wheat flour epoxy additive

Discussion in 'Boatbuilding' started by Collin, Nov 2, 2012.

  1. Collin
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    Collin Senior Member

    I thought about just making a fillet joint, then putting the piece in the lake for a week and seeing if the fillet or the ply gave first.
     
  2. PAR
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    PAR Yacht Designer/Builder

    Assuming the fillet is well mixed, the plywood well prepped and the fillet applied and sized properly, the failure will be in the wood fibers after a week soak. Of course, this doesn't tell you much, except you followed established practices and got the predictable results, they where designed to impart.

    My tests will run the usual gauntlet, being moisture absorption, compression, tension, elongation, peel strength, accelerated durability, accelerated UV exposure,, etc. Moisture absorption will be tested at 1, 3, 7, 14 and 30 days. Naturally, all will contain a base line sample for comparative purposes. I have a few different products on hand to test, including one from an epoxy vendor that's a member of this forum and one of his new products (relatively). Initial data will be available about the first of the year.
     
  3. Frosty

    Frosty Previous Member

    If the mix --flour or otherwise absorbs the epoxy then it will thicken without increasing bulk. If you mixed with cement dust for instance bulk and thickness would result.
     
  4. Pericles
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    Pericles Senior Member

    Frosty,

    Curiously, the volume of cement in the mixing tray did not increase by very much at all when mixed with resin, which I put down to the fact that the air spaces between the particles were filled with resin. A bit like dry mixing the materials for concrete; adding water reduces volume, by displacing air.

    Thixotropic properties also seemed unchanged, because the mixture flowed easily over the bottom surface of the skiff. Had I added more cement, then perhaps the mixture would have stiffened, but cement is heavy and I would not care to fillet joints with it. Looks very SR-71 though. :cool::cool:

    Regards.
     
  5. Herman
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    Herman Senior Member

    On industrially mixing in powders into liquids: If you want to do it right, you need a dissolver. Basicly a toothed disc, which spins such that the tip speed is 21 m/s. The blade should be about 1/3 of the diameter of the container.

    [​IMG]

    We have a 20 HP version, for 1000 lbs loads, but there are versions available up to 300 HP. (I think ours is already scary to operate, I do not think I wish to be around if they start up the 300 HP variant.)
     
  6. Collin
    Joined: Nov 2011
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    Collin Senior Member

    How much moisture absorbtion is expected for epoxy or a fillet?

    I'm reluctant to completely seal the inside bottom of a boat or the chines with epoxy because I assume some water would get in no matter how well I sealed it and never ever dry out.
     
  7. Pericles
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    Pericles Senior Member

    Herman,

    If I ever need to mix 1000lbs of epoxy resin and filler I shall know who to consult, but wouldn't a 20hp outboard motor do the job? Once!!! :D :D

    Collin,

    Your reluctance to completely encapsulate the interior of a boat (built with marine ply I presume), because you assume that water will get in, becomes a self fulfilling prophecy. The water will get in because you didn't keep it out. If epoxy works on the outside of the boat, it will work on the inside. Bilges should be waterproof.

    Vicem Yachts are totally encapsulated.

    http://www.vicemyacht.com/index.php?page=cold_molded_leader

    So are Jarrett Bay Boats.

    http://www.jarrettbay.com/

    & many others.

    http://scarboroughboatworks.com/boatsInProgress.html

    Regretably, on this occasion, your contribution is less than helpful.
     
  8. Crag Cay
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    Crag Cay Senior Member

    I have to go to Scarborough this week and was quite excited to see there was a boatbuilder there I haven't heard of.

    Except he's not there. Damn.
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Epoxy only works as a sealer, if you fully encapsulate. Anything less is just a hard plastic coating.

    Marine epoxies will keep moisture vapor transmission below 3%. This sounds significant, until you understand how things work. Wood rots, develops mold, mildew and expands and contracts, when it gets over 17% moisture content. Below this threshold, there's a minor amount of movement down to 15%, but rot and the other beasties can't survive. Once below 15% the wood is stable and not likely to rot either.

    Enter the epoxy formulators recommendations of 12% moisture content. This number has been selected because, assuming a less then 3% gain in moisture vapor transmission, you're still below the threshold where ugly things happen, like rot, moisture gain movement, etc. You can push this raw wood content level up a few percent, but you will be treading on less predictable ground.

    This is how epoxy stabilizes wood. It keeps the moisture content below the percentage where issues crop up. It also maintains this level, so wood stays dimensionally stable. It can only do this with every square inch of surface, inside holes, end grain, everything has a minimum of 10 mils of epoxy coating it. 3 coats on softwoods and 2 on most hardwoods will do.

    Anything less then full encapsulation and it's just expensive plasticized painting. Epoxy coating only parts of a structure is a waste, unless it's holding a sheathing (fabric). This stuff is well documented and available at several sites, as well as books.

    If working with an existing structure, then encapsulation is difficult. In these cases, epoxy isn't the best choice, unless (again) you're applying a sheathing. Epoxy doesn't make a very good impact barrier alone, it needs reinforcement. It also doesn't offer much abrasion resistance (alone), unless it's reinforced or the coating is quite thick.
     
  10. Frosty

    Frosty Previous Member

    Makes you want to go steel doesnt it?
     
  11. Pericles
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    Pericles Senior Member

    Frosty,

    We're going to have start calling you Rusty. :p
     
  12. KDB955
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    KDB955 New Member

    Hey folks,
    Don't know quack about boats (i'm here to learn) but I do know some organic chemistry.
    Those of you using organic fillers like wood or rice flour might get a somewhat stronger filler out of pure starch. The molecules in flour are going to be several different lengths and pure starch will have only two. Mostly the longest. I am not sure if that nano scale difference will make any difference in the strength of the finished product but I'd kinda be surprised if it didn't.
    carboxymethyl modified starch, the kind they use in adhesives, would be strongest.
    Also, I asumeboat supply places sell the pecan flour as an additive because bugs don't like it.(most nuts have arsenic compounds and such in them to discourage insects etc.).
    Adding a lead (shudder) or silver compound to the starch would keep microbes off of it.
    If someone actually does strength testing on fillers I would be very curious to see how common corn starch held up.
     
  13. Steve W
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    Steve W Senior Member

    A (the) major reason for the use of the wood and pecan flours vs the minerals is color when working with plywood that you want to bright finish, strength is rarely an issue as for the most part the filet is overlaid with fiberglass tape.

    Steve.
     
  14. PAR
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    PAR Yacht Designer/Builder

    The epoxy molecule is too big, to take advantage of the structure in starch and also one of the reasons for fibrous filler choices. Lastly, starch's elongation properties would be as good a match for typical resin formulations.
     

  15. Collin
    Joined: Nov 2011
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    Collin Senior Member

    But after time, wouldn't an epoxy sealed boat that lived in the water begin to absorb water (very slowly)? I like the idea of sealing the exterior of a boat, but just painting the interior for homebuilt boats.

    That way if water gets in, it can evaporate through the wood and paint and dry out. But if there are no leaks, the epoxy still keeps all the water out. This also keeps the cost down in epoxy savings and time down in time you scrape all the epoxy to get a good finish.

    You even see plywood kayak designs that tell you to fiberglass the inside o.0
     
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