Originally Posted by
Brian Hjelm
My son is a civil engineer who is a specialist in concrete and marine structures.
I asked him today about ferro-cement hulls. He says he would not, if he had a choice of anything else. He gives the example of static marine concrete structures where little corrosion and concrete cracking occurs under the tide line. Above the low tide line the porous concrete absorbs salt water and dries out when the tide falls leaving behind salt. Air (oxygen) then enters the capilliaries and corrodes any steel in the structure with the aid of the salt. Rust starts, expands, and starts to break out the concrete. He says concrete is porous having capiliaries and a network of microscopic cracks allowing moisture entry. He says a boat hull will do the same as it is likely to be operated heavy laden and thus soaking the upper level in salt water and then moored unladen thus allowing the water to dry out and corrosion to start same as the static structure. Just takes longer.
He says if one had to built a ferro-cement hull, then an expensive additive should be used. Caltite, which seals the porous passages and is a water repellent. Drawbacks are that it is expensive and the company insists its representatives be present whilst it is being used. If not used properly they withdraw any guarantees and support. He has been involved in a dispute between a property owner, principal contractor, sub-contractors, and Caltite. Caltite techno reps on the site say the concrete trucks were arriving too close together, overwhelming the placing and finishing crews, and finishing was going on after "first set" not to the required Caltite standard.
