black spots on the non skid

Ken Cross

Ken Cross

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Oct 24, 2010
2,405
Hunter 30 Everett, WA
I've been doing some cleaning and I have black dots on my textured (non skid) fiberglass decks. I haven't been able to clean it off. It will scrape off easily with a knife, but the non skid surface makes that impossible. So far I've tried boat wash (some kind of detergent), bleach, TlleX, and others with a stiff brush. Nothing seems to touch it. It looks somewhat like mildew.

Any ideas??????
I know someone here has it pegged.

Ken
 
Ron20324

Ron20324

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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
A cleaner won't get it. I have to use a bristle brush. Not the scrub brush, but one that looks like a tooth brush, black wood rectangle-ish handle, the bristles are nylon (SS and brass also avalaible). The bristles have to be small enough to get into the bottom on the non-skid. I actually use that brush on my entire deck. Left and right, then up and down.
 
Terry Cox

Terry Cox

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Dec 25, 2000
5,901
Hunter Passage 42 Shelter Bay, WA
Mildew

Hi Ken, we get the same stuff on our boat. I used to use a bristle brush with a lot of elbow grease to get rid of it. Last year was the first year I used a pressure washer to clean the boat. We have an electric Karcher. Took that stuff right off. We also had that darker swirly mildew (looks like a discoloration in the gelcoat) that scrubbing and washing would not remove. Even the polisher cleaner would not take it off, but the pressure washer cleaned that up as well.
 
Joe

Joe

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Jun 1, 2004
8,161
Catalina 27 Mission Bay, San Diego
To remove biological stains such as mildew and algae, use an acid based cleaner. I have had excellent results with a basic, commercial style toilet bowl cleaner available at any restaurant supply house, such as Smart & Final. It's very inexpensive, a quart will go a long way... I prefer to use a long handled pot scrubbing brush. You can dilute the cleaner in a bucket with a gallon or so of water, dip your brush in and apply, should NOT need much scrubbing... the acid will do most of he work. You should rinse with fresh water immediately afterwards. It'll work.... that's why they "acid wash" swimming pools.
 
Ron20324

Ron20324

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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
Joe said:
To remove biological stains such as mildew and algae, use an acid based cleaner. I have had excellent results with a basic, commercial style toilet bowl cleaner available at any restaurant supply house, such as Smart & Final. It's very inexpensive, a quart will go a long way... ....
Click to expand

Is the S&M caustic, like battery acid?
 
RichH

RichH

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Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
The spots are probably 'artillery fungus' a common fungus that grows on tree bark (especially on tree bark 'compost') in humid/rainy areas; it thrives during cool weather, even in winter.
Such fungals can be dissolved by soaking with a strong alkali/caustic based detergent such as a sodium silicate based detergent as Tuff-E-Nuff, Roll-on; etc.; OR, soaking with TriSodiumPhosphate - TSP or LYE.
To remove the remaining 'shadows' after 'extraction', first rinse with water, then use oxalic acid to bleach the remnants.


These fungals readily 'penetrate' deeply into the porosity of old oxidized gelcoat ( ......... and, can penetrate deeply into the surface of rotomolded polyethylene (kayak hulls, etc.) so deeply that they essentially cant be removed).

The above will totally strip any wax ... so youre going to have to re-wax that entire area to reseal any gelcoat porosity.
 
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G

gfrazzle

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Aug 26, 2007
268
Hunter 41DS Ventura, California
I discovered that a diluted solution of "Spotless Stainless"( a very good product for removing rust from stainless steel) will make removal much easier. Once the nonskid is clean, regular use of easily applied "Woody Wax" will help prevent the stuff from coming back. (I have no interest in either product).
 
Joe

Joe

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Jun 1, 2004
8,161
Catalina 27 Mission Bay, San Diego
Ron20324 said:
Is the S&M caustic, like battery acid?
Click to expand
It's acid based toilet bowl cleaner....... I buy it as Smart & Final 'cause it's cheap. You can buy it anywhere they sell cleaning supplies... under many different brand names... read the content label to make sure it says hydrochloric acid. If there's no Smart & Final nearby go here:

http://www.homedepot.com/p/ZEP-32-oz-Acidic-Toilet-Bowl-Cleaner-ZUATB32/203487312



Is it caustic?... I guess it could be if you don't read the label. But what cleaning product isn't.

Don't know anything about battery acid.

If you're asking me does it hurt the boat... I've used it for many years ... with no ill effects. All the dinghy and beach cat sailors use it to clean the pond scum (algae) from their hulls.

If you're asking me does it hurt the environment....uh.. you're talking about an ounce or so of diluted toilet bowl cleaner... further diluted by gallons of rinse water.... You tell me.
 
lippysyd

lippysyd

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Aug 1, 2012
25
Catalina 27 Curtice, OH
I've had good luck with Tilex Mold & Mildew remover. I had little black specks all over the cockpit that I couldn't get rid of no matter what I tried. Then I tried the Tilex and it worked! The best part is you just spray on, let it sit for about 10 minutes, then rinse. Attached is a pic from my Mom's trailer, which had a much worse version going on.

ForumRunner_20150104_114610.jpg
 
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