Hope this the answer you wanted
When a boat is made of fiberglass (mat and and woven glass fiberes layered up and impregnated with polyester resin), the outer finish is usually composed of polyester resin containing colored pigment. This later is called gelcoat and is sprayed into the mould before laying down the layers of fiberglass matting etc.Because the inner surface of the mould is coated in a wax-based "mould release agent" when the boat is removed from the mould it is colored (by color of the gelcoat) and shiny sort of like a new car. This process makes boats cheaper to make as anyone who has had to have a car (or boat spray painted) will know. However the gelcoat is not as durable as polyurethane paint (which is more flexible and less prone to cracks and weathers better). Gelcoat ages by a sort of plastic rust called chalky oxidation. THe chalk is made of oxidation breakdown products of the polyester gelcoat. Because the long chain polymer chains are broken into smaller and smaller pieces, the eventual process yields chalky material - sort of analogous to surface rust. THis is easily removed by polishing off by an abrasive compound and polish. However some materials (IG Cleansers) can selectively dissolve off the chalk without affecting the gelcoat itself - this is becuase the small molecules of chalk are more soluble that the long chain polymers of polyester of the gelcoat itself.By contrast a non-selective solvent (acetone) will dissolve both chalk and polyester. However, (as for rust on steel) neglected gelcoat also developes down into the gelcoat forming pores or microcrevices that are full of chalk and therefore increasing porosity of the gelcoat. THis chalk absorbs stains (rus, deisel smoke) and makes white gelcoat lose much of its pristine look. On black or dark colored gelcoat, the whitish chalk in the pores also makes it impossible to restore full depth to the color, even with much compounding. In the old days people would then recommend wet sanding down into the gelcoat (hopefully to reach "bottom" of the pores) and then polish and wax. Our IG cleaner conditioners are designed to dissolve out the chalk from deep down and then draw it up to the surface into paper twel soaked in cleanser. As the gelcoat dries back it then draws a clear conditioner down into the pores adding depth. Also the conditioner has anti-oxidants etc and (in case of SEA GLOW) as strong fluorescing agent to "light up" white and bright colors. The final problems that can happen to gelcoat are nicks, scratches and stress scratches. THe latter tend to form around metal fittings due to alternative heat exansion/contraction. They also form (as on my boat) in some areas where the boat has hit the dock a bit hard and the fibreglass hull flexed. Because the gelcoat has no fiberes to re-inforce it is less flexible and may form some surface cracks or crazing. These blemishes are fixed by grinding out the area after first sanding, compounding the area (to get true color) then filling in with color matched gelcoat. In really deep gouges, a polyester or epoxyfiller may be used to help fill to almost the original layer. Gelcoat can be brushed, rollered or sprayed on and a smooth finish formed by covering with plastic film (also prevents surface stickiness) or by sanding/polishing- usually needed in each case. Unlike paint, the suface of fresh sprayed gelcoat will be sticky unless spryaed on the surface with a release agent (similar to that in the mold) or wax can be put in the gelcoat itself. One last thing- although gelcoat is not as tough as two-part polyurethane paint it is easier to apply and much less prone to run and sets up really fast. Two last things, polyester resins (as in gelcoat slowly become more brittle with age andt therfore more porone to stress cracks and then there the matter of osmotic blisters that can form underwater. This is a whole other topic! Hope this is of some help even if rambling! Jim Willis
