Fiberglass taping an inside corner

Discussion in 'Fiberglass and Composite Boat Building' started by MarkIFC, Dec 3, 2007.

  1. MarkIFC
    Joined: Jul 2007
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    MarkIFC Junior Member

    My project has a 90 degree inside corner that I want to cover with 6 oz 4" tape.
    Do I need to putty the corner to ease the curve or can I work the tape into the corner? This is more to waterproof than provide any structural integrity.
     
  2. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    Mark,
    Fibreglass cloth may feel flexible, but the individual fibres are actually quite stiff for their size. As a result, it can't- and won't- do sharp corners. Without a radius of a few millimetres, the 6 oz tape will pull away from the sharp corner, leaving a small gap behind. (Even with vacuum bagging, I have seen this happen.)
    After you've primed the joint with resin, use a popsicle stick or other small, round-tipped implement to fillet a small bead of thickened resin into the corner. You can push the tape directly into the wet fillet, then wet out as usual. All the taped joints on my glass/ply boat are done this way and not the slightest crack has developed in any of them in seven seasons.
     
  3. the1much
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    the1much hippie dreams

    matt is exactly right,,when i came to texas an "autobody" dude tried to show me "how we do it down here" he was trying to wrap a paint stick in glass to use for some stupid brace. after 30 minutes of me laughing,14 paint sticks, gallon of resin and 4 yards of glass later,, he decided it must be the material , hahaha
    matt has told you the ONLY way it will work,, you can use different materials, or filler,, but the ONLY way to do it is make ya radius ;)
     
  4. MarkIFC
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    MarkIFC Junior Member

    Can I make the radius out of anything other than the thickened epoxy? I've never worked with epoxy resin before but I foresee it being a sticky messy proposition.
    What about using something like acrylic latex caulk? Or DAP window putty? But will that interfere with the adhesion of the epoxy?
     
  5. the1much
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    the1much hippie dreams

    what kind of resin are you using?,,, make it from that,,i've never tried any of that other stuff,, but wouldnt reccomend it,,usually the "heat" and chemical reaction from you glassing over them things shrivil it and ya end up with nothing there.. you can use poly resin and cabosil or that other stuff that ya can get from auto store called fiberfill or something like that,,hull and deck putty,,, just pick something thats campatible with whatever your laying "over" it
     
  6. MarkIFC
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    MarkIFC Junior Member

    I have ordered US Composites Epoxy Resin with medium fast hardner.
    I suppose I could mix it with wood flour. I have read that regular ole bread flour works just as well? Somone else says to put the mix in a ziplock bag, cut one corner, and squeeze it out like a icing bag.
     
  7. the1much
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    the1much hippie dreams

    heh,,, never heard of it,,,,but i dont do epoxy,lol,, im an old timer i guess, i only use it when i HAVE to.i try staying with whatever "chemical" used to begin with, and try never mixing,, even tho the "epoxy" dudes say its better. you can "stick" epoxy to poly,, but not poly to epoxy.. the stuff makes me think too much and causes head rush's ;)
    but theres plenty of guys on this forum that KNOW epoxy and i would go with what they say when working with epoxy, and im sure they'll be replying soon
     
  8. marshmat
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    marshmat Senior Member

    It's only a sticky messy proposition if you spill it everywhere. Epoxy's actually a lot neater to work with than people often give it credit for.
    Stick with thickened epoxy. The caulkings and putties will just create a stress concentration where the glass actually touches the substrate, and that stress concentration will just help the thing peel off.
     
  9. lazeyjack

    lazeyjack Guest


    as you know, I am a metal man, but recently did two wooden ply dorys, chines, without tape, in the sun some joints are cracking , i used a microfibre blend, in early days we used asbestos powder, strong it was
    Trouble is I just sold one of these dories, for a fraction of build cost, IF he stores it out of our powerful sun it may be ok
    Doing it again I would NOT use tape but solid chines and screws the chines are the only extra and would be much quicker I think than tape Still as I said I,m not into that sticky stuff
     

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  10. fiberglass jack
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    fiberglass jack Senior Member

    pick up a yard of 18oz woven roven and pull the strands of roving out , get a few of the strands together and make a sort of rope with it, dip into the resin and then strain off the excess resin with your fingers place this into the corner of the joint let it tack up a little then place your cloth tape. This way the joint will be all glass with out paste
     
  11. buckknekkid
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    buckknekkid Senior Member

    thats an old Cuban /Irish trick. I have an interesting IYC story call me tomorrow
     

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  12. Moosemiester
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    Moosemiester Junior Member

    Mark
    There's lots of ways to move epoxy around -- I wouldn't reccomend the plastic bag as epoxy gets warmer (exotherms) as it cures.

    The best approach for a novice is to use fillers to thicken it up to make it easier to work with, and finish the job after the epoxy has cured by sanding. You want a high density filler, such as US Composites Cabosil/Aerosil.

    Mix up the smallest batch you can measure stir it for a couple of minutes, then add the filler in small amounts until you have something about the consistency of peanut butter. Use that to create the raduis under the tape as others have suggested.

    For the tape make another small batch, just epoxy -- a small amount of filler to keep it from being too runny is OK but don't add too much or it won't infuse the glass properly. For a little job a small brush works well, for bigger jobs you want a roller. If you brush epoxy on the surface first, and then lay the tape, it will stay put while you add more. Don't brush it like paint, just use the brush to apply it.

    Let that cure, sand it, and if you need to fill in anywhere use the thick, peanut butter variety of thickened epoxy to fill the holes.

    I'd practice with a few scraps of wood to get a feel for the stuff. As long as what you're trying to epoxy isn't dirty, or oily, you'll end up with something that's pretty darn strong.

    Wear gloves and under no circumstances should you attempt to clean epoxy off your skin with paint thinner or acetone -- let it dry and scrape it off. If you plan on doing more than 2 or three batches you'll want a decent organic respirator as the fumes are very very nasty.

    Let us know how it goes. An amatuer can do a first class epoxy job without a lot of expensive tools, that's one of the great things about this type of building.
     
  13. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    I also find that sanding the fillets smooth again prior to paint or varnish is a real pain due to the confined space and weird angle.
    I put small (4" by 6") bits of peel ply over the fillets afterwards, and smooth them out.
    It cuts the finishing work by a huge amount.
     
  14. AroMarine
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    AroMarine Junior Member

    You did not specify how long your corner was or how big of a radius would be acceptable. So here goes a couple of shots in the dark. I have not used US Composites epoxy but for water proofing with West System or MAS type resin you could get by with no fabric just resin depending on the flexibility in your joint. If you do need or want glass and epoxy is your choice use resin filled with Cabosil/Aerosil or a talc type product mixed to peanut butter consistency to make your radius and as long as everything is tacky you can put in your wet tabbing in right away. For finishing you can use peel ply or coat your work, again, while it is still tacky with epoxy and microballoons/microspheres, easy to sand after curing. If you are using polyester resins the quick and dirty radius is Bondo. It must be cured and sanded and covered with glass. Polyester resin can also be mixed with Cabosil/Aerosil to make a good putty but also needs to cure and be sanded prior to applying new glass. Again no experience with US Epoxy but others can be cleaned off skin with orange citrus cleaner keeping away from the acetone. Any gloves vinyl or rubber are still the best.
     

  15. frankrider
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    frankrider New Member


    Thanks Jack, your a legend. I am rebuilding a plywood poptop off an old 70's campervan and read this just before I had to do the internal corners. Worked like charm, no void. Thanks mate. Now I just have to get a trick for the outside corners.
    Frank from downunder.
     
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