The mechanism of cobalt spot development
The resins utilized are not 100 per cent impervious to moisture ingression. Many epoxy resins are more moisture resistant. During the fabrication process, microscopic voids in the resin create cavities that water molecules migrate into, together with water soluble materials such as the cobalt promotor. The cobalt in the resin is part of the curing system; it is an activator that is added to the resin which reacts with the catalyst to start the curing reaction. These resins do not cure like epoxies. Free radicals are involved in the curing process with these types of resins. These micro fluids build up pressure in these cavities and eventually burst, spilling their contents on to the surface, which is then oxidized by chlorine. This forms the unsightly purplish cobalt oxide. The cobalt in the resin is the promotor that reacts with the initiator to produce free radicals that start the polymerization process. It is an essential activator for resin curing. Before the use of cobalt, the resin was not room temperature cured and had to be post cured.
The incorporation of bisphenol A (BPA) epoxy vinyl ester resin (EVER) into the fabrication process has all but eliminated the cobalt issue. Today, most reputable pool fabricators utilize EVER in their fabrication schedule as it is more water resistant. The late 1990s also saw the development of new finishes that included “shimmery” looks from the inclusion of thermoplastic particles/flakes in clear resin, which was laid down first before the colour coat and lamination. The initial problem was the haziness of that finish. Today, most fibreglass pool manufacturers offer the shimmer look and solid colours.
Repairing and resurfacing
As the fibreglass pool population has aged, many old pools have come online for refinishing. The most common problems are:
- Cracks in the structure due to movement of the pool or improper setting. Most cracks can be repaired by placing a fibreglass mat first over the cracks.
- Bowed walls. When the pool is not set correctly using faulty techniques, the pressure exerted by dirt puts pressure on the walls causing them to “bow” inwards, leading to bowed walls. One solution would be to cut out the affected area and pump in gunite to create a firm foundation for fibreglass lamination to that area.
- Deterioration of the gel coat finish. All old fibreglass pools show some degree of gel coat deterioration. This can manifest in two ways: thinning of the gel coat that exposes the fibreglass structure and chalkiness.
