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Old 03-01-2013, 12:59   #1
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Ferro-Cement Hull Repairs.

I recently and carelessly parked my ferro boat up on a coral reef in grenada. It was 12 days before we got the right combination of pumps, tow ropes and weather and pulled her off. Now safely out the water I am impressed at her strength though there are some serious repairs to address. There are 3 major holes, the largest about a metre square where I've removed the outer mesh and removed the rubble, then there are a number of small punches, indented about 20mm. A couple of mysteries - there are large areas where she's been grinding on the reef where a kind of orange peel has come away, down to the first layer of weldmesh. It would appear that its like a skim coat thats peeling away though I think it unlikely as the exposed surface under is rough and the mesh is mostly exposed plus its not the proper way to build a ferro hull.
There are unsuprisingly quite a collection of hairline cracks but on chipping seem to only go as deep as this first layer, other cracks low down go right through as bilge water seaps out...
So any tips or advice from anyone whose had experience with this kind of repair, what materials... sika? would be greatly appreciated. I'll try and attach, photos or post a link. Thanks Kieran
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Old 03-01-2013, 13:38   #2
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Re: Ferro-Cement Hull Repairs.

i assume you mean you require assistance on the hairline cracks, many products exist from the major companies to deal with Hairline cracks you will need to look in your area but BASF,Mapie,Bondall and Sika are some in Australia, be carefull to ask and ensure you receive products that will react in salt water as many are made for potable water "domestic tank repairs" and wont work.

Mostly the products to avoid are the ones that require "free limes"to be present to activate the chemical process if the boat is older, many of the available free limes will not be sufficent (these mostly need 150mm of solid poured concrete no older than 10-15 years,but not always.)

You can have a sample of your boat tested to ensure complete compatability with all the products you are using by a concrete testing laboratry.

when you have repaired All the damage some of these companies have cement products that can coat the outside of your hull it is applied as a 3-6mm concrete coating and will waterproof the entire hull , then your antifoul etc can be applied over that (Mapie smart is also flexible, pronto is not).

if you select the correct products and use them as per the details thi will be a fairly simple process but will take time for curing and overcoating

i hope that is of some help
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Old 03-01-2013, 14:27   #3
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Re: Ferro-Cement Hull Repairs.

Sorry to hear of your grounding. Glad you are off and in a work yard.

All the best
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Old 03-01-2013, 14:43   #4
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Re: Ferro-Cement Hull Repairs.

Glad to hear you are off the reef, sounds like your hull is still intact.
Most ferro hulls are made up of approximately 6 mm steel rods about 50 mm apart, forming the shape of the boat, then three layers of chicken mesh are fastened to each side of these rods, inside and outside the boat. A mixture of cement and sand render is then plastered onto the chicken wire, pushed right through, trying to ensure there are no voids, this render is then simply smoothed off inside and out and painted. If the hole is cleanly formed and the rods and chicken mesh are missing from the hole, you may have to break away some of the hardened mortar around the hole to expose some of the existing rods and mesh. (this should be easy to do, hold a heavy hammer inside and a light hammer on the outside to pound the mortar away by crushing it between the hammers all around the hole, maybe 75 mm all around) Tie new rods and mesh to the existing rods and mesh, then plaster the hole to close it. There are wet-to-dry epoxies or bonding agents available for mortar, these can be used at the interface between the old mortar and the new to help with bond and water proofing. A mortar mixture of 1 part GP cement and 1.5 to 2 parts dune sand will be satisfactory to make the mortar. It should only cost a few dollars for materials for the repair. Once the mortar has been applied and has set,(it only takes a few hours) cover the patch with plastic, inside and out to allow the mortar to cure. Cement mortar needs to remain wet for at least a week, preferably longer to cure and gain strength properly. (Strength gain in portland cement is a chemical reaction between cement and water, hydration, if water is lost, the strength-gain hydration process stops)
Good luck on your repairs............stonefloat
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Old 03-01-2013, 23:43   #5
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Re: Ferro-Cement Hull Repairs.

If the hull has lain over on a reef, and probably bounced with surge or tide, she more than likely fractured herself, sometimes horrendously appearing as holes, other places mildly showing as hairline fractures. In either case, she needs redoing or you'll be dancing with the devil from then onwards. Tap with a hammer to hear her ringing. A crisp resound signals sound structure. a thud, or dull retort means broken bonds that should be mended if you desire maintenance free service. Otherwise, cancer may grow. Another way is to sandblast, which eats away unsound areas. I'd be doing that. Amazing what you'll find, and the bonus is you'll be halfway along the repair road. Best of luck.
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Old 08-01-2013, 12:52   #6
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Re: Ferro-Cement Hull Repairs.

Thanks for tips - there does seem to be abit of a mindfield of products but am narrowing it down thanks to advice. I will post what I decide to do and how it works out...
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