Daveinet wrote:

First of all, it does not work. So for all the naysayers, you are right. Secondly, it does work, so for all the proponents, you are right.

So here is the deal. I just tried to RPM/ZEP my fiberglass Gelcoated boat. It does nothing to effect the oxidation/discoloration. Zero, Zip, nada. It never will. The only way to correct, or get rid of oxidation is by a lot of sanding and buffing. No amount of cleaning or chemicals will have any real effect on the oxidation. The only way to get rid of it, is to sand down to a fresh unoxidized surface. You can pretend all you want, but that's the facts.

So why all the rave reviews? Basically what is happening is that oxidation is primarily white. If you are working with white gelcoat that has oxidized, it has oxidized to the nearly the same color as the original white gelcoat. Therefore, if you coat the surface with something that will make it shiny, what you are actually doing is shining the oxidation. It doesn't cover it, mask it, or change it, it just makes it shiny. So really the end result is that it is difficult to see the difference between shiny fiberglass gelcoat, and shiny oxidized gelcoat, because both surfaces are white and both surfaces are shiny.

So what is the conclusion? If you are working with a white or fairly light colored surface, you can cheat the system and make oxidation shiny. All well and good, and worthwhile. BUT here is the warning. If you are dealing with a dark surface that is oxidized, making the oxidation shiny means that now you have faded, light grey colored ares that are shiny. It does not make those grayish white oxidized areas dark again like the original color. If you have a dark color that has turned light grey, do not waste your time covering it with RMP/ZEP. Because that is exactly what you are doing, you are wasting your time. Not only that, but then you have to strip it all back off again, and then do the actual work of sanding, polishing, and buffing. Once you have sanded all the oxidation off, then it may be worthwhile to put a final coat of RMP/ZEP on it, as the product does shine. But if you are starting with an oxidized dark color, you have to do the hard work.

I just re-did a dark blue boat that was heavily oxidized. I made the mistake of thinking I could play the game, clean it, and coat it with ZEP. I ended up having to strip the ZEP back off, go back and wet sand the surface, and rub it out. When I was all done, I did end up recoating it with ZEP, so the end result looks good, but it took me a lot longer to get there and required a ton of sanding. Hopefully this information will save someone some time. Its not that hard to strip it off when you've discovered it doesn't work on dark colors, but it but it wasted one of my weekends - mainly because I put on about 5 coats, hoping that it would eventually darken up. (like what you see when the surface is wet). Incidentally the top white part of the boat looks good.

I plan to do the motorhome next. Because it is a light color, I believe it will work just fine, without having to do any sanding.

Daveinet wrote:

So if you are going to question my prep, how much cleaning with Bar Keepers Friend do you believe it would take? I started with Bar Keepers Friend doing it by hand. Since it was not making any difference, I switched to the orbital. That still did not make any difference. Basically the Bar Keepers Friend was also pretty much a waste. It may work for soft paint, or to remove chaulkiness, but it really doesn't do much for oxidation. Gelcoat is porous. Oxidation penetrates deep into the gelcoat. Cleaning the surface, or even cutting into the surface slightly with a rubbing compound like Bar Keepers Friend, is not aggressive enough to get through the oxidation and remove it.

BTW: I also tried regular rubbing compound, which is much more aggressive than Bar Keepers Friend. This still would not cut through the oxidation.