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Author Topic: [Updated]What issues can cause white exterior fiberglass surface to look "moldy"  (Read 465 times)


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What I am seeing on driver side of my 2008 motorhome doesn't appear to be oxidation in as much as the appearance is does not resemble a "hazy" condition as you would expect.  It appears more to be embedded in the actual fiberglass/gel coat where the discoloration resembles what mildew or mold would like on house drywall or siding.  I have a white coach so the pattern of the "grey" blotchiness  stands out.  Its NOT 100% of the driver's side of the coach. There are some areas where it looks as one expects.

The passenger side of the coach all looks just fine.

I have done several different approaches in a small test area with absolutely no change in the condition and I mean NO change at all.
- rubbing compound by hand
- rubbing compound with a polisher
- soft scrub
- barkeepers helper with a scrubbie
- various detergents and cleaners

and power wash.

I am hoping for some way more knowledgeable people could offer a few more ideas.

The problem was indeed mildew.  NOTHING BEATS SUCCESS. The discoloration is some type of mildew embedded in the gelcoat pores. I got 2 heavy cleaners at Lowes this morning, both were recommended as "black streak removers" on a few youtube videos and I got 2 commercial grade mildew and mold cleaners. The black streak removers didn't touch the stuff but the mildew remover did. I may need to make another run to get some more as I got only 16oz bottles to test with. Sprayed on and within a few seconds of wiping off with a damp cloth low and behold, the clean white finish reappeared. I'm thinking the outfit in Arizona that washed and waxed my rig earlier this year had no idea on mildew, afterall, its Arizona....not a good excuse in my book.

Goes down as a "lesson learned".  Now to clean the beast, polish and wax while we still have decent weather here in Illinois to do it.
« Last Edit: October 19, 2017, 08:57:27 AM by decaturbob »
proud to have a 2008 Tioga 31M MH

Rene T

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Re: What issues can cause white exterior fiberglass surface to look "moldy"
« Reply #1 on: October 18, 2017, 05:30:50 PM »
I have the same issue on one end of my shed at my house. It is most likely mold. You need to stop it's growth by washing with a strong mixture of bleach and water.
Rene, Lucille & co-pilot Buddy
AKA  Pep N Mem
2011 Chevy Duramax 2500 HD 4X4
2011 Montana High Country 343RL
From the Granite State of NH
& Florida Snowbird in Lakeland FL


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Re: What issues can cause white exterior fiberglass surface to look "moldy"
« Reply #2 on: October 18, 2017, 05:42:53 PM »
You may want to try white vinegar on it also. Hydrogen peroxide may work as well.
I know you believe you understand what you think I said,
But I am not sure you realize what you heard is not what I meant

2012 Redwood 36RL
2016 Leprechaun 319DS


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Re: What issues can cause white exterior fiberglass surface to look "moldy"
« Reply #3 on: October 18, 2017, 05:57:45 PM »
I always use diluted bleach in a sprayer after it is washed. The results make it look like new. Be careful with the bleach or you can get streaking and other bad results.
Judy & Wayne
2003 Itasca Horizon 36LD
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Retired Electrical Engineer (University of Cincinnati)


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Can you give us the name of the cleaner.  I have the same roblem on my 2004 Brave.


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Zep mildew remover.   A 16oz spray bottle was nearly enough to hand clean one side of my 32ft Class C.
proud to have a 2008 Tioga 31M MH


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Thanks,  I am going to give it a try on my 2004 Brave. It is looking bad and I have had no luck finding something to clean it.