and there still might be the odd company who still installs them but it takes a lot of experience and steps do them properly and that is why they have declined in use over the last 2 decades. Having taken a fiberglass course in sailing lessons and then having worked in the old wallace ship yard in deep cove building a Frostad fiberglass fishing boat for one winter when i was younger taught me a lot about fiberglass polyester and epoxy resins.
Fiberglass polyester and epoxy resins are a two part catalyzing process where the resin by itself will remain a liquid untill the catalyst is added at which point you have a limited amount of time to work with the product before it will 'set up'. Putting too little in the mix will cause the product to not cure properly and putting too much in will make it cure too fast before the air bubbles can be worked out of the surface and may cause the finished product to be too brittle and prone to premature cracking even with fiberglass reinforcing mat.
A good fiberglasser will know how much catalyst to add to the resin based on volume, relative humidity, sun exposure and the size of area to be worked on. The first step in applying a fiberglass deck covering is to apply a 'thinned' coat of non-waxed resin to the plywood surface allowing it to soak and lock into the wood so that remaining coats will not delaminate from the wood.
Due to competitive disadvantages this first step is often bypassed and the fiberglass mat is placed directly onto the plywood and resin is poured overtop where it is impossible to tell whether or not the resin soaked through the mat far enough into the wood to bond consistently to the plywood substrate before the resin 'sets up'. The single layer of reinforcing fiberglass mat should be a weight of 1.5 oz but over the years has been reduced to 1 oz mat in order to be competitive in this labour intensive installation like all other two part catalyzing products.
Once the first resin coat is applied air bubbles trapped in the mat will need to be rolled out with an aluminum finned roller before the product cures otherwise bubbling and delamination can occur. Before the last resin coat is applied a non-skid texture will need to be added to the mix that in the old days used to be crushed walnut shells but silica granulars have been used since their inception.
The final step is adding the color often referred to as Gelcoat that is a waxed resin for a smoother cleanable finish that again uses catalyst. Gelcoat can be bought as pre colored resin or color pigments can be purchased and mixed together with a waxed resin to create your own colors or to match existing surface colors to be repaired.
Repairing fiberglass sundecks may eventually leed to more noticeable repairs and more money and the inevitable fiberglass deck covering service life replacement including the plywood depending on what decking product you would like to replace it with. Fiberglass deck repairs will involve removing the bubbled or cracked area by grinding and parging and allowing time for any moisture from leaks to disapate.
Reinforcing fiberglass mat should be used with repairs because without it the resin will crack. At this point the client will have to decide wether or not they will procede with trying to color match the exisiting patch with the faded gelcoat or scuff grind the entire deck down to remove resin waxes and environmental contaminants and recoat the entire surface for a new look however new delamination bubbles could appear again as the fiberglass seperates from the plywood in other areas as the fiberglass deck reaches it's final service life.
Putting vinyl decking over an existing fiberglass deck can be done but requires extra surface preperation. Any delamination bubbles need to be removed and filled and there is no guarantee that the fiberglass membrane won't bubble in another spot later on after the vinyl is applied overtop of the fiberglass decking.