Quick Fixes for Sprayed Polyurethane Roof Systems

01/15/2005 |

Buildings.com - Roofing Newsletter

Several previous columns in this series sought out easy fixes for conventional roofing systems. This month, we’ll look at sprayed polyurethane foam (SPF) and associated coatings.

Repairing Spray Foam
In previous articles, sprayed foam was mentioned as a fix for bituminous and metal roofing systems. Because SPF adheres to just about anything and can be field tapered to build up crickets, it is an important re-cover option.

Now we turn the tables, and look at whether SPF can be easily repaired with either conventional or SPF materials.

Some repairs are really maintenance issues. SPF relies on the protection of surfacing to a far greater extent than bituminous systems. When the opaque surfacing starts to get thin or begins to pinhole, UV light can degrade the foam below. The quick fix in this case is to recoat using the chemical coating identical to the original (silicone on silicone, acrylic on acrylic, or urethane elastomer on urethane).

If the condition of the coating is allowed to degrade to the point where cavitation into the foam is taking place, then a quick fix is no longer an option. Now it will be necessary to scarify both the coating and embrittled veneer of foam down to intact material. This requires an experienced foam applicator that will spray an additional lift of foam, followed by a two-coat new roofing system.

This is no time to call a conventional single-ply or bituminous roofing contractor with no foam experience. It is virtually impossible to remove the applied foam in a neat manner and to get a substrate smooth enough to accept a single-ply or bituminous roof membrane. The foam contractor, on the other hand, understands how to grind away degraded material; then an additional layer of sprayed foam becomes the substrate of choice for a new coating system.

If the SPF roof system is leaking, penetrations of the foam and coating are easy to detect. The foam is closed-cell, so lateral water movement is not a problem. The hole will be directly above the leak, except where water may follow the structural members down-slope for some distance.

These penetrations fall into three classes: punctures from dropped tools or large diameter hail; openings to accommodate new pipes or structural supports; and rupture, such as when a blister in the foam is broken by rooftop traffic.

Punctures are easy to fix, provided that they are reported immediately to the maintenance department. Some building owners have instituted a policy that if the hole is promptly reported, the owners will not back-charge the perpetrator to fix it. But if an outside contractor does the harm and does not report it, the contractor is held responsible for all costs of repair. A typical repair of a small puncture is to use a rag to wipe the hole clean of dust and dirt, and to pump in a compatible caulk. The caulk is buttered onto the surrounding coating for a couple of inches to ensure watertightness.

That holds true for new openings, although the maintenance department is more likely to be aware of these activities since the new openings usually relate to new equipment installations. The problem here is that if the maintenance department is unfamiliar with how to seal the openings as soon as they are made, their improvisation is guaranteed to fail. Bituminous mastics, duct tape, and the like will not work at all. There are two-component foam kits available, which are far more satisfactory. The foam can be used to mold new flashings and to direct water to the drains. Application of compatible coating completes the repair. If the building manager has a good relationship with the original foam contractor, repairs by the professional contractor can be scheduled in advance of opening the roof, avoiding possibilities of weather incidents.

Rupture or delaminating of the foam roof system is a perplexing problem. It usually can be traced back to the original foam application, due to perhaps a damp or dirty substrate or improperly operated spray equipment. In this case, the building manager should first pull up the warranty or guarantee if one exists, and see if there’s a possibility that these problems are covered. If not, or if the warranty has expired, it still is best to go back with a SPF system.

Replacing the system with metal would be expensive, and penetrations through the existing roof system to install structural supports result in lots of holes that must be temporarily sealed against sudden rainstorms. And, there will be issues of fire safety, since the foam is now in an attic setting.

Re-covering with single-ply means perplexing issues with flashings, since SPF is self-flashing. All that foam must be ground away, and the pipes or curbs cleaned and primed to accept flashing membrane or elastomeric boots. The irregular contour of the foam will make it difficult to overlay with a rigid board, common in single-ply re-cover processes. Whether gypsum board or fiberboard is used, and no matter how many mechanical fasteners are used to hold the board down, it will still not result in a smooth and aesthetically pleasing appearance.

How Do We Know What Type of Coating or Caulk To Use?

We mentioned three generic classes of coatings earlier: silicone, polyurethane, and acrylic. If roofing records are not available as to what was installed on the roof, these materials are chemically different and can be identified by any of the coating manufacturers that service the foam industry. Usually, a simple infrared analysis will provide the necessary information, so only a couple of square inches of roof material are needed. To find such coating manufacturers, visit the Spray Polyurethane Foam Alliance (SPFA) website at (www.sprayfoam.com). This site has many useful publications on specifying and using polyurethane foam, as well as a directory of accredited contractors, inspection agencies, and manufacturers.

Quick Fixes?

There is nothing quicker than pumping some caulk into a roof ding. Possibly SPF’s biggest advantage is also its biggest problem: Since the foam does not transmit water readily, the roof could have been degrading for quite a long time before the first leak shows up. By that time, erosion, delamination, and cavitation could be well under way, requiring the scarifying and refoaming mentioned above. The simple solution to this dilemma, of course, is periodic visual inspection, and to budget for re-coating before pinholing becomes widespread. Typically, this is every 7 to 10 years.

If mechanical damage recurs around rooftop units, walkways can be constructed using additional coating thickness and embedded roofing granules.

There have been cases where coatings applied to metal roofs have caused problems. If the coating is not waterproof, or if it has imperfections as a sealing membrane, water can get between the coating and the panel. This accelerates the corrosion of the panel while hiding what is happening. Over time, the panel could rust out since the owner is not able to detect that rust forming.

Helpful Websites:
National Roofing Contractors Association
Spray Polyurethane Foam Alliance

Related Coverage