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Old 19-09-2017, 06:19   #1
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Open mesh on ferro hull

Hi
I am working on 43 ft ferrocement hull that was badly sandblasted years ago and now shows the first laywer of mesh in many areas, some are already rusty.
I want to put on epoxy, what would be the best treatment for the mesh before painting it ? Thanks a lot
Sven
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Old 19-09-2017, 06:22   #2
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Re: Open mesh on ferro hull

Sorry to say but that is beyond reasonable repair IMHO
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Old 19-09-2017, 07:03   #3
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Re: Open mesh on ferro hull

Greetings and welcome aboard the CF, Sven.
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Old 19-09-2017, 07:39   #4
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Re: Open mesh on ferro hull

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Sorry to say but that is beyond reasonable repair IMHO
That is one of the reasons ferrocement boats can not be sold and even giving them away is not easy. In my opinion it is not worth the effort you will need to spend on the repair.
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Old 19-09-2017, 08:12   #5
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Re: Open mesh on ferro hull

Thanks for the welcome Gord !

I really do not think the boat is beyond repair, there are two more FC boats in my marina and they were in worse shape before and now float nicely.

So any good avice from FC-Boat owners out there ?

Thank you !
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Old 19-09-2017, 08:31   #6
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Re: Open mesh on ferro hull

My instinct would be to use epoxy too. Perhaps there is a special epoxy for bonding to cement.
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Old 19-09-2017, 08:39   #7
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Re: Open mesh on ferro hull

Perhaps the type of epoxy that is used on gunite pools??
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Old 19-09-2017, 08:56   #8
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Re: Open mesh on ferro hull

Quote:
Originally Posted by Sven Heiligenst View Post
Hi
I am working on 43 ft ferrocement hull that was badly sandblasted years ago and now shows the first laywer of mesh in many areas, some are already rusty.
I want to put on epoxy, what would be the best treatment for the mesh before painting it ? Thanks a lot
Sven
I am not optimistic however you might put Ospho on the rusted mesh prior whatever you do to encapsulate the hull. Best of luck.
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Old 19-09-2017, 09:34   #9
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Re: Open mesh on ferro hull

You might try first treating the hull with a non-hydrophobic concrete strengthener and sealer. If it's been sandblasted, the concrete is probably pretty porous at this point Then paint the hull with several coats of coal tar epoxy.

I think the suggestion to use whatever they use to waterproof pools and concrete storage tanks is also a good one.
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Old 19-09-2017, 09:46   #10
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Re: Open mesh on ferro hull

There are commercial epoxy based industrial cement floor repair products. They are pretty tough, holding up to forklifts etc. or JB weld maybe .....
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Old 19-09-2017, 09:48   #11
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Re: Open mesh on ferro hull

The type of damage and repair is described in Collin Brook's book ferocement boats.

Because of such results, never sandblast a ferro cement hull. On a good hull you have a very thin layer of conrete over the mesh, just enough to protect it from water. And sandblasting will damage the concret and make the mesh start to rust.

For repair you need to hammer the concrete out, remove the rusted mesh, weld new mesh in, use stringers where needed and use new concrete with an bonding agent, where it meets the old one.

If your whole hull looks like this, then it is like building a new hull. Not economical to repair.

If you leave the rust in, it will keep on destroying the structural integrity of the hull until it fails, hopefully not when you are at sea. You may epoxy before you have rust, to protect the hull, but not after it started without removing the rusted mesh.
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Old 19-09-2017, 09:50   #12
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Re: Open mesh on ferro hull

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Originally Posted by Sven Heiligenst View Post
I want to put on epoxy, what would be the best treatment for the mesh before painting it ?
i think that lightly brushing the exposed wire and then applying a mix of epoxy and microballoons followed by a coat of epoxy would be your best bet. i built a ferrocement boat in my misspent youth, so i know that epoxy sticks well to cement.
all the best
jon
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Old 19-09-2017, 09:57   #13
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Re: Open mesh on ferro hull

Hi FC owner here. I would be very concerned at the extent of rust as well. Just like a dentist remove the cement and rusted wire until you no longer see rust. Retie new screening in (we call it chicken wire) and epoxy just as if you were building it. Also examine the stringers under heads and galley. We found rust there but nothing mortal. We did blast the bottom, but we had done this before on other boats, it takes a very light hand.

This looks like a huge job. Good luck
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Old 19-09-2017, 09:59   #14
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Re: Open mesh on ferro hull

Telling Sven his boat is not worth repairing based on this limited information is irresponsible IMHO. People love to generalize on forums and generally ferrocement boats are not a good investment but if you already own the boat & it's in good shape otherwise scrapping it because of this defect is silly. There are some ferrocement boats out there that are really amazing. Now if this is just the tip of the iceberg & you need to repower, rerig or get new sails then you might want to rethink moving forward. How about some more detail about the boat & some pictures.
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Old 19-09-2017, 10:18   #15
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Re: Open mesh on ferro hull

There's some very sound advice here. Might take a lot of work but she might be able to be saved. Good luck.
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