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  1. #1
    ghost123uk's Avatar
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    Repairing small internal cracks in tight spaces

    Hi folks, been aero-modelling for 40 years, mostly control line aerobatics etc, with Balsa and nylon, I am new to fibreglass.

    I've had a nice outrunner powered 2 meter aileron glider for a few years now and it now needs a bit of TLC to the areas around the wing fixings inside the fibreglass fuselage.

    Trouble is it is small in there and the re-enforcement only needs some glass cloth (or similar ?) around 2cm x 1cm. I have got some very lightweight woven glass cloth (from a friend who uses it to skin wings on Team Racers) and I have got some Flair brand resin.

    I simply cannot get the small patches to stick where I need them. I just get in a right mess with the patch sticking to everything (fingers, small brushes, etc) and it won't stay neatly in the right place. I end up pulling the mess of cloth out before the resin fires so as not to leave a "set" mess in the tight space !

    Any tips folks ?
    JB in N.W. UK - (if you are into control line in my area, get in touch)

  2. #2

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    RE: Repairing small internal cracks in tight spaces

    Having the same problem with a Super Dimona. Going to try an old trick that worked well in other areas: spray area or cloth with a light coat of 3M 77 or equivalent. Place patch and smooth, then apply epoxy.
    Walt
    WT in Illinois

  3. #3
    ghost123uk's Avatar
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    RE: Repairing small internal cracks in tight spaces


    ORIGINAL: Walt Thyng

    Having the same problem with a Super Dimona. Going to try an old trick that worked well in other areas: spray area or cloth with a light coat of 3M 77 or equivalent. Place patch and smooth, then apply epoxy.
    Walt
    Epoxy onto g/f, I thought that was a no no ? (as in does not bond at all well)
    JB in N.W. UK - (if you are into control line in my area, get in touch)

  4. #4
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    RE: Repairing small internal cracks in tight spaces

    Epoxy bonds better to polyester resin (fiberglass resin) than polyester to polyester . wyowindworks has a short video on the subject someplace.

    Ken
    Sent from my Dry-Erase-Board

  5. #5
    ghost123uk's Avatar
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    RE: Repairing small internal cracks in tight spaces

    ORIGINAL: kenh3497

    Epoxy bonds better to polyester resin (fiberglass resin) than polyester to polyester . wyowindworks has a short video on the subject someplace.

    Ken
    Fair enough Ken, I only mentioned it because whilst doing some searching on here before posting, I found a whole load of pages discussing it and I kinda got the idea that unless you clean with solvents and rough up the surface it ain't such a good idea. Perhaps I miss-read it and they meant glueing to the gell coat (obvious now as I think about it )
    JB in N.W. UK - (if you are into control line in my area, get in touch)

  6. #6

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    RE: Repairing small internal cracks in tight spaces

    I would recommend what Walt suggested. A light mist of 3M Super 77 on one side of the glass, position, and saturate. You can probably just saturated the glass with thin CA and be just fine for the repair. I've done many composite field repairs this way and they are still holding up. In fact, I've made CA saturated composite repairs to fuses that were broken in half. Upon impact the fuse broke somewhere else.

    You should sand and clean the area to be repaired regardless of the resin choice. If the original fuse is made with polyester finishing resin it will have a wax coating on it that will inhibit any bond. You can 3M somesandpaper to the tip of a dowl rod to do the sanding and use a Q-tip with solvent to clean the area. Sanding and cleaning is a basic step when making ANY bond/repair with composite materials with ANY resin.

    Epoxy laminating resin, regardless of the substrate, makes the best repair. If the area requires an HDT of around 200*F then you can do the repair with Vinyl Ester and overlap the repair by several inches. Vinyl Ester can reach an HDT of 200*F with a room temperature cure. In models it is pretty rare that a HDTof 200*F is required so epoxy laminating resin is a safe first choice.

  7. #7

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    RE: Repairing small internal cracks in tight spaces

    I always when doing fibreglassing tack woven cloth in place with a bit of super glue holds clotth in place so I can get resin on to it without cloth moving

  8. #8
    ghost123uk's Avatar
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    RE: Repairing small internal cracks in tight spaces


    Thanks for the suggestions and in fo folk

    I will try the CA with cloth thing, though I think I will try and find some heavier grade woven cloth as the stuff I have is gossamer thin and I think this might be contributing to the problem of keeping it in the right position and "flat".
    JB in N.W. UK - (if you are into control line in my area, get in touch)

  9. #9

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    RE: Repairing small internal cracks in tight spaces

    Here is a trick that I have used on full scale aircraft and restoring cars. First sand and feather the aera that needs repair. Chop up the fiber glass cloth as fine as you can.  Mix the chopped glass in with the resin. Paint the concoxtion into the flawed aera. If you are not able to vacume and bag the repair dont wory, let it cure at room tempeture. After it cures you can conture and sand without wory of compromise of the strength.  Good luck .

  10. #10

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    RE: Repairing small internal cracks in tight spaces

    Here is a trick that I have used on full scale aircraft and restoring cars. First sand and feather the aera that needs repair. Chop up the fiber glass cloth as fine as you can.  Mix the chopped glass in with the resin. Paint the concoxtion into the flawed aera. If you are not able to vacume and bag the repair dont wory, let it cure at room tempeture. After it cures you can conture and sand without worry of compromise of the strength.  Good luck .

  11. #11

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    RE: Repairing small internal cracks in tight spaces

    I have found it important to sand the crack and an area each side of the crack 1/4" to 1/2'. I use 80 grit. I use the sticky back sand paper from Tower on various sand blocks, some round dowl and some rectangular wood blocks.
    SidGates
    Web: http://www.sidgates.us


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