b'TECHNICAL & RESEARCH Continued from page 11Figure 13. This machine is a robotic, automatic seam welder gun and a hand welder. Field seams on this project will need be thoroughly probed.Otherfactorsthatwill affectfieldseam-welding qualityaresunlight,wind, shade, ambient temperature, andhumidity.Itisimper-ativethatthedesignatedFigure 14. Comparison of welds. From left to right: poor weld, incomplete weld, and good weld.roboticwelderoperatoris thoroughly trained and familiar with the equipment being used. Roof manufacturers recommend that the subcontrac-tor perform test welds before welding actual field seams.Single-ply membranes Test welds consist of the following steps:1.Set up the welder temperature and speed.2.Perform test welds with scrap material. are flexible and experience 3.Allow the test welds to cool and then attempt to pull them apart in a peel action.dynamic movement during A good weld will be demonstrated by the exposure a solid 1.5- to 2-in.-wide (38- to 50-mm) area of reinforcing scrim, as shown in the scrim on the right side of Fig. 14. Ittheir life spans. As the is important for the designated welder operator to perform these test welds each time they start up the equipmentmembrane around the and after the equipment has achieved the operating tem-perature. The time of day, direct sunlight versus indirect sunlight (shade), high winds, or cloud cover versus sun- scratches expands and shinecanallaffectthetemperature,speed,andoverall weld quality.Hand-welding seams and flashing details are at leastcontracts, the scratches as important as, and often more important than, robotic seam welding. The hand-welding-detail roof technicianscan penetrate through the mustbewelltrainedandexperiencedintheuseofa hand welder. Hand welding requires a great amount of patience and skill. It cannot be rushed, as any attempt atreinforcement and bottom expediting the process can result in poor welds, which can permit moisture intrusion into the roof assembly. Figure 14 provides an example of a poor (cold) weld. A cold weldlayer of membrane.may visually appear to be a good weld/splice, but minimal pressure from a seam probe or wind can cause a cold weld to open and fail.12 www.mrca.orgMidwest Roofer41'