fasteners under glass

Discussion in 'Fiberglass and Composite Boat Building' started by robwilk37, Dec 27, 2012.

  1. robwilk37
    Joined: Nov 2010
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    robwilk37 Senior Member

    any problem with just leaving the tacking/framing screws in place and laminating over them if they are in an area that will never see moisture? ive been backing them out and filling the holes before laying up the glass but i cant remember why. seems mechanical as well as epoxy bond would be superior to just the epoxy/wood interface, making the attachment 3-dimensional so to speak? fasteners are coated decking screws not stainless.
     
  2. rwatson
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    rwatson Senior Member

    Not totally clear on your situation -

    1) I presume the screws are not going through into temporary formwork, but into permanent frames or stringers ?

    2) I have a feeling too that the type and size of wood will be a consideration.

    3) The description "never see moisture" in a boat could do with a bit of detail too.
     
  3. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    I would not leave them in mate, it certainly is risky considering that they are only steel anyhow, pop em out and you don't have to wonder any more do you.

    If you feel that mechanical fastenings are required, then replace them with monel, silicon bronze, or if you are feeling wealthy, titanium.
     
  4. tunnels

    tunnels Previous Member

    Take then out !!

    TAKE THEM OUT!!!
    Eventually they wil rust and rust once it starts exspands and make small lumps . Then the rust marks start to bleed out throught the glass and appear . Dont leave one single screw any where . !!! :eek::confused:
     
  5. PAR
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    PAR Yacht Designer/Builder

    I've buried stainless fasteners hundreds of times, encased in epoxy without difficulty, but I would never try this with mild steel, certainly not black phosphate or even galvanized. I use decking and drywall screws as "setup" and assembly fasteners, but these always get pulled. On the other hand I've buried many stainless screws, entombed in goo, without a single issue. It's not something I'll do below the LWL, but on a trailer borne boat, I see no reason why they couldn't be used.

    Coated decking screws come in several types, none that I'm aware of will tolerate continuous immersion. These screws are usually mild steel with a microscopically thin coating, that is often removed when driven, just from the heat of doing so. They're generally pretty weak and the coating not especially effective in the marine environment.

    From a technical stand point, just epoxy alone will suffice, if the joint has sufficient faying surface. A mechanical fastener is redundant and offers a potential penetration point for moisture. Unless using a reasonably proud fastener (stainless, bronze, monel, etc.), remove them and trust the goo.
     
  6. jamieh3
    Joined: Jun 2013
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    jamieh3 New Member

    I think Stainless Steel screws under epoxy should be fine - but i would never remove the Oxygen on something critical as for Stainless Steel to work it needs Oxygen - E.g. Keel Bolts shouldn't be 316 Stainless for this reason, due to a lack of Oxygen in the keel + Saltwater (if it gets in at all) = bad news.
     
  7. PAR
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    PAR Yacht Designer/Builder

    Jamieh, welcome to the forum.

    I think you'll find that stainless is buried in all sorts of things with few worries. Keel bolts last decades, struts, shafts and wheels the same, as do fasteners under epoxy. There's more to the the equation than O2. Entombed in a ballast casting, no moisture, so the lack of air is moot, assuming the exposed head is also protected. Ditto underwater elements, where they are surrounded by water, but lack free oxygen, for the most part. Simply put the industry has been using stainless like this for many decades and on the surface, it does seem to fly in the face of convention, but not when you look at the data.
     
  8. CDK
    Joined: Aug 2007
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    CDK retired engineer

    There still are a few stainless screws in my right elbow. Some 60 years ago the surgeon wanted to take them out after the bone had healed, but I declined.

    It is wet, warm and salty there, but they still seem happy and show on X-ray only. Plenty of lumps in other places, like overloaded joints where the lubricating fluid oozes out, but that's a different story.
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A few years ago I had to repair a transom I had put a new core in about 10 years previous. Back then, I used a belt and suspenders approach and left in the stainless screws used to suck down the core layers, epoxying over their heads and sheathing over that. It was hit by a car and transom needed some work. I cussed those damn fasteners, as they where just as tough, shinny and hard as they where when installed 13 - 14 years previously. No rust, just buried, embalmed in goo fasteners. The boat spent 9 months out of the year on a berth.
     
  10. michael pierzga
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    michael pierzga Senior Member

    Metal creates moisture in the hot cold cycle. Condensation.

    Additionally how will you achieve a good epoxy bond when you have a fastener head washer and nut.

    Fasteners under glass is bad craftsmanship
     
  11. PAR
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    PAR Yacht Designer/Builder

    You're incorrect Micheal. Condensation only requires moisture vapor and varying temperatures. If none is present (one or the other), there's no condensation. Fasteners buried in wood usually don't have a washer, just a flat head, which is is to entomb in goo. Fasteners aren't strictly under 'glass, but embedded in epoxy, which is then covered with a sheathing if desired.
     
  12. LP
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    LP Flying Boatman

    Ohhhh........... The sins I've committed.:rolleyes:

    Trying to rectify it on my newest build, but when the head of a drywall twists off on retraction, well...sometimes I just let the dead dog lie. :eek:
     
  13. PAR
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    PAR Yacht Designer/Builder

    I have a home made tool for this LP. It's a length of steel tubing (several) with teeth cut into it. I pick the one that fits around the wayward fastener and plow down it's length. A whack with a hammer, maybe some cussing time with a scratch awl or something and it's ready to get plugged with a dowel.
     
  14. LP
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    LP Flying Boatman

    Kind of like a pilotless hole saw.

    Nice. :idea:
     

  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Yeah, pretty much. You kind of start it at an angle and square up with the fastener as it digs in around the shank.
     
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