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Author Topic:   Cleaning Scum Line - What Works?
BillD posted 08-28-2002 02:51 PM ET (US)   Profile for BillD   Send Email to BillD  
Hi: My 18' 2000 Outrage sits on a mooring in a shallow bay (Shoestring bay, which is part of Popponesset bay in Cotuit on Cape Cod for those that are interested) and gets used on weekends. As a result a yellow scum line has formed about 4 inches wide above the waterline and bottom paint. I know that this is normal to a degree but I am not sure of the best way to clean it. I hauled the boat for a good cleaning last week and regular boat soap, scrub brush and power washer did not touch it. I was hesitant to try anything else for fear of damaging the gel coat, and because it was a beautiful weekend.

What does anyone else use to tackle this problem?

Will waxing help keep it off?

Any advice would be appreciated.

By the way the advice provided in the post in "Post Classics" on cleaning the non-skid was a great help.

Bigshot posted 08-28-2002 03:08 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
MaryKate's On/Off. Orand and white jar about $10. Spray on and watch the scum disappear. Do not ingest because it is acid. Will not hurt gelcoat, nor paint unless you maybe left it on overnight. My boat is imron and I use it.
kingfish posted 08-28-2002 04:22 PM ET (US)     Profile for kingfish  Send Email to kingfish     
Amazing stuff - oxalic, muriatic and a third acid I can't retrieve - does virtually melt the scum away. Read the directions and follow them; wear rubber gloves, and cover your galvanized trailer with plastic. Flushing it with water will not keep On/Off from discoloring the galvanize.


Jimm posted 08-28-2002 05:09 PM ET (US)     Profile for Jimm    
Try this link:

ShrimpBurrito posted 08-28-2002 05:18 PM ET (US)     Profile for ShrimpBurrito  Send Email to ShrimpBurrito     
A liquid product called Ospho does the trick, with phosphoric acid as its main ingredient. Phosphoric acid is also one of very few compounds that will react with, and dissolve, aluminum oxide.

Ospho also works like a charm in removing rust spots from your stainless rails and chrome plated fittings. For this application, as well as removing boat scum, you simply apply, WAIT 10-15 MINUTES (go grab a beer), then come back and it will be gone. You may have to wipe it off with a paper towel, but you definitely shouldn't be scrubbing anything.

I want to say a gallon of the stuff is like $15, plus hazardous materials shipping surcharges.

BillD posted 08-28-2002 05:54 PM ET (US)     Profile for BillD  Send Email to BillD     
Wow - Thanks for the virtually instantaneous response. Now I just need to track down these products in the Boston area, or order them on line. Barkeepers Friend has a nice website so I'll get it there if I can not find it anywhere else.

Where has anyone bought the Mary-Kate's on-off? I can not find even a reference to if in a basic web search, just a lot of pages with those annoying twins.

BillD posted 08-28-2002 06:05 PM ET (US)     Profile for BillD  Send Email to BillD     
Now I found it. The manaufacturers name seems to be "MARIKATE". Thanks again.
Dick posted 08-28-2002 09:17 PM ET (US)     Profile for Dick  Send Email to Dick     
I am a firm believer in MaryKate On & Off but at the marina we use Slimy Grimy for bottom cleaning, great stuff.
Acid based powder concentrate, mix with water and spray on. works very well but I don't think it has a high of acid content as On & Off.
T Party posted 08-28-2002 10:29 PM ET (US)     Profile for T Party    
Liquid Zud, or powder Zud (just don't scrub) - essentially, anything with oxalic acid will work. marikate's on-off has it, Sno-Bowl toilet cleaner has it, but you'd better dilute Sno-Bowl way down.

That's why I like Zud - it has the oxalic acid at a good dilution level.

T Party posted 08-28-2002 10:31 PM ET (US)     Profile for T Party    
oops, I meant to say...
"and it's cheap."
kingfish posted 08-28-2002 10:34 PM ET (US)     Profile for kingfish  Send Email to kingfish     
Phosphoric (see my earlier post)- that's the third acid in On/Off.

Thanks, ShrimpBurrito-


Outraged posted 08-28-2002 11:01 PM ET (US)     Profile for Outraged  Send Email to Outraged     
I've used " The Works" toilet bowl cleaner and a product called "Zing" also does a good job.Gloves are a must with these as well. Outraged
Bigshot posted 08-29-2002 10:50 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I believe CRC makes MaryKate.
Chap posted 08-29-2002 10:56 AM ET (US)     Profile for Chap  Send Email to Chap     
Just used On/Off to clean a summers worth of Toms River, NJ cedar water, bog iron, boat foam stains from my son's Opti. Stay up wind. Perfectly clean, now he needs to rewax it, two coats.
Buckda posted 08-30-2002 02:29 PM ET (US)     Profile for Buckda  Send Email to Buckda     
I've used ZING - works great for all-summer grime....even the thick stuff just drips off the boat...wipe and rinse!
whalerdude posted 09-04-2002 03:08 PM ET (US)     Profile for whalerdude  Send Email to whalerdude     
I like zing

Do not breath this stuff in.

Wear good rubber gloves and eye prot.

It works. It did not hurt the gel coat.

Make sure to not leave it on too long 2 or 3 min tops. then rinse

BillD posted 09-30-2002 02:58 PM ET (US)     Profile for BillD  Send Email to BillD     
I used MaryKate On & Off for the first time this weekend. The stuff is so good it is scary. I can not imagine cleaning the scum line any other way. I ignored the warning to cover my trailer with plastic like the bottle said and got a few drips on the trailer that left black stains even when washed off immediatly. Is this anything to worry about?

Thanks for the advice everyone.

TightPenny posted 09-30-2002 03:41 PM ET (US)     Profile for TightPenny  Send Email to TightPenny     
A gallon of muriatic acid and a spray bottle should cost about $5-6 at a paint store. Good for several years.

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