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Thread: Cement and re-bar ballast casting

  1. #71
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    Default Re: Cement and re-bar ballast casting

    PICT5807.jpg

    Hopefully the drawing will be large enough to see the detail in the bottom right corner, and why i have the option to build the boat on 1 layer of keel, and add the ballast and outer keel layers after , if i can figure a decent way to join them.
    EDIT: I know i mentioned it some place else, but as a reminder, most of the Atkin box keel boats had internal ballast, but plans (some) were revised later to include outside lead ballast, set up in between fore n aft dead woods. I will still have room for some flat lead sheet ballast if i need it, and at a later date decide to re-fit a plate steel ballast of the correct weight if deemed required. I already know she will be a little on the tender side, but its all a trade off......
    Last edited by skaraborgcraft; 09-17-2018 at 07:25 AM.

  2. #72
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by skaraborgcraft View Post
    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.
    Yeah, that epoxycrete was pretty expensive, but overall I probably used just a few gallons.

    I have no need to reballast. The vast majority of the ballast was intact (and invisible). I needed only to address the deterioration of the top.

    Thanks for the clarification, and the compliment!

  3. #73
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by skaraborgcraft View Post
    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.
    The PU might be fine with the moisture, but it might affect the cure of the cement or the water in the cement might... Oh bullocks, It will take me 28 days to understand why, and by that time it won't matter. I think this link is talking about two kinds of sealer with the 24 hours and 28 days. http://www.ce.memphis.edu/1101/notes...ual/Chap12.pdf
    Application of any sealer should only be done on concrete that is clean and allowed to dry for at least 24 hours at temperatures above 16C (60F). At least 28 days should be allowed to elapse before applying sealers to new concrete.
    .
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  4. #74
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    Default Re: Cement and re-bar ballast casting

    Excellent link Dave. Im going by past ferro boat practice, covering the slab with cotton sheets and keeping it damp for at least another week, i wont gain anything from a fast cure, and as its a rather thin cast with a lot of metal, i prefer as strong a concrete as i can get,with less chance of dry cracking, using the materials i had. I certainly would not put any PU coating on within 14 days..at least, some of the modern barrier coats, can be put on within hours, but im not up to speed on these.
    I had never heard of boiled linseed and mineral spirits being used to seal concrete, that is definately a route i could go down if going for an embedded tar slab without any sheathing. Thanks for posting, good info.

  5. #75
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    Default Re: Cement and re-bar ballast casting

    The 24h and 28 days refference above means first cure then apply coatings only on dry surfaces. The dry part is relevant for open air structures (bridges, etc.) wich might get rained on.

    Linseed oil polimerizes to linoxyn, known to us from linoleum. If you thin it enough it penetrates the concrete then polimerizes in the presence of oxygen. It needs a lot of thin coats, time, and preferably heat to build enough film thickness. Spraying the slab in a hot summer multiple times a day will probably work. If you do it enough you end up with cast in place linoleum over your concrete. It works the same with wood by the way.

  6. #76
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    Default Re: Cement and re-bar ballast casting

    Thanks Rumars, i have plenty time to make that choice and do some more research. Hard to know effective the water retarding admix is, and how that might effect any other type of sealer penetration. If it ends up under a sheathing of some sort, then surface bond might be an issue. I think a quarter inch gap around the slab to be filled with something flexible might be a good idea, i know the expansion rates are completley different to wood, not that there will be huge movement in a 14in wide casting, but it might aid getting it out further down the line, if required.

  7. #77
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    Default Re: Cement and re-bar ballast casting

    After the concrete is cured the admixes make no difference in sealer penetration or adhesion. Epoxy does not really penetrate, it builds a surface layer anyway. Expansion rates are not a problem for a submerged slab fastened under the keel. The fore-n-aft deadwood will expand some (depends on wood species and grain orientation) but concrete is strong in compression, so no problems there. The gap with flexible sealant will be more for protecting the wood.

    One after the fact observation, maybe it will be usefull to someone thinking of doing the same. The ballast slab can be made as a structural member replacing the keel and deadwood. For that make the slab as wide as the keel and weld the rebar into a 3D mesh structure. Basicly what you did but with transverse layers added and everything welded at all crosspoints. For ataching the ballast to the deadwood fore and aft extend some rebar pieces from the faces. This gets glued in holes in the deadwood with thickend epoxy. If extreme strength is desired make this rebar as long as the entire deadwood and weld some plates across to take bolts fixing the floors, stem and sternpost. On top of it all comes a keelplank whose only function is to seal the boat to the garboads. If traditional construction without epoxy is desired one can laminate the deadwood with nails and bed everything in a flexible sealer, but in this case galvanized rebar should be used for the extensions.

  8. #78
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    Default Re: Cement and re-bar ballast casting

    Reading Rumars post reminded me of something about concrete. I was anchored off the BASRA (Bahama Air Sea Rescue Assoc) in Nassau and went into their office to ask questions about wreck sites. Boat construction came up...I was told concrete boats were the first to break up and it took very little pounding to turn them into small pieces. 2nd worst was fiberglass and it was holed but not as quickly destroyed. Wood withstood grounding and pounding longer than concrete or fiberglass before major damage. Steel usually lived for another day.

  9. #79
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    Default Re: Cement and re-bar ballast casting

    It looks like you used a pre-packaged mortar mix for the casting of bearing pedestals. That is a good choice in your case. It will likely be highly impermeable, and might be shrinkage compensated and have a corrosion inhibitor. A good concrete mix design can also be highly impermeable. Keep your casting wet for a week.
    There are epoxy paints for concrete that will last 40 years in the tidal splash zone if you are worried about durability ( http://www.kaufmanproducts.net/pdf_f...ng/740-745.pdf and similar). There are also epoxy mortars you can use ( http://www.pilgrimpermocoat.com/asse..._Grout-Pak.pdf and similar).

  10. #80
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    Default Re: Cement and re-bar ballast casting

    ^ Yes, its formulated for just that and to work with steel reinfocement, though i will say usually with a much greater skin thickness over the steel.
    Im going to be keeping my eyes open for a local source of chloro-rubber, though it might be another paint not sold to "joe-public"; in which case a 100% solids concrete floor sealer/paint will most likely be the way forward. I note on the link the prep was for a rough surface "like sandpaper", im thinking my slick bottom (if it really is when i flip it), is going to need some roughing up. Thanks for posting.
    Casting is being damped down twice a day, i will stop that after this week.

  11. #81
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by BillP View Post
    Reading Rumars post reminded me of something about concrete. I was anchored off the BASRA (Bahama Air Sea Rescue Assoc) in Nassau and went into their office to ask questions about wreck sites. Boat construction came up...I was told concrete boats were the first to break up and it took very little pounding to turn them into small pieces. 2nd worst was fiberglass and it was holed but not as quickly destroyed. Wood withstood grounding and pounding longer than concrete or fiberglass before major damage. Steel usually lived for another day.
    The variables are huge to say that with any confidence. I have met 2 ferro boat owners who went up on reefs with glass and wood boats in a storm, and they were the only ones to get off without damage so severe they had to scrap the boat. Even steel boats, with the right rock, the right speed, the right angle can be holed, ive seen it myself.
    Not all boats are built equal, even from the same materials, i think its a little unfair to judge them as if they were. I will concede that ferro is known to have a weakness for point impacts, some have mitigated that with glass lay-ups on the interior, and yes if I have to go aground in a storm on a rocky ledge, i will take steel everytime, but i try to avoid that, and i do not build boats with that scenario mind, otherwise i would be posting on a steelboats forum.

  12. #82
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    Default Re: Cement and re-bar ballast casting

    If you don't find rubber paint from a local supplier you can order it from amazon germany. From sweden trough this site: https://byggochverktyg.se
    Examples (there are more):

    https://byggochverktyg.se/Lackfabrik...-ml/B00E660JDC
    https://byggochverktyg.se/Jaeger-Kro...-ml/B005MH6UX2

    What I don't know is if it makes economical sense to buy like this compared to local prices for epoxy.

  13. #83
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    Default Re: Cement and re-bar ballast casting

    Thanks Rumars, saved me a bit of net time there! I have used chloro on wood, i will have to check prices and shipping, but i might end up using cholro on the exterior and interior, though epoxy systems without a boat picture on them are usually good value. Edit to add, my last 30kg of epoxy resin came up from Holland, at significant saving.

  14. #84
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by skaraborgcraft View Post
    The variables are huge to say that with any confidence. I have met 2 ferro boat owners who went up on reefs with glass and wood boats in a storm, and they were the only ones to get off without damage so severe they had to scrap the boat. Even steel boats, with the right rock, the right speed, the right angle can be holed, ive seen it myself.
    Not all boats are built equal, even from the same materials, i think its a little unfair to judge them as if they were. I will concede that ferro is known to have a weakness for point impacts, some have mitigated that with glass lay-ups on the interior, and yes if I have to go aground in a storm on a rocky ledge, i will take steel everytime, but i try to avoid that, and i do not build boats with that scenario mind, otherwise i would be posting on a steelboats forum.
    I hear ya and there are always exceptions...but BASRA sees hundreds of wrecks every yr and has done so for decades. I'd say they have credible understanding of what normally happens to boats that go on reefs. The only people I know of who plan on surviving hard groundings are steel boat builders.

  15. #85
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    Default Re: Cement and re-bar ballast casting

    Quote Originally Posted by BillP View Post
    I hear ya and there are always exceptions...but BASRA sees hundreds of wrecks every yr and has done so for decades. I'd say they have credible understanding of what normally happens to boats that go on reefs. The only people I know of who plan on surviving hard groundings are steel boat builders.
    I certainly dont want to dismiss their own experience, as you point out, always exceptions. A topic like this can be an endless debate.

    The chlorinated rubber seems to be an expense way and above the local epoxy floor paint, so i will probably go down that route. I have some epoxy coal tar to try out, i believe the tar content is no longer allowed due to carcinogenic nature, and replaced by a bitumen compound. Probably a good choice for the top face if bedded on a goopy tar/bituman non-stick mixture.
    Bit surprised with all the posts, most unexpected. I will update when im due to turn the slab in another week and we get to check the underside.....hopefully we will not see any re-bar poking out.....thanks for all informative links etc.

  16. #86
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    Default Re: Cement and re-bar ballast casting

    After a week of damping down and 9 days after the pour, time to flip. I used a bit of timber as a lever and a blocking pad on the opposite side. Nothing that strenuous, though nothing you want to dump on your toes!

    PICT5808.jpg

    Pretty slick under there...

    PICT5810.jpg

    The white lines are the oiled hardboard spacers used to keep the metal content off the bottom. I can dig those out and fill the gaps. A bit of air entrapment under the plastic on the forward end, surprised the weight did not force it out, not deep and easily filled. Not 100% ready to tick off the completed list, but good to get it done.

    PICT5809.jpg

  17. #87
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    Default Re: Cement and re-bar ballast casting

    Nice work. Really good to see a different approach to design and build.

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