Why Boat and RV Fiberglass Gelcoat Fades by: Bill Rice

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There are probably a million and one temporary band-aid solutions to the problem of appearance restoration and maintenance on faded, dull, chalky. oxidized, discolored or sun weathered boats fiberglass gelcoat or filon panels used in the RV and truck siding markets. Vivilon is not one of those products because our concern is with long term appearance restoration and maintenance. Gelcoat restoration or refurbishment is very similar to paint restoration or rejuvenation in that the objective of both is the restoration of like new, original color and gloss, shine and luster to the gelcoat or paint surface. Taking a dull, chalky, sun weathered, discolored, faded or oxidized surface and restoring it to the color and luster it had when it was new is just a matter of the using the proper  applied chemistry. Read the next  paragraphs and you will learn why fiberglass gelcoat fades or yellows and how to achieve lasting gelcoat or paint restoration on any fiberglass gelcoat surface.

 

Let's be clear, until recently, ALL fiberglass gelcoat was a uniformly poor material to expose to the sun. One leading supplier of polyester resins used in gelcoat said it this way:

"The ability of composite materials to penetrate into business sectors dominated by other construction materials has been limited by a cost-effective means of achieving acceptable performance characteristics with current gel coat technologies. In many cases, the limiting factor has been the gel coats ability to retain its original color and gloss upon continual ultraviolet exposure as compared to the performance of alternate coating technologies."

Now, there are polyester gelcoat resins available that do a better job of protecting color and gloss from the sun's radiation. Some boat builders pay the price to have these better gelcoat materials. Most do not. Read below for more information on why this choice in gelcoat materials is important.

There is only a slight  difference  between the fiberglass gelcoat of boats (and other water craft) and the gelcoat of reinforced polyester fiberglass panels (RFP, sometimes called Reinforced Fiberglass Plastic) Trade named, Filon. Filon is used as exterior siding on almost all fiberglass motorhomes, travel trailer, campers and other RV's. The first difference is in how fiberglass gelcoat is use in the manufacture of boats versus RV's.

A fiberglass gelcoat boat is made with a polished mirror quality mold with is waxed with a mold release agent and into which gelcoat is sprayed. The fiberglass gelcoat polymer used is polyester gelcoat with a styrene diluent to thin the viscosity of the polyester gelcoat and add to the reactivity of the gelcoat blend. The gelcoat is reacted or hardened with methyl ethyl ketone peroxide and let cure.There is one optional step which is taken next by quality fiberglass boat builders. A barrier coat of vinyl ester is sprayed waterline to waterline to prevent osmosis blistering in the fiberglass gelcoat. Possibly, another coat of vinyl ester barrier coat is sprayed in for fiberglass print resistance of the boat. The boat's fiberglass gelcoat will have no imperfections if these steps are taken in the boat building process. Obviously, these extra barrier coats add time and expense to the making of a quality fiberglass gelcoat hull; but, they are worth it.  

The gelcoat color coat is anywhere from 14-25 mils thick without the barrier coat. This compares with a color coat on paint of less than one mil with a clearcoat of

1.5-2 mills for a car. Which brings up the subject of why don't fiberglass boat builders use a clear gelcoat just like auto manufacturers? Unfortunately, the chemistry of polyester gelcoat won't work with a clearcoat like paint clearcoat does. A fiberglass gelcoat boat with a clearcoat will have a haze and develop a yellow appearance to the gelcoat, especially on white or lighter color gelcoats. This problem with clear gelcoat on fiberglass boats is substantially worse than the yellowing problem caused with color gelcoat on boats. The color gelcoat still is visibly effected by the the sun. The sun's UV radiation attacks the aromatic monomer in the polyester gelcoat's molecular structure. An aromatic molecule is notorious for the light sensitivity it has in comparison with more stable aliphatic molecules. Which is why paints used in automotive coatings are ALWAYS aliphatic. For example, the spray in bed liners business popularized by Rhino Linings was infamous for rapid fade of their coatings. This was because of the aromatic urethanes they used. The aromatics were VASTLY cheaper (about a third the price of aliphatic. Because the thickness of the liners, they used a LOT of urethane. The price was right but the performance, as far as sun fading resistance, was wrong.  

Fiberglass gelcoats, for both boats and RV's, start off with this significant double disadvantage over automotive paint. Fiberglass gelcoat manufactures of boats & RV's can't use clear gelcoat and the color gelcoat they use prematurely yellows, particularly on whites, Which is why most fiberglass repair body shops use automotive paints when refinishing a new part on boats and especially on RV gelcoat Filon panels. Recently, polyester gelcoats have been formulated with less aromatic content and with UV absorbers and UV light stabilizers. These gelcoat polymers costs a lot more money. Quality fiberglass boat builders buy them to make their gelcoats perform better in sun light. The other fiberglass boat builders produce cheaper but more sunlight sensitive gelcoats. The saying, you get what you pay for,  applies in fiberglass boat gelcoat like anything else.

After the fiberglass gelcoat is cured, different types and grades of fiberglass is applied to the gelcoat and bonded to give the boat structural integrity. The fiberglass boat is then cured and "popped" out of the boat's mold. The gelcoat that went in first is now the boat's outermost surface. The quality difference between fiberglass boats starts with the kind of gelcoat material they use, whether a barrier or two barrier coats are applied before fiberglass is laid, whether the fiberglass boat is cored and with what, and the time the gelcoat is allowed to cure in the boat's mold.

With Filon panels, manufacture is a continuous process of gelcoat resin(s) being reinforced with fiberglass to produce a panel that has a very shiny and smooth surface on the outside and a somewhat rough inside surface ready for bonding to the frame structure of the RV. Filon is made by Kemlite, which owns the trademark on the fiberglass panels. Their smoothest, shiny, gloss finish is called the Medallion. Extra gelcoat is applied during manufacture to assure maximum gloss. Even though they are basically the only manufacturer of fiberglass panels, and use better gelcoat material with UV light absorbers  and stabilizers, they STILL fade. They admit fiberglass gelcoat panels fade most dramatically during the first few years. Rapid fade is true of ALL gelcoat not just fiberglass Filon panels.

To understand how we restore or rejuvenate a like new color appearance and shine to faded surfaces on fiberglass gelcoat, it is necessary to examine the process by which paint fades, because gelcoat, fades or degrades in the same way. Our article on Why Paints Fade explains the process in some detail. Here we'll explain some further considerations that apply to paint; but, also impact sun fading on fiberglass gelcoat as well.

The first factor that effects the sun's UV radiation ability to impact color retention, luster or gloss on a painted or gelcoat surface, is the gelcoats surface profile. This is simply, when looked at on a microscopic level, how smooth or rough the gelcoat surface is. The rougher it is, the more peaks and valleys there will be in the gelcoat. These peaks and valleys expose more surface to the sun's radiant energy than a smooth surface would. Also, the peaks of the gelcoat are only a few molecules wide, exposing them to more rapid photo-oxidation (sunlight induced damage) than the valleys. And, the valleys provide an excellent place for all types of airborne or waterborne pollutants to collect and further weaken the molecular bonds of the paint or gelcoat.  Of course, compounding, polishing or using a glaze with some abrasive wears down and flattens those peaks and valleys making a smoother gelcoat surface profile. That's one band-aid way to solve that gelcoat problem short term.

The second factor is surface reactivity or how the paint or gelcoat interacts with other materials. Chemically inert (non-reactive) paint or gelcoat surfaces interact far less with the environment and therefore are subject to far slower UV induced degradation of their color, gloss and luster. To put it simply, for either paint or gelcoat, high energy is BAD; low energy is GOOD. The way chemists express this is in the dynes/centimeter number of a surface, or how slick it is. Low numbers are better. Water has a surface tension at room temperature of 73 dynes/centimeter. But, its surface tension goes down dramatically as the temperature rises. The reason HOT water is a much better cleaning solution than cold water is simply that the lower surface tension of hot water allows it to penetrate into and lift grime away better. Adding dishwashing detergent adds surfactants (sur-face act-ive ag-ents) that make it even lower surface tension. Something very slick, like silicone, for instance, is an extremely low 24 dynes/centimeter. And, pure Teflon is 18. For comparison, alkyd enamel, polyester, epoxy or polyurethane is 42-45 dynes/cm. On gelcoat or paint it is vitally important to get the lowest surface tension possible. Guess how low Vivilon takes it?

One measure of this surface reactivity on fiberglass gelcoat or paint, is the paint's or gelcoat's surface energy.  A simple way to express this concept of surface energy is with how water flows over the surface of the paint or gelcoat. A high energy, reactive surface will easily interact with the water molecules and create a sheeting effect. This surface is called hydrophillic because it likes (reacts readily) and easily attracts water molecules. On the other hand, low surface energy paint or gelcoat surfaces are hydrophobic, do not react easily with water and therefore the water beads up. Water is simply an easily understandable way to illustrate the point that low surface energy reduces interaction with ALL the environment's elements especially the worst one, ultraviolet radiation. Another way to say it, is that  if the surface is slick or slippery, it is low energy and non-reactive. That's what you want. Everybody knows this intuitively by their reaction to seeing water beading on a car... It's a good thing!

The third factor (as we mentioned above), is the inclusion of highly efficient UV absorbers and light stabilizers into the paint or gelcoat, which are more fully discussed here.

Now that you have a better understanding of what factors are involved in sun lights UV fading of either paint or fiberglass gelcoats on your boat or RV, you can more critically evaluate what you do for longer term protection of your paint or gelcoat surfaces. For our solution click here.