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Old 27-03-2016, 12:45   #1
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Ferrocement Second Skin

Hi Folks,

Does anybody have any experience on adding a second skin of epoxy mortar to the inside of their ferro? My 54 is being stripped inside, the hull seems generally strong, slightly rusty in places, and some of the internal finish is very rough. She sits way above her lines so I have been toying with the idea of skimming in a 10mm coat - possibly with another layer of mesh?

Alternatively I may just stick with the 6" of mussels that cover the hull below the waterline...

Thanks,

James
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Old 04-04-2016, 23:40   #2
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Re: Ferrocement Second Skin

Below or above the waterline? I just witnessed two cement boats die. One had water intrusion from hollow rebar where water wept in and spider-webbed throughout the entire hull. The other's black iron fuel tank spouted a hole while the owners where away and fuel soaked into the ferro from the inside. They scrapped the boat they'd been on for more than 15 or so years If it had been sealed it would be fine.
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Old 05-04-2016, 00:57   #3
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Re: Ferrocement Second Skin

Epoxy has a different coefficient of expansion so could fail. I'd use Aquron and then paint over.

Aquron CPT-2000
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Old 05-04-2016, 04:23   #4
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Re: Ferrocement Second Skin

Regarding the original question: I understand you consider putting a 2nd layer of mesh on the inside? Is that with concrete/cement?
If so, I would say: don't do that:
- it would be very difficult or impossible for the 2nd coat/layer to adhere to the hull
- the weight gain on a 54 ft boat, ie 15 mt long, 2 metres high, 10 mm thick, x2 for each side, equals approx 0.6 M2 of cement which will weigh around 1500 kg. And some of the weight will be above the waterline.

If you were to use epoxy with glass fillers/matting etc. That will/could work, although it generally is thought that these two materials have different expansion quotients.

I have put epoxy on of deck of my ferro boat 15 years ago, not a problem whatsoever, the thickness varied between 4 and 20 mm, thus hiding the unevenness and wavy deck.
I have used epoxy on other ferro boasts for repair, and every repair remained 100% attached and intact over the years.

Although I never prepared the concrete with acid prior to epoxy application, it seems a good idea though.
However if there is rust and therefore expansion of the steel in the hull or deck, NOTHING will work in my opinion.
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Old 05-04-2016, 06:27   #5
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Re: Ferrocement Second Skin

Thank you for the responses - it all helps me along.

I have seen a second coat of cement added internally a couple of times but am thin on the details. The cement will generally stick well with a a good bonding agent, but the weight is a consideration yes.

Epoxy and mat is the other option which does make a lot of sense to me. I have not come up against the issue of different expansion rates as yet - do you have any other info of this in practice?

As mentioned, the hull does not look that bas, so I am possibly just creating work...
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Old 05-04-2016, 21:22   #6
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Re: Ferrocement Second Skin

Not a ferro boat person but I have seen a number of them patched and the patches stood up well over time so adhesion must not be a problem.


It would appear that if the corrosion of the mesh is not too excessive just getting access, cleaning it up and recoating it would solve any corrosion problem. I would try a pneumatic needle gun to skim of layers to get access.
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Old 06-04-2016, 02:20   #7
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Re: Ferrocement Second Skin

Thanks Raymond - I will remove as much loose cement as possible. I will follow up this post or add some blog pages to help anybody else who gets to this point. The work will begin next month.
Best wishes to all,
James
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Old 27-05-2016, 15:05   #8
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Re: Ferrocement Second Skin

Acid wash first then lots of flushing before applying. (Dry it out of course)
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