# Gelcoat Mildew-I'm so sick of gelcoat mildew



## bwindrope (Feb 25, 2007)

This is just a rant, and a call for sympathy. 

I'm so damn sick of cleaning black mildew off of every gelcoat surface on the deck of my boat. Sick and tired of it. Here in the PNW, our winters are famously dreary, and are perfect conditions for mildew. My old gelcoat is porous enough to provide great habitat for mildew-I get it. I still don't care. 

Seems my boat is cursed to get the black mold constantly, in all but the warmest summer months. I clean it here, clean it there, scrub it off with my deck brush, scrub it off with a sponge. I get back to a clean white gelcoat, and not a few weeks later it is growing the mold again. 

The mold even grows well on the few painted parts of my deck, where I have Brightside painted. 

I just want to pick my boat up and dip it into a vat of acid and kill all the damn mildew. Kill it. And leave a residue that kills it again and again. 

Yes, I just spent a few hours in the cold and rain yesterday scrubbing mildew off my beloved boat, and would have rather been doing just about anything else on her at the time. 

Damn it. :hothead


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## CalypsoP35 (Jul 24, 2006)

Granted, I'm in the NE, not the PNW, but I have never seen black mildew on a well cleaned and buffed gel coat that is protected by a wax finish. I get mildew on various surfaces (generally below decks) but have never had mildew on my 30+ year old gelcoat. Even when it emerges each spring from under the shrink wrap.


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## bljones (Oct 13, 2008)

I'd feel sorry for you, but my boat is on the hard under snow, for at least another two months. 
i'd rather be scrubbing mildew.


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## pdqaltair (Nov 14, 2008)

Buy dark glasses.

I'm not a Getty, I can't hire a staff to maintain my yacht laugher), and I'm not willing to forgo cruising, sailing, time with my family, skiing, climbing, hiking, cycling... in order to keep up apearances. I wash the boat a few times each year and that's it for mildew treatment. Maintaining Strataglass and mechanical fitness are a different matters.


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## RichH (Jul 10, 2000)

You probably are a victim of 'artillery fungus' a rampant fungus that lives on tree bark and which thrives in cool & wet conditions near forests and woodlands. 

The usual remedy is to keep the gelcoat buffed to a flat surface to lessen the porosity (which holds the moisture) and then fill the remaining porosity with wax, the wax helps shed the water. 

If you don't want to do that, then simply find a clear 'caustic' detergent and spritz/wipe on the surfaces ... the residual caustic on the surface will inactivate the fungal spores. You'll have to wipe on regularly and especially after heavy rain. 

BTW wax is removed by 'caustic' detergents, so you cant do 'both' wax and 'caustic' ... and 'caustics' are extremely harsh on single part paints such as "Brightsides". 
Also check with local 'farm and garden' suppliers as artillery fungus is a major problem with 'home owners' and there are always 'new remedies' for artillery fungus control coming to market all the time.


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## djodenda (Mar 4, 2006)

I've never seen this in Edmonds. My boat turns green, not black.


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## bwindrope (Feb 25, 2007)

Thanks for hearing my rant. I know that waxing would reduce the mold, but really, I am a glutton for boat maintenance and punishment, but waxing the entire cockpit and deck of my Gulf 32 is beyond my limits of absurdity! My main approach is to take a Scotch Brite and with water do a wet rubbing. It takes off a fine layer of gelcoat, and the mold with it, and I know it is just a matter of time before I will have to paint the darn cockpt/decks anyway. 

Artillery mold????? Damn. I just discovered a bunch of orange dots on my deck, is that it? Looks like rust dots, but isn't. Harder to get off than the black mold. Deeper in the gelcoat. 

And yes, I get algae growth too, but not so much. 

Black mold, Orange dots, green slime, what's next?


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## chucklesR (Sep 17, 2007)

Would not a little bleach do the same thing? 
We get spots here (over the winter mainly), whether or not we wax. I pressure spray with a bit of bleach in my sprayer's 'additive' tank. Works just fine, fast too.


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## djodenda (Mar 4, 2006)

This is really weird. I'm not that far from you and I don't get anything like you are describing. I sure wouldn't want to scotchbrite my gelcoat though..

Are you in Eagle Harbor or somewhere else?

Have you tried the Mr. Clean pads?


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## chucklesR (Sep 17, 2007)

Mr. Clean is the equivalent of a 1800 grit sandpaper. Just saying.


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## kellysails (Nov 1, 2008)

I am in Eagle Harbor, wow, the number of green/black decks in our marina is amazing. I think it is due to the large number of Evergreens right on the shoreline. At least that is the theory that I came up with.

Especially on the south side of the harbor.


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## bwindrope (Feb 25, 2007)

Just to be clear, my intent with this post was just to rant and kick up some dust from fellow sufferers, not so much to solicit solutions, though I appreciate those as well. 

I can see using bleach to kill the mold, but it would not remove it right? I mean, the black spots must be gone! I find using a light rub of the scotch brite removes about as much gelcoat as a high grit sandpaper. I happen to prefer Softscrub for most of my hull cleaning needs, as it has bleach and a mild abrasive. I use it especially on the transom for soot and such. 

Anyone else have these orange dots appearing on your boats this winter? It is the first time I have seen them and I'm scratching my head about what they are. They are scattered all over my boat, and there are no obvious solutions other than a growth of some sort. 

And just for fun:

There's a pox on my boat called mildew
And there's very little I can do
To remove the stuff
Without getting gruff
That fungus makes me askew


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## bwindrope (Feb 25, 2007)

Oh, and for location, just this weekend I moved our boat from Bainbridge back up to her normal home in Friday Harbor. Had a great trip with my boys. First night in Port Townsend, and then across the Straits in benign conditions to Friday Harbor. And yes, the mildew seemed way worse here on Bainbridge than up in the San Juans. Go figure.


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## fallard (Nov 30, 2009)

Try this; First you'd kill the nasties with a bleach/soap solution and then buy some Woody Wax and follow the directions on the bottle. I use Collinite wax for the smooth gelcoat, but the Woody Wax treatment on my non skid really works to keep the nooks and crannies relatively clean over the sailing season here in the Northeast.


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## kellysails (Nov 1, 2008)

fallard said:


> Try this; First you'd kill the nasties with a bleach/soap solution and then buy some Woody Wax and follow the directions on the bottle. I use Collinite wax for the smooth gelcoat, but the Woody Wax treatment on my non skid really works to keep the nooks and crannies relatively clean over the sailing season here in the Northeast.


$$$$, yikes!!!!

Amazon.com: Fiberglass & Non-Skid Deck Wax 16 oz. Spray: Sports & Outdoors


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## fallard (Nov 30, 2009)

$53 is a rip off, but if you keep searching on Amazon, you'll find it for about $33--same at Defender. I's about $40 at West Marine. BTW, even at that price I held out for a long time. I finally gave in and--after trying it for 2 seasons--decided it was worth the price.


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## captflood (Jan 1, 2011)

GREETINGS EARTHLINGS :- Try baby bottle sterilizing fluid this has worked for me when other things have failed. It was recommended to a builder by a 96 year old house keeper when trying to cure a mold problem in another house here in UK. AS ALWAYS GO SAFE


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## kellysails (Nov 1, 2008)

captflood said:


> GREETINGS EARTHLINGS :- Try baby bottle sterilizing fluid this has worked for me when other things have failed. It was recommended to a builder by a 96 year old house keeper when trying to cure a mold problem in another house here in UK. AS ALWAYS GO SAFE


OK, that is very original.

Something like this?


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## benesailor (Dec 27, 2012)

I suffer thru something similar. I have barn swallows that use my boat for a habitat when I'm not around which not only stains my deck but helps fertilize the mold. My solution has been to use Soft Scrub with bleach and then apply woody wax. Soft scrub is for fiberglass showers why not boats? It sparkles after that. Much easier to keep clean. I've been using "Nu-finish" on my hull which has been amazing for a fraction of the price. Scrub,buff and apply two coats. "The once a year car wax"; it's recommended for boats. Hopefully it doesn't ruin my gel-coat for future painting down the road. 
I'm going to try a little on the deck this year. I'm concerned that it may make the deck to slippery.


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## benesailor (Dec 27, 2012)

wonder what's in it? hydrogen peroxide?


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## kellysails (Nov 1, 2008)

I wonder also. Looks very safe, it might be the ticket. It seems to be really successful against mold and very very safe. Can't be hydrogen peroxide.

Found a cheaper tablet version, 1 tablet per 5 liters of water. Ships from the UK.

Corp website: Milton | Milton Sterilising Tablets

Tablet version:


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## djodenda (Mar 4, 2006)

chucklesR said:


> Mr. Clean is the equivalent of a 1800 grit sandpaper. Just saying.


Well, that's not good news.. I guess it was too good to be true...


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## OPossumTX (Jul 12, 2011)

Has anyone tried "Wet it and forget it"? < http://wetandforget.com/surfaces_all_wet_and_forget.html >

I have used it on my roof and sidewalks to keep the dark algae and mold off my roof and driveway. It lasts for several months each treatment. Before I found it, I was pressure washing my drive and sidewalks at least twice a year and my light tan colored roof was nearly black. Where I live, between Houston and the Gulf of Mexico, if it is, it molds, gets ball moss, rots or rusts.

I had not thought of using it on Wenonah until I started reading this thread.

On the website (see Link above) it says it is good for boats.

I just read the label and it says not to apply it within 100 ft of any body of water.


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## benesailor (Dec 27, 2012)

in that case just spray some copper sulfate with a pump sprayer. Works on roofs great; why not on a boat?


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## outbound (Dec 3, 2012)

Would think you can wash with vinegar if you are worried about safety then wax. if using liquid wax can add a drop of fungicide into wax ( buy at any paint store) . Personally have used excess teak cleaner or oxalic acid ( woodbleach) to kill mold with fresh water flush immediately after. then dry and wax/bluff with random orbiter. Inside the boat ( lockers/lazerette etc) rub down with vinegar then Arm and Hammer Clean Shower then vinegar again.. Don't have your knowledge base. Only had trouble when boat stored insde. A few sunny days seem to work miracles. Good thing you're not allergic to mold. Must be horrible.


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## Alex W (Nov 1, 2012)

"Wet and Forget" appears to be some sort of a pesticide. Not the kind of thing that I want to be dumping into the local waters. 

I'm reading this thread with interest. My old Catalina 25 has the same problem (it is also in Seattle, on Lake Union), and I still sail on it often since a friend of mine bought it from me. I've never found the perfect solution, but Woody Wax was next on our list of things to try.

It's not a problem in the boat, only on the non-skid surfaces.


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## guitarguy56 (Oct 10, 2012)

Saturday morning I woke up to a sunny day and heard one of my neighbors with the pressure washer cleaning their deck/cockpit... I got the itch so got out the bleach/orange cleaner and a light cleaning pad and got the orange spots and mildew/mold that was starting to take hold and the cockpit is super clean... great but the weather turned cloudy and was not able to complete the deck. 

I'll now have to put on a good coat of wax... thinking something from the auto section I can apply with a cloth without the heavy buffing... what's the best wax for the PNW weather I don't have to buff... wipe on only?


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## bwindrope (Feb 25, 2007)

There is no end of good options for toxic cleaners to kill the mold, both inside and outside of our boats. That's the good news. Inside, my Gulf is a teak palace, and I use lemon oil on the unvarnished teak and find that works well so long as I don't let it go too long. 

No, my problem is really just on the decks. I would go the route of polishing and such, and have done that, but I find that even after a huge amount of work, with all the right products, I get maybe 4-5 months of decent shine and it is back to being powdery. So I'm done with the labor intensive options. 

I like the idea of one of the simple wipe on pore fillers, and if they would leave a more lasting shine and plug the pores to prevent moisture and mold retention, then I am all for it. I have no plans to paint my hull anytime soon, so even if I use a product with polymers or silicone like Nu Finish, I don't care that I would have to strip it deep to paint it, because I have no plans to paint it!


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## Minnewaska (Feb 21, 2010)

If you get to it before it really stains the gelcoat, spray tub and tile cleaner works pretty well. Particularly, those that are bleach based. 

I would buy an electric polisher and get to some serious waxing. All that cleaning does really stink. I can't stand being aboard, if it looks that bad. I bet a good waxing would be less work in the long run. Just don't wash it with anything that will take the wax off.


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## OPossumTX (Jul 12, 2011)

Alex W said:


> "Wet and Forget" appears to be some sort of a pesticide. Not the kind of thing that I want to be dumping into the local waters.
> 
> I'm reading this thread with interest. My old Catalina 25 has the same problem (it is also in Seattle, on Lake Union), and I still sail on it often since a friend of mine bought it from me. I've never found the perfect solution, but Woody Wax was next on our list of things to try.
> 
> It's not a problem in the boat, only on the non-skid surfaces.


I went out and bought some "Wet and Forget" over the weekend. It says on the label something to the effect of not to apply it within 100ft of a stream, lake or other body of water to prevent contamination by run off. Perhaps it would only be suitable to be applied on the hard or on trailer boats away from the water until the stuff drys. I know it worked on my Rubbermaid mail box, composition shingle roof, brick walls, car port and sidewalks all of which are at least several hundred feet from any body of water.

If you rushed out and bought some, I suggest that you read and obey the label to avoid illegal activities concerning the product.


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## pdqaltair (Nov 14, 2008)

The LC50 (lethal concentation) for sunfish is 2.8 ppm for Wet & Forget. Copper sulfate, a worse idea, has an LD 50 as much as 100 times lower than that; unlike bottom paint, it is fully soluable and will wash right in.


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## Alex W (Nov 1, 2012)

OPossumTX said:


> I went out and bought some "Wet and Forget" over the weekend. It says on the label something to the effect of not to apply it within 100ft of a stream, lake or other body of water to prevent contamination by run off.


I think that makes it illegal to use in almost all urban and suburban parts of Western WA, since most storm drains around here drain to the area lakes and Puget Sound.


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## SloopJonB (Jun 6, 2011)

The most powerfully effective "conventional" soap I've used is dishwasher soap. I had to clean the dried on green slime etc. on a van that had been in the weather here for years - it washed off like a regular carwashing when I used the dishwasher soap.

It will strip off any scrap of wax or anything like that though so be prepared to re-wax immediately. It also leave your hands VERY "soapy" so wear plastic gloves or it will take hours to rinse your hands of the slipperiness.

Very cool stuff for those jobs that nothing else will touch.


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## bwindrope (Feb 25, 2007)

I've always wondered about dishwasher soap. You can get versions of that stuff that are eco-friendly and may do a similar job. 

I really appreciate that this thread includes a lot of sensitivity toward the marine life in our waters. I've been around long enough to remember when motor oil was just dumped in the dirt not far from the water in SoCal. When all manner of super toxic chemicals were dumped directly into LA Harbor after hours to avoid paying to have them dealt with (My family were longshoremen and knew these things). 

We've come a long way as a society, and have further to go, and I appreciate that we sailors are increasingly sensitive about the chemicals we use on the vessels we use to explore our magnificent oceans.


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## SloopJonB (Jun 6, 2011)

bwindrope said:


> I've always wondered about dishwasher soap. You can get versions of that stuff that are eco-friendly and may do a similar job.
> 
> I really appreciate that this thread includes a lot of sensitivity toward the marine life in our waters. I've been around long enough to remember when motor oil was just dumped in the dirt not far from the water in SoCal. When all manner of super toxic chemicals were dumped directly into LA Harbor after hours to avoid paying to have them dealt with (My family were longshoremen and knew these things).
> 
> We've come a long way as a society, and have further to go, and I appreciate that we sailors are increasingly sensitive about the chemicals we use on the vessels we use to explore our magnificent oceans.


I watched a documentary on San Francisco Bay recently which had film footage from back in the 50's and even the early 60's where the bay was used by everyone as a dump - people would just back their cars down roads that ended at the water and push everything into the water - old appliances, construction rubble, mattresses, tires - everything. It was astounding that it was that bad in my lifetime.


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## neverknow (Feb 2, 2011)

bwindrope said:


> Anyone else have these orange dots appearing on your boats this winter? It is the first time I have seen them and I'm scratching my head about what they are. They are scattered all over my boat, and there are no obvious solutions other than a growth of some sort.


Are you anywhere near the Boeing plant? Maybe the orange dots are falling off their new aircraft? :laugher


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## bwindrope (Feb 25, 2007)

Ha! That explains it! No joke though, my wife and I used to live in Burlingame, CA, which is just south of SFO and our car and yard would get covered in fine black silt from the airplane exhaust. It was gross. Planes passed just a few thousand feet above us.


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## jworks (Nov 12, 2015)

bwindrope said:


> Thanks for hearing my rant. I know that waxing would reduce the mold, but really, I am a glutton for boat maintenance and punishment, but waxing the entire cockpit and deck of my Gulf 32 is beyond my limits of absurdity! My main approach is to take a Scotch Brite and with water do a wet rubbing. It takes off a fine layer of gelcoat, and the mold with it, and I know it is just a matter of time before I will have to paint the darn cockpt/decks anyway.
> 
> Artillery mold????? Damn. I just discovered a bunch of orange dots on my deck, is that it? Looks like rust dots, but isn't. Harder to get off than the black mold. Deeper in the gelcoat.
> 
> ...


I get the orange spots too. Have you found out what it is ? Tiny dots of it settles at the bottom of the dimples in the nonskid floor. My boat is white. I need help.


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## wfish11 (Mar 27, 2012)

Wash it off, then wipe it down with a weak vinegar solution 1/4 cup per gal of water. Don't rinse it off. That will kill all of the microscopic spores in the surface of the gel coat. It will smell like a salad for a day or two but it will do the job. I bought one of those hose sprayers and every month or so I just hose it down with a little vinegar. Keep it off any fabric, it won't stain but it will fade it eventually.


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## jworks (Nov 12, 2015)

wfis11, I'll try that. Right now I'm testing Dawn, CLR, Tough Stuff, and Pinesol (separately). I've put a drop of each on a "dimple" in the non-skid floor. Letting it sit 15 mins. My hopes on that aren't high. I'll try your vinegar solution if these don't work. I've read elsewhere some people use muriatic acid. They say it won't hurt gel coat if you wash it off immediatey. You can't just wipe something on and rinse off those dimpled floors. Something has got to get down to the bottom of the dimple where the specks are. I have hundreds of them, maybe thousands.


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## fallard (Nov 30, 2009)

jworks said:


> wfis11, I'll try that. Right now I'm testing Dawn, CLR, Tough Stuff, and Pinesol (separately). I've put a drop of each on a "dimple" in the non-skid floor. Letting it sit 15 mins. My hopes on that aren't high. I'll try your vinegar solution if these don't work. I've read elsewhere some people use muriatic acid. They say it won't hurt gel coat if you wash it off immediatey. You can't just wipe something on and rinse off those dimpled floors. Something has got to get down to the bottom of the dimple where the specks are. I have hundreds of them, maybe thousands.


First off, scuffing the gel coat will only make matters worse at it provides a better "foothold" for dirt. That will generate more mildew.

Here's what works for me: 
1. Wash the entire area with a solution of Spray Nine mixed with bleach (1/2 cup of bleach per gallon) and let the wash water sit for at least 5 minutes before a thorough rinse. Keep fabrics away from any splash.
2. While the decks are wet, use Woody Wax, which is applied to a wet deck brush and work it into the porous surface and non-skid areas --using the instructions on the Woody Wax bottle for non-skid. Once it is dry, you blast it with a high pressure garden hose stream and then you towel dry everything.

Caution: Until you dry everything off, things will be slippery, including your non-skid areas.

If you are willing to put a little more effort in the short term to avoid more work in the long term, you might buff the smooth gel coat areas with a light compound and then follow up with a good wax, like Collinite 925, and only use the Woody Wax treatment on the non-skid.

If your gel coat is heavily oxidized, the compounding step is highly recommended for your smooth areas. If the deterioration of your gel coat is such that you can't buff it completely smooth, you could just treat everything as if it were non-skid and use the numbered process above.


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## jworks (Nov 12, 2015)

Fallard, someone on another site recommend Lysol Toilet Bowl Cleaner or The Works Toilet bowl cleaner. I just finished. What took me 3 days last year took 15 minutes today. That was to get the hundreds of orange-ish specks off the nonskid. Yes, I am going to compound the nonskid. Then put the wax on. Thanks.


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## albrazzi (Oct 15, 2014)

chucklesR said:


> Would not a little bleach do the same thing?
> We get spots here (over the winter mainly), whether or not we wax. I pressure spray with a bit of bleach in my sprayer's 'additive' tank. Works just fine, fast too.


I will use bleach as well, usually the Clorox spray and Bleach in the spray bottle. I do know Bleach will remove the invisible oxidizing Stainless needs so if Its even possible keep it off the SS parts of your boat. How about a wash and wax liquid WM has one. I'm with you if its not extremely easy its too much work and cuts into sailing time.


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## jworks (Nov 12, 2015)

I found the answer to my problem. To take the tiny dark orange specks out of my nonskid floor someone suggested Lysol Toilet Bowl Cleaner or The Works Toilet Cleaner. It worked great ! Nothing else I found worked. The specks, whatever they were, settled in the bottom of each dimple in the nonskid floor. All other things I tried would not dissolve them. Not even gasoline. I poured the Lysol Toilet Bowl Cleaner on, spread it around, let it foam up some, and let it sit about 5 minutes. Scrubbed afterwards and rinse it all out the back of the boat with a water hose and they were gone. Success, finally. On one place I let the Lysol sit a bit too long and it left a light blue stain on the white floor. I sprayed some Insta Gone on it and the stain was gone in 10 seconds. Insta Gone is a product that smells like a really strong bleach. Whatever anyone tries to get this stubborn stuff out should be rinsed off immediately with a water hose. Someone I talked to told me it was "pine spores". I don't think pine trees have spores but he may well be right that it was something off the pine trees --- very small and carried by the wind.


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## Minnewaska (Feb 21, 2010)

The problem with virtually all methods of removing mildew with a cleaner, is that same cleaner will remove the wax from your hull (or whatever make be waxed). I try to get this done, before the spring wax, but then can't do so again all season. In some small areas, I will try to clean, then wipe down really well with a wet rag, to remove the cleaner. Otherwise, it just runs off with the next hose and I can see the missing was streaks against the blue hull. They may be less noticeable on white, but removing the wax is still removing a protective layer.


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## SloopJonB (Jun 6, 2011)

No-one mentioned On & Off - I used it for the first time this year on the scum line and mustache on my hull as well as cleaning a bunch of rust stains out of the anchor locker. Also on some other marks & stains of various kinds.

It works amazingly well.


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