Q: Can geomembrane welding be done below freezing (32 degrees Fahrenheit [0 degree Celsius])? If it can be done, is there a method or preferred procedure to assure its success?
A: If the soil beneath the geomembrane is frozen, the heat from the welders may thaw moisture from the subgrade and allow water to condense on the underside of the geomembrane before the seam is welded. This possibility may be eliminated using suitable seaming boards or slip sheets pulled in advance of the seaming activity. For sheet temperatures below 40°F (4°C), shielding, preheating, a slower seaming rate, etc., may be required. These techniques are summarized in GRI-GM9, Practice for Cold Weather Seaming of Geomembranes. The practice also outlines more frequent seam testing and other precautions to ensure quality in cold weather. In all cases, a sharp and frozen subgrade must be avoided so that stress concentration on the geomembrane can be negated.
Please note that the above commentary and information contained within the GRI-GM9 practice does not supersede the directions of the project engineer and the formal plans and specifications. In most cases, a formal written exemption needs to be obtained before such work can commence in cold weather. This is much more complicated than modulating the pressure, speed and temperature of the wedge welder. In all cases, a specific seaming window tailored for the geomembrane type at hand and contingent on changing environmental conditions is needed. All this is checked with increased frequency prior to startup and destructive seam testing by on-site Certified Quality Auditor (CQA) personnel.