Article reprinted from Western Roofing magazine Sept/Oct 2007.

 

 

Welding

Welding “Aged” TPO Membrane

by Randy Ober, thermoplastics product manager, Carlisle Syntec Inc.

 

 

“How effectively can aged TPO be welded?” This is a question that is posed to me quite regularly. I know it is hard to believe, but not only can I write an unorthodox column for Western Roofing magazine, but I can also actually weld TPO membrane (thus the name Mr. Heat Weld). So this month, I will address the question about welding aged TPO and describe some techniques that have been used successfully to weld older TPO membrane.

                  I had a recent experience with the weldability of aged TPO at one of Carlisle’s TPO manufacturing plants in Senatobia, Mississippi. Yes, the plant is covered with a TPO roofing membrane and it has been in place since 1997. Due to the addition of some equipment in the building, a vent approximately 14” in diameter had been cut through the roof deck, insulation, and roofing membrane. Since I happened to be at the plant, the maintenance staff asked if I could flash the new penetration while I was there. At first I thought that the guys just wanted to see a professional in action but when I got to the roof and recognized that the temperature was 105° outside and I was the only one on the roof, I quickly realized that they had pulled one over on me.

                  In order to make that repair, and any repair to aged TPO for that matter, proper preparation is the most important step in the process. Materials required are plenty of clean white rags, some Scotch Brite® pads, new TPO membrane or flashing, and a solvent-based cleaner. In my example, a proprietary membrane cleaner was utilized but the use of naptha usually also works well. First the surface of the membrane is cleaned using the rags and the solvent-based cleaner. Next, depending on the age of membrane, the Scotch Brite pads are used with the solvent-based cleaner to remove the oxidation associated with the weathering process. The solvent-based cleaner will actually turn the color of the membrane as the oxidization on the surface of the membrane is removed. (Be careful during this cleaning process since a very abrasive pad or a very aggressive individual could actually remove so much material that a poor weld could result). Once the oxidation is removed, clean the surface completely with the rags and additional cleaner and weld with a handheld heat welder. Using this process, the new pipe on the Senatobia facility was successfully flashed into the existing ten-year-old roofing membrane.

                  After what period of time on the rooftop does a membrane require cleaning with a Scotch Brite pad prior to welding? The answer to that question is, “It depends.” The amount of UV exposure (which will vary based on the geographic location of the project), the amount of sunlight (which varies due to the amount of shading from trees or other buildings or the cloud cover associated with the particular area), dirt, and even the type of dirt can all have an effect on the amount and type of cleaning that will be necessary to weld the existing TPO membrane. In sunny Carlisle, Pennsylvania, a study was conducted where samples of TPO were mounted on a southern facing, angled table and exposed to the elements for one year. Every month a sample was removed, wiped clean with a rag saturated with Carlisle’s proprietary solvent-based cleaner and welded. The welded seam was then pulled in a peel mode to confirm a proper weld had resulted. For the entire yearlong test period, in a relatively low UV exposure and low pollutant area like Carlisle, the TPO samples never needed to be prepared with anything more than a wipe by a solvent-saturated rag prior to welding in order to achieve a proper weld.

                  In an extreme situation however, an applicator had issues welding TPO membrane that had been installed for only one day. This applicator had wiped the newly installed membrane with Carlisle’s proprietary, solvent-based cleaner prior to the hot air welding process. After this cleaning procedure, the membrane surface appeared as if it was perfectly clean. When attempting to weld a new, adjoining sheet to the existing membrane, a proper weld could not be achieved regardless of the welder settings. This project was a tear-off and after much discussion, it was determined that the existing roof consisted of coal tar pitch. The direction of the wind was toward the newly installed membrane so contaminants from the coal tar pitch roof tear-off were floating over and being deposited on the new TPO membrane. These contaminants permeated the surface of the TPO and remained a barrier to welding, even after cleaning the membrane with the solvent-based cleaner. Upon utilizing the Scotch Brite pad and the solvent-based cleaner, the membrane welded without incident.

                  In extreme conditions where the membrane cannot be welded regardless of the preparation method, another option exists. The underside of the existing membrane may be cleaned with a solvent-based cleaner and a rag. The new membrane is then slipped under the existing membrane and the topside of the new material is welded to the bottom-side of the existing material. On the ten-year-old Mississippi project that was referenced earlier, the underside of the existing membrane only required a quick wipe with a rag saturated in the solvent-based cleaner to achieve a proper weld. No aggressive or abrasive cleaning was necessary since the underside of the membrane was never exposed to dirt, pollutants, UV, or other contaminants that could alter the welding characteristics of the membrane.

                  Using the methods previously described, existing TPO roofs can be repaired, new penetrations flashed, and tie-in details completed with reliable welds that will perform for the lifetime of the roofing system. •••