Restoring Fiberglass RV Siding
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Most RV siding is a very thin fiberglass skin attached to plywood backing. The very outermost surface of the fiberglass skin is called "gelcoat" which is porous and subject to oxidation. Keeping gelcoat in top condition requires different steps as compared to modern urethane automotive finishes. Fiberglass boats have a gelcoat finish similar RV's, however the gelcoat on an RV is almost paper thin compared to a typical boat.
On an RV the gelcoat finish is relatively smooth and shiny, however it is so thin you can actually see the fibers just below the surface. With the passage of time, the unprotected gelcoat will oxidize and eventually take on a chalky appearance. As it ages it becomes more porous and will fade, weaken, and stain faster and more severe. This process continues until the siding becomes dull and weatherworn. The good news is that many times the gelcoat finish on fiberglass RV siding can be restored.
Step 1 is a thorough cleaning to remove surface dirt and road grime. Wash the RV (see washing article) with a detergent that emulsifies the contaminants and lifts them away from the fiberglass surface. This reduces the amount of aggressive scrubbing required since aggressive use of a brush or sponge on a dirty surface can actually cause damage. After washing and drying a soft wipe down with automotive wax and grease remover should strip and remaining wax or sealant.
Step 2 is spot cleaning to remove deep stains. Black streaks are a common problem and usually caused by mold or mildew forming on the porous surface of unprotected gel coat. The black streak remover goes after organic matter stains. If the gelcoat has been left unprotected for a long time, the surface probably has become porous and stains might be deep seated and impossible to fully remove.
Step 3 is removing surface oxidation to restore the shine. Light oxidation manifests itself as a slight dulling of the gelcoat. Moderate to heavy oxidation can be seen in gelcoat that has a chalk-like powder at the surface. This step is achieved by using Rubbing and/or Polishing Compounds that are basically a form of liquid sandpaper. This can be done by hand or with a machine.
Rubbing Compound is more aggressive than Polishing Compound. We found 3M Super Duty Rubbing Compound works well on the heavily oxidized surfaces. However these abrasive pastes remove some of the gelcoat with each pass so care must be used. 3M Marine Finesse-It polishing compound can be used to further refine the quality of the surface gloss. A hand held electric buffer/polisher can help speed the process.
Step 4 is protecting the surface and the shine you achieved through the previous steps. After polishing, wipe down the coach with clean microfiber towels. Spraying the surface with a light distilled water mist will help remove any remainder of compound. Now it is time to wax or seal. The wax protects the polished surface by filling the porosity and sealing out oxygen, and reduces the effects of damaging UV light. Of course, wax does not last forever, so periodic washing and waxing should help keep the coach shiny and new without having to always repeat Steps 2 & 3.
Modern polymer sealants are typically considered superior to waxing as the provided a protective shield over the gelcoat through a chemical bonding process.
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