Page 1 of 3 12 ... LastLast
Results 1 to 35 of 87

Thread: Cement and re-bar ballast casting

  1. #1
    Join Date
    Jan 2010
    Location
    Northern Europe
    Posts
    9,216

    Default Cement and re-bar ballast casting

    I thought twice about starting this thread, but not everyone can afford, need or wish to deal with molten lead and costly bronze.
    My actual plan was to use a 1in thick steel plate, until i found that the local stockist was asking way, way, way more than current steel prices, and its not an item easily or cheaply shipped from the UK.........so....re-bar and cement it is.
    Not being as dense as steel plate, the casting is a little longer and wider than the plate i was going to use, and twice as thick, but with a 3in wood bottom on the box keel, space enough without creating other issues.

    PICT5790.jpg

    16mm bolts, spot welded to the re-bar. These were "expansion bolts", with the expansion ring removed.

    PICT5791.jpg

    These are around 8ft long. 3 bars each side of the bolts. These are the main "backbone" elements and weigh 20kg/44lbs

    PICT5793.jpg



    The mold is a pallet that needed an extension on the front. Some 2in square timber screwed down over heavy plastic sheet. Pretty simple given the low amount of pressure it will be under.

  2. #2
    Join Date
    Oct 2008
    Location
    Walney, near Cumbria UK
    Posts
    40,715

    Default Re: Cement and re-bar ballast casting

    Instead of using gravel in the cement, use small steel scrap. Old chain, steel balls from crushing mills, swarf from machine shops, anything that will mix easily.
    It really is quite difficult to build an ugly wooden boat.

    The power of the web: Anyone can post anything on the web
    The weakness of the web: Anyone can post anything on the web.

  3. #3
    Join Date
    Jan 2010
    Location
    Northern Europe
    Posts
    9,216

    Default Re: Cement and re-bar ballast casting

    PICT5794.jpg

    There is a 4mm strip of hardboard under the bolt heads to keep the bars off the bottom. Some timber spacers were added to keep the keel bolts in the right position, more or less.

    PICT5796.jpg

    44 lengths of 10mm bar to be loaded up by sliding in from the front, and 26 shorter bits to pack in . Steel should weigh in at 103kg/226lbs. The box volume should take almost 100kg of cement, but the steel will take up much of that volume, but i expect to use at least 3 bags, 75kg/165lbs.The first batch will have to be quite runny to ensure it flows under the rods. Thats a job for tomorrow.....hopefully a one-hit wonder.

  4. #4
    Join Date
    Jan 2010
    Location
    Northern Europe
    Posts
    9,216

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by Peerie Maa View Post
    Instead of using gravel in the cement, use small steel scrap. Old chain, steel balls from crushing mills, swarf from machine shops, anything that will mix easily.
    You got in there quick Nick before i had finished, does that re-bar satisfy you? The cement is a premix, used for casting plinths to carry houses, i wont be adding anything to it, though i do have 1000kg of granite chippings outside in bags....

  5. #5
    Join Date
    Nov 2001
    Location
    Seattle
    Posts
    24,077

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by skaraborgcraft View Post
    You got in there quick Nick before i had finished, does that re-bar satisfy you? The cement is a premix, used for casting plinths to carry houses, i wont be adding anything to it, though i do have 1000kg of granite chippings outside in bags....
    The specific gravity of cement is only about two, which means it half floats. The specific gravity of granite is around 2.75. Most steel is closer to 8. So, the benefit of mixing in a bunch of steel scrap is pretty large.

  6. #6
    Join Date
    Sep 2007
    Posts
    1,070

    Default Re: Cement and re-bar ballast casting

    If your rebar and concrete weigh the amount specified for ballast I say just do it.

  7. #7
    Join Date
    Oct 2008
    Location
    Walney, near Cumbria UK
    Posts
    40,715

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by skaraborgcraft View Post
    You got in there quick Nick before i had finished, does that re-bar satisfy you? The cement is a premix, used for casting plinths to carry houses, i wont be adding anything to it, though i do have 1000kg of granite chippings outside in bags....
    Quote Originally Posted by johnw View Post
    The specific gravity of cement is only about two, which means it half floats. The specific gravity of granite is around 2.75. Most steel is closer to 8. So, the benefit of mixing in a bunch of steel scrap is pretty large.
    Is it a dry premix? If so riddle out the stone and look for small scrap steel.
    It really is quite difficult to build an ugly wooden boat.

    The power of the web: Anyone can post anything on the web
    The weakness of the web: Anyone can post anything on the web.

  8. #8
    Join Date
    Jun 2000
    Location
    Pleasant Valley NS Canada
    Posts
    15,364

    Default Re: Cement and re-bar ballast casting

    Before you pour the concrete, you may wish to seal the steel with several coats of paint. Concrete is not waterproof; moisture will get in, and use oxygen entrained in the concrete to rust the steel. It will swell as it corrodes, eventually cracking the concrete.
    Hope for the best, but plan for the worst.

  9. #9
    Join Date
    Mar 2010
    Location
    central cal
    Posts
    14,156

    Default Re: Cement and re-bar ballast casting

    Any way to apply some mesh into the steel? Maybe a layer or two on top of and wired to the rebar. Barring that, maybe arrange and wire the extra rebar into a pattern that interlocks?

    I think a more evenly supporting armature will be better, especially when you go bumping along the bottom someday.

    I second the steel additions. Maybe weight lifting plates, like the gym type? Generally available cheap or free from folks what donít use them...

    Does this mean youíre building a bigger boat?

    Peace,
    Robert

  10. #10
    Join Date
    Oct 2008
    Location
    Walney, near Cumbria UK
    Posts
    40,715

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by mmd View Post
    Before you pour the concrete, you may wish to seal the steel with several coats of paint. Concrete is not waterproof; moisture will get in, and use oxygen entrained in the concrete to rust the steel. It will swell as it corrodes, eventually cracking the concrete.
    Or research a ferrocrete concrete mix. The proper mix chemically bonds to steel which is why ferrocrete boat hulls are still in service.
    Apparently the mix is 1 part Portland cement to 3 pars clean sand.
    It really is quite difficult to build an ugly wooden boat.

    The power of the web: Anyone can post anything on the web
    The weakness of the web: Anyone can post anything on the web.

  11. #11
    Join Date
    Jan 2010
    Location
    Northern Europe
    Posts
    9,216

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by mmd View Post
    Before you pour the concrete, you may wish to seal the steel with several coats of paint. Concrete is not waterproof; moisture will get in, and use oxygen entrained in the concrete to rust the steel. It will swell as it corrodes, eventually cracking the concrete.
    Its a valid comment and i have seen blown concrete from internal rust. However, i have also seen plastered numerous steel and mesh ferro boats that have been allowed to weather before plaster day, one of which i know has been pretty much in the water for the last 25 years with no issues, suggesting that what is used to seal the concrete is probably more important. The casting might get a wrap in glass, or at the very least, coated with epoxy coal-tar, which seems to protect steel for a good time period. It can easily be swapped out for the steel plate at a later time.....

  12. #12
    Join Date
    Jan 2010
    Location
    Northern Europe
    Posts
    9,216

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by amish rob View Post
    Any way to apply some mesh into the steel? Maybe a layer or two on top of and wired to the rebar. Barring that, maybe arrange and wire the extra rebar into a pattern that interlocks?

    I think a more evenly supporting armature will be better, especially when you go bumping along the bottom someday.

    I second the steel additions. Maybe weight lifting plates, like the gym type? Generally available cheap or free from folks what don’t use them...

    Does this mean you’re building a bigger boat?

    Peace,
    Robert
    Yes to mesh and interlocking. There will not be much room between the bars for anything but concrete, less than 1/4in, which i consider to be a minimum skin thickness of concrete, and the bare amount to hold all the re-bar together as a casting. Experts can cover mesh hulls half that amount when fairing. It will have to support the boat when launching and recovering on a trailer, so robust skin thickness a good idea, even if it gets sheathed after.

    This means im starting a bigger boat......i did find new homes for 4 others, so i have some room........

  13. #13
    Join Date
    Mar 2010
    Location
    central cal
    Posts
    14,156

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by skaraborgcraft View Post
    Yes to mesh and interlocking. There will not be much room between the bars for anything but concrete, less than 1/4in, which i consider to be a minimum skin thickness of concrete, and the bare amount to hold all the re-bar together as a casting. Experts can cover mesh hulls half that amount when fairing. It will have to support the boat when launching and recovering on a trailer, so robust skin thickness a good idea, even if it gets sheathed after.

    This means im starting a bigger boat......i did find new homes for 4 others, so i have some room........
    Sweet!

    Sweet, Sweet, Sweet!

    Peace,
    Robert

  14. #14
    Join Date
    Apr 2010
    Location
    South Australia and Tasmania
    Posts
    15,237

    Default Re: Cement and re-bar ballast casting

    Steel punchings or whatever are often used when concrete is poured inside a hull. On an external keel I'd worry that steel might be very close to, or even on, the surface of the concrete, and exposed to water. I think your use of rebar, where you can maintain a controlled depth of concrete before you hit steel, is a much better idea. Corrosion problems arise where the steel is too close to the surface.

  15. #15
    Join Date
    Jan 2010
    Location
    Northern Europe
    Posts
    9,216

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by navydog View Post
    If your rebar and concrete weigh the amount specified for ballast I say just do it.
    The absolute minimum would be 60% of max fuel load which is "only" 120kg/264lbs. In my case, aiming at 200kg of ballast allowing for a loaded displacement up to 2.6 to 3.2 tons,ratios i have seen for some motor cruisers. Being sail assisted, a bit more is use full. We can use the weight of heavy items that cannot move as part of the ballast equation, the engine low in the box keel, battery,anchor chain for example, an extra 300kg/660lbs. Only around half a ton, enough for self righting, but keeping trailer weight within reasonable limits.

  16. #16
    Join Date
    Jan 2010
    Location
    Northern Europe
    Posts
    9,216

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by Phil Y View Post
    Steel punchings or whatever are often used when concrete is poured inside a hull. On an external keel I'd worry that steel might be very close to, or even on, the surface of the concrete, and exposed to water. I think your use of rebar, where you can maintain a controlled depth of concrete before you hit steel, is a much better idea. Corrosion problems arise where the steel is too close to the surface.
    Agree with all of that. I would not be happy with too thin a skin of concrete. I helped a friend load 1000kg of punchings into a concrete mix poured inside his steel boat, where it does a fine job.

  17. #17
    Join Date
    Sep 2007
    Posts
    1,070

    Default Re: Cement and re-bar ballast casting

    You might want to use a waterproofing additive to the mix. For example: http://www.hycrete.com

  18. #18
    Join Date
    Jan 2010
    Location
    Northern Europe
    Posts
    9,216

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by navydog View Post
    You might want to use a waterproofing additive to the mix. For example: http://www.hycrete.com
    For those that do not know, there is a myriad of potions and additives to change the composition of concrete. Yes there will be a splash of Admix added, hydrophilic crystalline type Admix being one of the better ones for concrete exposed to water pressure.

  19. #19
    Join Date
    Jul 2013
    Location
    Aquitaine
    Posts
    814

    Default Re: Cement and re-bar ballast casting

    On additives, my brother is a Civ. Eng. consultant on big projects (Burg Tower, Forth Crossing) and when I bought this up, he said just put some more cement in the mix and make sure you have coverage of the steel to a decent thickness.
    Rent a poker type vibrator to consolidate the mix. He mentioned 10% improved strength. Not so important for a keel, but will get the mix around the steel better and eliminate voids.
    A2

  20. #20
    Join Date
    Sep 2007
    Posts
    1,070

    Default Re: Cement and re-bar ballast casting

    It will still be porous with added cement.
    Last edited by navydog; 09-13-2018 at 04:51 AM.

  21. #21
    Join Date
    Dec 2001
    Location
    Northern NSW Australia
    Posts
    71,959

    Default Re: Cement and re-bar ballast casting

    I wouldn't trust the concrete mix to run everywhere you need . I'd hire a vibrator to much sure it flows into every crevice.I'd also add a bit of extra cement for a stronger mix.
    '' You ain't gonna learn what you don't want to know. ''
    Grateful Dead

  22. #22
    Join Date
    Jul 2017
    Location
    Toodyay, Western Australia
    Posts
    628

    Default Re: Cement and re-bar ballast casting

    Tyre shops may give you their scrap wheel weights by the bucketful. Not many are lead these days, but they still weigh a lot. Since they are mostly tiny things they might mix in to the crete well and fill any gaps between your rebar. I guess you've read Wizbang's account of his concrete ballast on woodwind?

  23. #23
    Join Date
    Sep 2007
    Posts
    1,070

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by Small boats rock View Post
    Tyre shops may give you their scrap wheel weights by the bucketful. Not many are lead these days, but they still weigh a lot. Since they are mostly tiny things they might mix in to the crete well and fill any gaps between your rebar. I guess you've read Wizbang's account of his concrete ballast on woodwind?
    Most tire shops have recycling setup long ago and sell the weights for scrap.

  24. #24
    Join Date
    Dec 2001
    Location
    Northern NSW Australia
    Posts
    71,959

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by navydog View Post
    Most tire shops have recycling setup long ago and sell the weights for scrap.
    I bought 2 tons of them over period, not free but good value. I used to leave 20 litre drums at tire depots and go back a week later to collect them. The hardest part is getting the drum onto the back of my ute.

    I've solved that problem these days with Chinese pickup crane.
    '' You ain't gonna learn what you don't want to know. ''
    Grateful Dead

  25. #25
    Join Date
    Jul 2017
    Location
    Toodyay, Western Australia
    Posts
    628

    Default Re: Cement and re-bar ballast casting

    I walked into the local tyre shop (maybe two years back now) and asked if I could take their scrap. They said, sure over there in that drum mate, bring the drum back and leave it where you found it... and that was that.

  26. #26
    Join Date
    Jan 2010
    Location
    Northern Europe
    Posts
    9,216

    Default Re: Cement and re-bar ballast casting

    Turns out there was not enough room for all the re-bar i had, but only 6 short bits left out. I think its important to have a good gap where the cement can flow. This is more like a reinforced concrete lintel.Below is the second layer of 5 layers of re-bar.

    PICT5798.jpg

    The mix was a bit on the wet side in order to run everywhere. Part of the reason for doing this now is that it will have time to stay wet and dry out slowly, before the frost comes. The bars and concrete where done in layers to ensure the cement was everywhere.

    PICT5800.jpg

    Now covered with old bed sheets and will be damped down when needed over the next week at least. Only used about 65kg of cement- two and a half bags. Just over 4 hours work.....need to go do something with my back.....
    Last edited by skaraborgcraft; 09-13-2018 at 01:38 PM.

  27. #27
    Join Date
    Mar 2010
    Location
    central cal
    Posts
    14,156

    Default Re: Cement and re-bar ballast casting

    You had better write your initials and the date in there...

    Peace,
    Robert

  28. #28
    Join Date
    Dec 2003
    Location
    Sound Beach, NY
    Posts
    3,534

    Default Re: Cement and re-bar ballast casting

    Very interesting. Thanks for posting, good luck.

  29. #29
    Join Date
    Jan 2007
    Posts
    122

    Default Re: Cement and re-bar ballast casting

    Skaraborg, I was right into ferro building in the 1950's with Rich Hartley, We found the best and fastest cure was L.P.steam. just wrap the hull in tarps and blankets, anything really and set up a boiler (old 44 g. drum) and steam for a couple of days, you don't need pressure, just wet steam. Are you building from the 13ft box keel proto. I downloaded all of those threads. Very interesting and a practical design. Keep up the good work.

  30. #30
    Join Date
    Mar 2007
    Location
    East Quogue,NY
    Posts
    15,718

    Default Re: Cement and re-bar ballast casting

    Very nice. Put in a gold coin or silver dollar. Doubloons work well.
    Better yet some rubber bands--good luck to help you bounce off the bottom during any groundings.

    Kidding aside; thanks for sharing.

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  31. #31
    Join Date
    Jan 2010
    Location
    Northern Europe
    Posts
    9,216

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by Breakaway View Post
    Very nice. Put in a gold coin or silver dollar. Doubloons work well.
    Better yet some rubber bands--good luck to help you bounce off the bottom during any groundings.

    Kidding aside; thanks for sharing.

    Kevin
    I have not heard of the rubber band offering, but thats a good one, i can ream out a wee hole while it is still green. The gold Sovereign usually goes under the mast step.....

  32. #32
    Join Date
    Jan 2010
    Location
    Northern Europe
    Posts
    9,216

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by rayman View Post
    Skaraborg, I was right into ferro building in the 1950's with Rich Hartley, We found the best and fastest cure was L.P.steam. just wrap the hull in tarps and blankets, anything really and set up a boiler (old 44 g. drum) and steam for a couple of days, you don't need pressure, just wet steam. Are you building from the 13ft box keel proto. I downloaded all of those threads. Very interesting and a practical design. Keep up the good work.
    I used to spend weekends in the summer with a plastering crew when i was a kid, back then it was lots of hessian sacking and hose pipe around the sheer and a cold damp cure of several months. I never got round to building one from scratch, but did fit out a bare hull i picked up for very little money.
    Yes, im intending to go full size box keel, though apart from the keel, nothing is set in stone! I will be happy to get the 3 layer floor/keel arranged, and at least the first layer glued up with end posts, so i can fit the engine mounts and shaft, at bench height with no access limitations. When i get started and have something to show, i can share it. Thanks for the interest.

  33. #33
    Join Date
    Jan 2007
    Posts
    122

    Default Re: Cement and re-bar ballast casting

    A part of my c.v. includes a period working on "Awhanee" with Bob and Nancy Griffiths. I will not enter into any pro's and cons on that boat but she sailed for close to 50 yrs before Nancy knew her time was up (both of them) and took her out and scuttled her I think in Molokai channel. I shall be watching your thread with much interest. A guy who never got any recognition in ferro boat building was Morley Sutherland, he studied civil engineering under Prof. Nervi in Italy and he was Rich Hartleys guru. regards ray

  34. #34
    Join Date
    Feb 2008
    Location
    Berlin, Germany
    Posts
    699

    Default Re: Cement and re-bar ballast casting

    Now that all's been cast, my thoughts are a bit late. HOWEVER my daysailer came with a centreboard/keel under it. The keel turned out to be a mixture of polyester (I believe) and steel punchings. The boat seems to have seen salt water in its history (original owner was in Flensburg) and bilge water (condensation) is usually a bit salty. After I bought the boat, I found that the edges of the CB slot in the keel had risen and cracked like fresh-baked buns due to the steel rusting and later, when I dropped the keel off the hull, I found the same happening at the top, threatening to affect the boat's hull. I had to rebuild the respective sections with filler and fibreglass.
    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.
    My keel after reshaping:
    IMG_0351.jpg

  35. #35
    Join Date
    Jan 2010
    Location
    Northern Europe
    Posts
    9,216

    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by rayman View Post
    A part of my c.v. includes a period working on "Awhanee" with Bob and Nancy Griffiths. I will not enter into any pro's and cons on that boat but she sailed for close to 50 yrs before Nancy knew her time was up (both of them) and took her out and scuttled her I think in Molokai channel. I shall be watching your thread with much interest. A guy who never got any recognition in ferro boat building was Morley Sutherland, he studied civil engineering under Prof. Nervi in Italy and he was Rich Hartleys guru. regards ray
    I guess the ferro-boat world has always been small, but i have heard of Sutherland, and of course Nervi was the source, of which there are many research papers of his studies and tests online.Not quite the forum for disscussion of things ferro, but i think we can agree, its not all bad.....when done right. Some friends of mine took a 50ft ferro boat from the UK to Australia a few years back, both wooden boat builders, and they both concluded they could not have built the same boat in wood on the budget they had..nuff said.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •