Removing ingrained mud from the hull?

[Kelpie]

The new (to us) boat has spent the last four years of her life in a mud berth down in Essex, with only primer on the hull rather than A/F. After arrival up here she was afloat for about three weeks until we got her hauled out the other day.
The hull is covered in a thin but extremely hard layer of mud. Everyone at the yard was actually convinced it was some sort of paint at first. Completely immune to point blank range pressure washer.
I was all set to just A/F over the top of it when I realised that, having had a day to dry out, some patches of it were starting to look a bit crumbly and chalky, and becoming lighter in colour. Sure enough chunks of it came away with the scraper.

I've started removing it but it's a very, very tedious job. Have been at it since 8am and have not even finished one side of the hull. Tried dry sanding, wet sanding, pressure washing, even kitchen cleaner!

Please, please, is there some sort of magic bullet that would dissolve it all away!?

 

[rwoofer]

I have the same hard mud layer and was going to just anti foul over it. I'm all ears if anyone has an answer.

 

[BruceDanforth]

Recruit more people and provide beer.

 

[Kelpie]

Another five hours at it today, using hydrochloric acid and wire wool. Shifted a bit more than yesterday, this stuff is amazing, I think it's some form of clay. Aching fingers and minor chemical burns. More of the same tomorrow!

 

[basil421]

Sounds like the kind of mud we have on the Humber. The only thing that works for me is a draw scraper with a tungston carbide blade like this:
http://www.clasohlson.com/uk/Stiwex-Paint-Scraper/Pr308285000 Still needs a bit of elbow greese but you feel you're making progress

 

[Kelpie]

May have found the answer: heat. When the mud dries out it goes flaky and loses it grip on the paint underneath. I shifted a fair bit using a heat gun today, until the heat gun went up in smoke. Switched to a blowtorch which worked very well until the gas ran out. The end is in sight!!

 

[Daydream believer]

Will it not just chip off with a chipping hammer gently tapped near the worked edge of the mud?
One can actually remove very thick antifoul this way

 

[Durcott]

After a hint from the guy who runs the drying moorings on the River Axe - mud plus poo - I used patio cleaner from 'Proper Job'.

It worked like a dream - very quick, and the hull came up white.

Now - would I recommend you to throw dilute acid on your boat? Not in a million years , but if asked, I would state that it 'worked for me'.

Jeff