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Old 04 November 2012, 08:57   #1
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Recommendations for Hull Cleaning please

Hi All,
well having searched on this and many other sites I decided to try OXALIC ACID to clean my hull as this seemed to be the most frequently recommended stuff. I have to remove a seasons worth of 'crud' accumulated from being moored up in salt water. My hull has never been moored before and so not anti-fouled, I didn't imagine it would get so 'cruddy' in one summer!
I have used the oxalic acid crystals at the recommended dilution and again at twice the recommended strength, left for 30 minutes then pressure washed with my new Karcher pressure washer at point blank range, and scraped with a large hard plastic scraper, it does not shift it all. I still have a lot of brownish deposits over 90% of the hull, well and truly bonded on. Any suggestions that work would be great!
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Old 04 November 2012, 10:20   #2
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Originally Posted by Wahoo! View Post
Hi All,
well having searched on this and many other sites I decided to try OXALIC ACID to clean my hull as this seemed to be the most frequently recommended stuff. I have to remove a seasons worth of 'crud' accumulated from being moored up in salt water. My hull has never been moored before and so not anti-fouled, I didn't imagine it would get so 'cruddy' in one summer!
I have used the oxalic acid crystals at the recommended dilution and again at twice the recommended strength, left for 30 minutes then pressure washed with my new Karcher pressure washer at point blank range, and scraped with a large hard plastic scraper, it does not shift it all. I still have a lot of brownish deposits over 90% of the hull, well and truly bonded on. Any suggestions that work would be great!
The only stuff I have dealt with is Starbrite hull cleaner although my hull didn't sound anywhere near as bad. Worth a go though.
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Old 04 November 2012, 14:14   #3
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Quote:
Originally Posted by Wahoo! View Post
Hi All,
well having searched on this and many other sites I decided to try OXALIC ACID to clean my hull as this seemed to be the most frequently recommended stuff. I have to remove a seasons worth of 'crud' accumulated from being moored up in salt water. My hull has never been moored before and so not anti-fouled, I didn't imagine it would get so 'cruddy' in one summer!
I have used the oxalic acid crystals at the recommended dilution and again at twice the recommended strength, left for 30 minutes then pressure washed with my new Karcher pressure washer at point blank range, and scraped with a large hard plastic scraper, it does not shift it all. I still have a lot of brownish deposits over 90% of the hull, well and truly bonded on. Any suggestions that work would be great!
Before you use Oxalic acid you must get the rough stuff off the hull - eitehr scraping it or high pressure hose. Then you can use oxalic acid.

Here is the best way and one regularly used by me on a very large yacht to maintain a clean white hull ready for polishing.

Mix up some wallpaper paste to a mixture thick enough that you can use a paintbrush to paint it on the hull with a large paintbrush and it sticks without falling off. Getting the right consistency takes a bit of practice - use less of the wallpaper paste to start. Pour in a reasonable amount of oxalic acid into the mix and stir it. Then paint it on to the hull doing about 2 sq metres at a time. Leave for about 6-10 minutes and then wash off with a hose and sponge. Do not leave it on for more than 10 minutes.

I swear by the stuff and the wallpaper paste trick makes it easier to apply and stay where you want it to. This is basically the same as the more expensive commercial gel product called Y10.
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Old 04 November 2012, 16:30   #4
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Before you use Oxalic acid you must get the rough stuff off the hull - eitehr scraping it or high pressure hose. Then you can use oxalic acid.

Here is the best way and one regularly used by me on a very large yacht to maintain a clean white hull ready for polishing.

Mix up some wallpaper paste to a mixture thick enough that you can use a paintbrush to paint it on the hull with a large paintbrush and it sticks without falling off. Getting the right consistency takes a bit of practice - use less of the wallpaper paste to start. Pour in a reasonable amount of oxalic acid into the mix and stir it. Then paint it on to the hull doing about 2 sq metres at a time. Leave for about 6-10 minutes and then wash off with a hose and sponge. Do not leave it on for more than 10 minutes.

I swear by the stuff and the wallpaper paste trick makes it easier to apply and stay where you want it to. This is basically the same as the more expensive commercial gel product called Y10.
Thanks guys, Nigel, I will try the wallpaper paste next.
I spent around 5 hrs with scraper and power washer to get the worst of it off including seaweed, barnacles, mussels and various other unidentified fauna! As this method didn't shift the stuff closest to the fibrglass I then went online and found various products including 'Starbrite'. Which I believe is basically expensive pre-diluted oxalic acid. Hence I bought 500g of the neat acid crystals to make up my own 'brew'. It did help a bit but as I said, I still have a whole lot to shift.
Does the wallpaper paste do anything to aid the stripping or is it just a way of getting the oxalic on the hull without it dripping everywhere? Can't believe the state I got in as I have to work on it on it's trailer!
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Old 04 November 2012, 17:42   #5
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The wallpaper paste is just to keep the oxalic acid on the hull without dripping on you and off the hull. Wear strong rubber gloves as oxalic acid does burn. Try and use some safety glasses to avoid it splashing in your eyes. Finally if you get in on your hands or face wash with plenty of water.

I know antifoul is expensive but you should never leave a boat on a mooring in salt water or even fresh water for very long without antifouling. One thing about antifouling is that even if one has applied it over many years it is possible to scrape it right back to the gelcoat ready for a new primer coat. However, it is hard work.

As regards a scraper - are you using a scraper designed for scraping hulls as they are much better than a standard paint scraper.
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Old 05 November 2012, 04:54   #6
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Oxalic acid is the thing to use. However, it will only take out dicolouration in the gel-coat, so as mentioned, you need to get the hull pressure cleaned first.

Having done a number of these, I can tell you: -

It will take a p/washer with over 2000psi to easily get the hull really clean.

Mix the acid with the wall paper paste (a good trick) at about 10% acid to water.

There is no need to scrub or scour as the cleaning is done by chemical reaction not abrasion.

Several applications will be needed to heavilly stained areas (be patient).

Once cleaned I would advise you treat the hull with some polish and sealant otherwise you will find that the staining will re-appear quicker and more heavily. Alternatively, anti-foul it!

Alternatively, keep it in a dry stack (sorry couldn't resist).

Steve
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Old 05 November 2012, 06:04   #7
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Hydrochloric acid is also good for dissolving the final brown layer you will be left with.
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Old 05 November 2012, 14:53   #8
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Hydrochloric acid is also good for dissolving the final brown layer you will be left with.
Sounds drastic, would it not damage the gelcoat or tubes? I may try buying from a different source as the oxalic acid I bought was allegedly 95% but didn't seem very aggressive even though my second application was more than double the recommended strength! I had PPE on including goggles and gloves but managed to drip some on my face and wrists as I was lying on my back under the hull (on trailer) most of the time, but never felt any skin irritation or such.

Thanks
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Old 05 November 2012, 15:26   #9
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Just wondering how long you left it out the water before attempting to clean. It is much much easier if done within 24 hours of taking it out of the water. It really depends on where you leave it. Our boat is on a salt water mooring for two months and gets a little bit of weed on the trim tabs and around the transom but that is it. A friend's boat in the marina less than a mile away has barnacles within a month!
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Old 05 November 2012, 15:55   #10
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Originally Posted by Wahoo! View Post
Sounds drastic, would it not damage the gelcoat or tubes? I may try buying from a different source as the oxalic acid I bought was allegedly 95% but didn't seem very aggressive even though my second application was more than double the recommended strength! I had PPE on including goggles and gloves but managed to drip some on my face and wrists as I was lying on my back under the hull (on trailer) most of the time, but never felt any skin irritation or such.

Thanks
Personally as a user of Oxalic acid for many years I would never dream of using Hydrochloric Acid far too dangerous. Oxalic acid is the base chemical in a lot of the commercial cleaning materials liek Y10.

Oxalic acid will sting if you get it on your skin so maybe the stuff you got was not strong enough. Again do mix with wallpaper paste to stop it dripping on you.
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