bob26
Well-Known Member
On my halftide mooring in Chichester harbour I get very little weed growth over the season but a lot of sediment which coats the antifouling. By the end of the season this has built up to provide a muddy bottom that is a real chore to scrub off. A pressure hose hardly touches it and until now I have had to scrub it hard (and with triple keels that's no joke as you have to lie underneath it in places).
I mentioned this to an East Coast sailing friend who said he applied hydrochloric acid to his. That sounded a bit extreme to me ...and I wasn't sure how to obtain said acid. But it got me thinking that in all probability the sediment is probably calcareous (chalky) and in my garage I had the remains of a preparation sold to remove chalky/cementy residue from quarry tiles after grouting. According to the label this consists largely of 15-30% phosphoric acid . So I thought I'd try a small test area on my muddy antifouling.
I only meant to do about a square foot but immediately I did so I could see that simply applying it with a paint brush mobilised the sediment so that it washed off easily. I ended up painting the whole hull with a solution diluted 10 parts water to one part of acid before washing off with the power hose. One or two places (where I may not have applied the stuff so well) needed a slight going over with an abrasive pad but otherwise I did not scrub at all and the bottom is the cleanest it has ever been after lift out.
I took what precautions I could (avoiding spray on face and washing hands BEFORE you have a pee!). As far as I can tell phosphoric acid is corrosive but not especially poisonous (its added to cola drinks). And it seems reasonably benign to the environment in dilute form (it actually promotes plant growth). But I'd be glad to hear if anyone knows any good reason I shouldn't be using this stuff. It makes scrubbing off much easier.
And one other thing. Above my boot topping I have a permanent brown stain in the white grp. Where this stuff splashed or overlapped that stain has disappeared. I will probably have to go over it all now as the white splashes and wipes are rather obvious. What's it likely to do to gel coat I wonder?
I mentioned this to an East Coast sailing friend who said he applied hydrochloric acid to his. That sounded a bit extreme to me ...and I wasn't sure how to obtain said acid. But it got me thinking that in all probability the sediment is probably calcareous (chalky) and in my garage I had the remains of a preparation sold to remove chalky/cementy residue from quarry tiles after grouting. According to the label this consists largely of 15-30% phosphoric acid . So I thought I'd try a small test area on my muddy antifouling.
I only meant to do about a square foot but immediately I did so I could see that simply applying it with a paint brush mobilised the sediment so that it washed off easily. I ended up painting the whole hull with a solution diluted 10 parts water to one part of acid before washing off with the power hose. One or two places (where I may not have applied the stuff so well) needed a slight going over with an abrasive pad but otherwise I did not scrub at all and the bottom is the cleanest it has ever been after lift out.
I took what precautions I could (avoiding spray on face and washing hands BEFORE you have a pee!). As far as I can tell phosphoric acid is corrosive but not especially poisonous (its added to cola drinks). And it seems reasonably benign to the environment in dilute form (it actually promotes plant growth). But I'd be glad to hear if anyone knows any good reason I shouldn't be using this stuff. It makes scrubbing off much easier.
And one other thing. Above my boot topping I have a permanent brown stain in the white grp. Where this stuff splashed or overlapped that stain has disappeared. I will probably have to go over it all now as the white splashes and wipes are rather obvious. What's it likely to do to gel coat I wonder?
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