polyurethane foam application.
The spray application is extremely weather sensitive and contributes to application concerns. For best results, the material should not be applied when wind speeds exceed 15 to 20 mph. We have observed that these systems typically perform best in low-humidity climates.
Polyurethane foam is vulnerable to ultraviolet rays and weather degradation. A significant number of SPF failures occur because of the loss or erosion of the polyurethane foam’s protective coating. When the protective coating bond is broken, deterioration can occur from moisture infiltration at openings or splits from expansion and contraction. Even if roof leaks are not occurring, the loss of insulation worsens over time. This condition can occur from aging and natural weathering of the material or excessive water flow. Abrasion can also occur from extensive trafficking or from birds pecking at the foam surface to feed on the insects that migrate into the system. The loss of coating is revealed by the brownish-yellow color of the polyurethane foam.
Repairs to these systems can be completed with SPF materials or other specially manufactured coating materials. To begin, remove the damaged material and thoroughly clean the surface. Trim the exposed foam at the perimeter of the repair area on a beveled 45-degree angle to the depth of the penetration to obtain a clean surface. Splices of 1/8 inch to 1/4 inch are adequate for this procedure. Brush back any loose coating or granules from the surface and abrade any remaining coating.
SPF repair materials are typically provided in a two-component froth pack. Repairs involving removal of the SPF (blisters, ridges, etc.) are completed using the froth pack. The two components — isocyanate and polyol — are mixed together by the repair technician and continuously stirred for 30 to 40 seconds until the mixture shows a noticeable color change. Once mixed, pour the material over the affected area, beginning at the beveled edge and continuing evenly at the bottom of the repair area.
Once applied, the foam will begin to rise and should cure for a minimum of one-half hour. If the material does not adequately fill the opening, additional material can be applied within four to five minutes or as soon as the material is tack free. If the material exceeds the opening, trim away excess foam with a knife or grinder to level of the adjoining roof area.
Once the fill material has properly cured, thoroughly clean the surface and apply the protective coating. The protective coating should be brushed on at a rate of 25 to 30 mils. This application is completed using a two-coat procedure with a minimum four- to six-hour drying time between coats. The same drying time should be used prior to trafficking over the completed repair.
In recent years, a number of manufacturers have developed coatings designed to extend the service life of SPF systems. These types of repairs are surface repairs and do not include removal of the SPF. The coatings are primarily 100-percent-acrylic-elastomer-based coatings that can be applied directly to the polyurethane in all instances except where a silicone coating is applied. Acrylics generally do not adhere to silicone surfaces. One advantage to the use of these products in repair applications is ease of application (no two-component mixing required). In addition, they utilize conventional repair methods and are VOS/VOC-compliant materials.
When completing these repairs, follow the instructions of the coating manufacturer for proper application rates. Steps in this process generally include thorough surface cleaning and abrasion to remove any chalk and repairs to the surface, followed by the application of the new coating. Repairs to the SPF surface are completed with approved adhesives and fabrics.
Although most conventional roofing contractors do not apply SPF systems, there are a number of these existing systems that require annual repair and maintenance. If contractors follow the procedures required to complete these repairs they will make themselves more valuable to building owners and in turn increase their workload and improve the bottom line.