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Thread: Cement and re-bar ballast casting

  1. #36
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by 62816inBerlin View Post
    This would tend to indicate that steel punching scrap is not a good idea, it seems to rust from the cut edges inwards. Rebar is probably better as the bars have an intact rolling surface, but you'll still have to use the optimum concrete mixture and inspect the keel regularly.
    How old was the boat? Your point about cut edges is a good point, and one might have thought if they were thoroughly coated and sealed in resin, there should not be a problem.....at least short term. Plenty of old boats with encapsulated steel/iron ballast have had issues.
    If i could have got the slab of bridge grade steel i was after, it would be a one fit and forget, as it stands, the money i saved from going ferro-cement was enough to pay for a new propellor shaft and tube.

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    Default Re: Cement and re-bar ballast casting

    Normal building construction along the coast where i live is 2" minimum concrete over rebar to keep it from busting later. The most experienced contractors go 4"on ocean front building. Less than 2" and problems are likely. I would coat your concrete with epoxy to help seal it from wetting the wood. I don't know anyone who has done that but one of my previous carvel boats had concrete and the frames rotted around the top edge of the concrete while planks remained aok. The iron burried in the concrete showed no issues either. I've seen a few like this. Last month I removed 180 lbs of steel pellets from a fiberglass boat keel. The pellets were glassed over with an approx 1/4" skin on top. Not sure how it got there but enough moisture got in to explode the pellets and fracture the 1/2" fiberglass outer skin. It busted out a chunk of skin about 6" x 12".

  3. #38
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    Default Re: Cement and re-bar ballast casting

    I have some epoxy coal tar that would be ideal as a surface treatment, or i might just glass the topside face and the bottom of the floor/keel face mating surface before bolting it up on tar or something non-stick. I can wait until next summer when it will be bone dry, and sheath the entire casting,should i think it needed, until the casting is turned over,i wont know 100% that the cement did run under everything that it should have, and its only a 4mm skin over/under the bars. I have a heap of cloth i can use to armour the base of the entire box, virtually encapsulating the casting. Time will tell.....

  4. #39
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    Default Re: Cement and re-bar ballast casting

    Length of railway line might be a good reinforcement as well as being heavy.
    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Cement and re-bar ballast casting

    Where does one get railway track? I'm guessing picking a a piece from an active railway might be viewed dimly by those blokes in uniform.

  6. #41
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    Default Re: Cement and re-bar ballast casting

    It's a bit late, but I don't think anyone else has mentioned this so I will. Perhaps this will be useful to anyone considering reinforced concrete ballast.

    You can get hot dipped galvy re-bar. Once it's cut you can dip the ends in melted zinc to protect them.

    I'd have provided more lateral support by alternating longitudinal and transverse layers. I'd also have included fiber in the mix.

    https://en.wikipedia.org/wiki/Fiber-reinforced_concrete

    Polypropylene and nylon fibers can:

    • Improve mix cohesion, improving pumpability over long distances
    • Improve freeze-thaw resistance
    • Improve resistance to explosive spalling in case of a severe fire
    • Improve impact– and abrasion–resistance
    • Increase resistance to plastic shrinkage during curing
    • Improve structural strength
    • Reduce steel reinforcement requirements
    • Improve ductility
    • Reduce crack widths and control the crack widths tightly, thus improving durability



    I studied up on ferrocement boat building once and distinctly remember that it was recommended that the mix contain some sort of tin compound to prevent corrosion.
    Last edited by Gib Etheridge; 09-15-2018 at 11:14 PM.

  7. #42
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by Gib Etheridge View Post
    It's a bit late, but I don't think anyone else has mentioned this so I will. Perhaps this will be useful to anyone considering reinforced concrete ballast.

    You can get hot dipped galvy re-bar. Once it's cut you can dip the ends in melted zinc to protect them.

    I'd have provided more lateral support by alternating longitudinal and transverse layers. I'd also have included fiber in the mix.

    https://en.wikipedia.org/wiki/Fiber-reinforced_concrete

    Polypropylene and nylon fibers can:

    • Improve mix cohesion, improving pumpability over long distances
    • Improve freeze-thaw resistance
    • Improve resistance to explosive spalling in case of a severe fire
    • Improve impact– and abrasion–resistance
    • Increase resistance to plastic shrinkage during curing
    • Improve structural strength
    • Reduce steel reinforcement requirements
    • Improve ductility
    • Reduce crack widths and control the crack widths tightly, thus improving durability



    I studied up on ferrocement boat building once and distinctly remember that it was recommended that the mix contain some sort of tin compound to prevent corrosion.
    An informative post. One of the reasons for allowing steel to weather, especially if using gal mesh wire, was to allow the zinc to weather, as fresh zinc will react with concrete, gassing off hydrogen that can impair the bond.
    The modern additives, polymer fibres are something i would definately look into on a bigger project.
    I believe some guy in Australia built a ferro boat using a completely stainless steel armature, and despite its resistance to rust, many wondered about its long term life being deprived off oxygen.....i wonder how it worked out? Yes you can shot blast and epoxy prime the steel work before the pour and maybe a good idea if it was permenent ballast; but it my case, this is most likely a short term substitute, i know at some point down the line it will "blow", but by the time that happens, i will know more about what the boat might need in the way of fixed ballast and where. Im still experimenting, hence why i thought twice about posting.
    Its hard to get anything "scrap" here, due to strict re-cyling and enviromental rules, so no used tyre weights which are no longer lead anyway due to health hazard, and no railway line!

  8. #43
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    Default Re: Cement and re-bar ballast casting

    I'm betting there will be no corrosion issue at all, but even if there was, surely it would take a very long time before serious problems arose? How long does a boat need to last?

  9. #44
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by Small boats rock View Post
    I'm betting there will be no corrosion issue at all, but even if there was, surely it would take a very long time before serious problems arose? How long does a boat need to last?
    According to some people here, if its not built from materials and to a standard to pass on to your great great grandchildren, then why start? For 4 hours work and the cost involved, it would not be an issue if it had to be replaced every 5 years. The boat has to last as long as i wish to use it, that might be another 10 to 20 years, after that, what does it matter? Im not building an heirloom.......

  10. #45
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by Small boats rock View Post
    Where does one get railway track? I'm guessing picking a a piece from an active railway might be viewed dimly by those blokes in uniform.
    Any of the big metal recyclers here, Wanless, Simsmetal.
    '' You ain't gonna learn what you don't want to know. ''
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  11. #46
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    Default Re: Cement and re-bar ballast casting

    Agreed. Very much look forward to seeing how your build takes shape.

  12. #47
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by PeterSibley View Post
    Any of the big metal recyclers here, Wanless, Simsmetal.
    I didn't know. Thanks for the intel, I reckon some track would have plenty of good uses.

  13. #48
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    Default Re: Cement and re-bar ballast casting

    They don't always have it, but often.
    '' You ain't gonna learn what you don't want to know. ''
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    Default Re: Cement and re-bar ballast casting

    Skaraborgcraft, please don't get angry at people merely trying to help. If you choose not to accept the offered advice, it does not make you wrong; you are free to go your own way and make decisions as you see fit. I, for one, will not get upset if you disregard what I suggest. I will only become strident when I perceive that you are about to make a decision that, in my opinion, might put you or others at physical risk. Even then, I will state my case as clearly as I can only once, then withdraw.

    I will admit that it is this sort of situation that makes me cautious about offering what advice I can to this forum. What starts out as a gentle suggestion turns into a flood of unsolicited advice and ends up with everyone involved unhappy about the situation. It is a shame, because we are supposed to come here in a spirit of friendly mutual support in the pursuit of the building, care, and use of the wooden boats we profess to love.
    Hope for the best, but plan for the worst.

  15. #50
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    Default Re: Cement and re-bar ballast casting

    MMD, no upset here Michael. My response clearly stated you have a valid point. As you can see from the various posts, there is more than one way to skin a cat. Im just showing the way i am doing it, and its not to say it is correct for anyone but me, and for the purpose it will be used for. Sharing is what its all about and your comment holds weight. I am happy with what choices i have made, and that is all that matters at the end of the day, that is not to say alternate views are invalid or not worthy of discussion. I feel as though i have explained its purpose and why i have gone down this route. Im laughing, but this is exactly why i had second thoughts of starting this thread, but maybe it might be of interest to someone else further down the line, which is why everyone elses comments and opinions are welcome.
    And without trying to come across as a "know-it-all", i had already decided how this was going to be done from the outset, i was not asking for any guidance, but again, other views and experience sharing are welcome. I take sole responsibilty for my actions and choices. Dont sweat it, and thanks for posting, your views are always welcome, even if i should not choose to do what you might do yourself.

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    Default Re: Cement and re-bar ballast casting

    That's the beauty of this place, we all can and do learn from the experience of others. It's like a free injection of knowledge. Who wouldn't want that?

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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by skaraborgcraft View Post
    According to some people here, if its not built from materials and to a standard to pass on to your great great grandchildren, then why start? For 4 hours work and the cost involved, it would not be an issue if it had to be replaced every 5 years. The boat has to last as long as i wish to use it, that might be another 10 to 20 years, after that, what does it matter? Im not building an heirloom.......

    Quote Originally Posted by Gib Etheridge View Post
    That's the beauty of this place, we all can and do learn from the experience of others. It's like a free injection of knowledge. Who wouldn't want that?
    Sometimes the well intended and valuable 'help' is not aimed at the OP, but at the hundreds of readers who are looking for advice for similar applications.

    So, not for the OP who does not need my advice. -- A layer or two of heavy gauge wire fence might have been a good idea. As for galvanized: https://galvanizeit.org/education-an...y-coated-rebar
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  18. #53
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by mmd View Post
    Skaraborgcraft, please don't get angry at people merely trying to help. If you choose not to accept the offered advice, it does not make you wrong; you are free to go your own way and make decisions as you see fit. I, for one, will not get upset if you disregard what I suggest. I will only become strident when I perceive that you are about to make a decision that, in my opinion, might put you or others at physical risk. Even then, I will state my case as clearly as I can only once, then withdraw.

    I will admit that it is this sort of situation that makes me cautious about offering what advice I can to this forum. What starts out as a gentle suggestion turns into a flood of unsolicited advice and ends up with everyone involved unhappy about the situation. It is a shame, because we are supposed to come here in a spirit of friendly mutual support in the pursuit of the building, care, and use of the wooden boats we profess to love.
    Hmm, I didnt see anyone get anywhere near angry on this thread. Indeed it's been one of the most civilised threads concerning a process that someone like like Cleek would have dismissed as batshyt crazy that I've seen for a long time. The whole thread has read as an open exchange of ideas on a process which is a bit left of field. As though this was a well regulated discussion group with strict protocols about being polite and respectful and encouraging members to exchange different ideas with out dismissing the contributions of others with contrary points of view. If only more of our threads progressed this way.

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    Default Re: Cement and re-bar ballast casting

    Skaraborgcraft, thank you for sharing this. I have often wondered about concrete for ballast. (It's a ready available material for me since I am a contractor and my dad has a fresh metered company)

    Quick warning though, as mentioned above, I would be very careful to protect your casting from any direct moisture. As thin as the concrete is there, you might be surprised at how fast water will penetrate and rust out your rebar. Hope this helps and best of luck

  20. #55
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    Default Re: Cement and re-bar ballast casting

    Also, I didn't notice in the pictures, but if you don't have any rebar cross wise in the casting, then use great care in moving it. There is the risk of splitting right down the length of it. A thin steel plate on top, that can be tightened to the casting using all of your anchor bolts would greatly reduce that risk until it is mounted to the keeel

  21. #56
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    Default Re: Cement and re-bar ballast casting

    A heavy layer of glass in epoxy all around would add some transverse strength.

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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by Gib Etheridge View Post
    A heavy layer of glass in epoxy all around would add some transverse strength.
    True, but in keeping with the low cost approach a surface bonding cement may suffice. A coat of waterproofing paint for basement walls or pools is also a good idea.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

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    Default Re: Cement and re-bar ballast casting

    Low cost is why I suggest the plate. If the rebar was also installed transverse, then it's a moot point and all that's needed is a waterproof sealer

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    Default Re: Cement and re-bar ballast casting

    How long are you letting the casting sit before you have to move it? Typically full cure and full strength isn't reached for 28 days

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    Default Re: Cement and re-bar ballast casting

    Also, the extra water to make it flow will slow cure rate and can reduce final strength. (This is meant as more a warning to anyone else who wants to go this route)

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    Default Re: Cement and re-bar ballast casting

    I have internal ballast, which in my craft is a concrete-lead mixture. When I gutted the cabin, I found that the tops of the ballast were "sealed" with straight-up polyester resin--about 4 mm thick. This had failed almost everywhere, and I found that the top few inches of concrete had deteriorated so much that I used a shovel to dig out the loose stuff:

    a52.jpg

    To build up again, I used a concrete wetted out with epoxy. I feel good about the watertight integrity of the material. Of course, I glassed over everything too. Here the dark stuff is the epoxycrete, and the red stuff is West Epoxy and the West low-density filler.

    a131.jpg

    And then the glass.

    a132.jpg

    Do you have plans to seal over the top of the concrete? If it's in a bilge area, I would think it's necessary.

  27. #62
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    Default Re: Cement and re-bar ballast casting

    With apologies to the OP...

    While some lateral reinforcement is a good idea, I doubt that this keel is exactly fragile. I wouldn't drop it on a rock, but it is not going to fall apart once it has had a few weeks to cure.

    Strength develops rapidly at first, then slows down. 28 days is a reasonable time for test and schedule trade offs in mind. It peaks at 40 years. It reaches about 80% in two weeks and 90% in 28 days.
    http://www.ce.memphis.edu/1101/notes...roperties.html


    Polyester and E-glass are not very resistant to alkali, and concrete is very alkaline. Concrete in direct contact with polyester/glass isn't the best idea. A barrier coating is needed there. Why the concrete surface degraded in the last post would require a lot more information before speculating here.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  28. #63
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by MN Dave View Post
    So, not for the OP who does not need my advice. -- A layer or two of heavy gauge wire fence might have been a good idea. As for galvanized: https://galvanizeit.org/education-an...y-coated-rebar
    Your posts are usually containing good solid advice, backed with verifiable links and info, so please do continue. Might have been hard to spot in the photo, but there is some mesh running across the centre section between the bolts. I concur that having a layer of bar would have been a fine way to gain strength across the casting, but those bars were the devil to cut by hand, and i had run out of cutting discs for the grinder. All valid points, i think by the time it is bolted up against the floor, splitting down the middle, or anywhere, would be less likely. Thanks for the response.

  29. #64
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by BHaines View Post
    Skaraborgcraft, thank you for sharing this. I have often wondered about concrete for ballast. (It's a ready available material for me since I am a contractor and my dad has a fresh metered company)

    Quick warning though, as mentioned above, I would be very careful to protect your casting from any direct moisture. As thin as the concrete is there, you might be surprised at how fast water will penetrate and rust out your rebar. Hope this helps and best of luck
    Thanks for you follow up posts. I see the re-bar as the ballast and the cement just the medium to hold it all together. I am aware of the thin skin thickness, there was some water retarder admix in the crete, but it will get a coating of something on the exterior before going into service.

  30. #65
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by koyunbaba View Post
    I have internal ballast, which in my craft is a concrete-lead mixture. When I gutted the cabin, I found that the tops of the ballast were "sealed" with straight-up polyester resin--about 4 mm thick. This had failed almost everywhere, and I found that the top few inches of concrete had deteriorated so much that I used a shovel to dig out the loose stuff:



    Do you have plans to seal over the top of the concrete? If it's in a bilge area, I would think it's necessary.
    Nasty! You did a great job on the repair work! This casting is outside of the boat, or at least only the bottom face is, it will be inset inside a 2in wood keel with another 1in wood floor above. I might need to add a sketch so its clear just how this is intended to work.
    Using an epoxy resin might have worked, though for my application, i have better use for the 6 litres of resin it might have consumed.
    Did you re-ballast using lead and concrete? Thanks for posting.

  31. #66
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    Default Re: Cement and re-bar ballast casting

    Thanks for all the responses. Was Sunday that boring? I might remove the sides of the mold today, or at least a short end to see if it solid enough to remove all. It can sit where it is all winter if needs be, i only need to take a pattern from the bolts so i can add floors to the keel plank.
    A bigger decision is to build upside down or upright, and wether to fit the casting last to make turning the hull easier; though its not overly heavy. I do have the option of building the entire boat on its 1in keel floor, that would allow making the sub shoe and casting in one unit, that can be glass sheathed and copper coated, that the boat could be lowered onto. My experimental mind is still churning, the original boats might have had a disposable outer layer, im thinking a heavy glass bottom is more suited to this northern climate and temperture changes, and rough handling on and off a trailer. I will add a sketch later, always interested in how others might deal with the same situation.
    Agree with what you said Phil Y.

  32. #67
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by MN Dave View Post
    With apologies to the OP... No apologies needed!


    Polyester and E-glass are not very resistant to alkali, and concrete is very alkaline. Concrete in direct contact with polyester/glass isn't the best idea. A barrier coating is needed there. Why the concrete surface degraded in the last post would require a lot more information before speculating here.
    I often use G4 polyurethane, to seal timber, and it can be used as a primary sealer and bond/tie coat on concrete,wood or steel when laying up with polyester or epoxy....the bond is only as good as the polyurethane to its substrate, but i have never had any failures in over 20 years. If i recall the instructions on the can, they do suggest waiting 30 days before coating, even though it is moisture curing.

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    Default Re: Cement and re-bar ballast casting

    There are a myriad of epoxy based concrete sealers on the market. Usually also cheaper then "boatbuilding" epoxy. Look for the cheapest 100% solids epoxy coating available in your market. Garage floor (swiming pool, etc.) sealers, primers, etc. all work because 100% solids means they are basicly straight epoxy resin. You can even laminate fiberglass with the thinner ones.
    The other option would be chlorinated rubber paint, but since it's mostly used for swimming pools it tends to come in large tins wich might make it uneconomical.

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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by Rumars View Post
    There are a myriad of epoxy based concrete sealers on the market. Usually also cheaper then "boatbuilding" epoxy. Look for the cheapest 100% solids epoxy coating available in your market. Garage floor (swiming pool, etc.) sealers, primers, etc. all work because 100% solids means they are basicly straight epoxy resin. You can even laminate fiberglass with the thinner ones.
    The other option would be chlorinated rubber paint, but since it's mostly used for swimming pools it tends to come in large tins wich might make it uneconomical.
    All good advice there. My friends ferro boat was covered 100% with chlorinated rubber, and i have even used it on a plywood hull with great success, the ease of overcoating in less than ideal conditions being just one of its prime attributes.

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    Default Re: Cement and re-bar ballast casting

    So after knocking one end off, i deemed it solid enough to take away the former sides.

    PICT5803.jpg

    Looks pretty well covered there....

    PICT5805.jpg

    ...and the underside looks promising, and quite smooth.

    PICT5806.jpg

    I wont move it until i have to, i can store it on edge to take up less room. At some point i will load it on my trailer so i can get an accurate weight.

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