Overlap welding
The overlap between the membrane layers should be roughly 51-mm (2-in.) wide to turn it into a 51-mm wide seam. As mentioned earlier, installers should start by spot welding between the two membranes. Once the membrane holds in place with the spot welds, installers should begin applying the welding gun down the full length of the seam. To do this, installers simply insert the welding nozzle under the overlap and heat both surfaces sufficiently to fuse them. While the lap is still hot, installers use a silicone roller to apply sufficient pressure to ensure the two membranes press and fuse together. During this process, installers must be consistent when welding along the lap to obtain a continuous weld (a minimum of 38 mm [1.5 in.]), while at the same time ensuring the welding nozzle remains clean throughout the process. Melted PVC membrane and dust can accumulate on the welding tool; therefore, it is important for installers to remove any debris from the nozzle by using a wire brush.
Butt-welding
Traditional overlap welding works well on the walls and steps of the pool. However, for those installers who want to achieve a superior finish on the pool floor, the use of butt-welding is necessary. The PVC membrane is “butt up” against one another rather than overlapping the material during welding. This welding technique is not always necessary by any means. In fact, many installers do not use this type of weld because a traditional overlap weld is sufficient to obtain a watertight installation. Rather, the use of butt-welding helps improve the esthetics of the pool finish. This technique is more time consuming and, therefore, is only recommended for the floor, which is the most visible part of the pool. The use of butt-welding gives the pool floor an impeccable visual finish. When installers use it in conjunction with a recess cut into the geotextile, this method will give the pool floor a flat finish to provide a smoother surface for bathers to walk on.
For the best butt-welding results, installers should begin by adhering the geotextile membrane to the floor. Then, using a weld-backing strip under the two pieces of the PVC membrane that will “butt up” to one another, they should be welded right in the centre of the head welding band without allowing any space between the two rolls of PVC membrane. When this is done properly, there is no need to use liquid PVC on the seam as the heat of the brass roller will seal the joints together.
