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  1. #1

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    Fibreglassing over Balsa

    Question for you
    I am building a 1/5th scale DHC Beaver. The entire plane is skinned in 1/16 and 1/8 balsa. I was originally going to cover her with Solartex fabric but have since thought that glassing her using water based Poly Urethane might work well.

    Does anyone have any advice on the idea and or point me in a direction or advice on how to fibreglass using water based Poly Urethane.

    Any advice or direction would be helpful.

    Colin

  2. #2
    invertmast's Avatar
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    RE: Fibreglassing over Balsa

    Not WBPU, but its quicker

    http://www.youtube.com/watch?v=330Zh7vUc6k
    Thomas W.
    Euro-sport Evo, Scratch built 1/7 F-14D Tomcat, 26.5% Gee Bee R2

  3. #3
    Campy's Avatar
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    RE: Fibreglassing over Balsa


    ORIGINAL: yellowpiper

    Question for you
    I am building a 1/5th scale DHC Beaver. The entire plane is skinned in 1/16 and 1/8 balsa. I was originally going to cover her with Solartex fabric but have since thought that glassing her using water based Poly Urethane might work well.

    Does anyone have any advice on the idea and or point me in a direction or advice on how to fibreglass using water based Poly Urethane.

    Any advice or direction would be helpful.

    Colin
    Here you are....Step by step instructions.

    Glassing with Water Base Polyurethane


    1. Sand the model with 220 grit and remove any highs/lows you may find.
    Fill as needed with lightweight filler and sand.

    2. Give the wood 1 thin - medium coat of wood sealer. I use the
    commercial stuff. What this does is twofold - it stops the balsa
    from soaking up too much of the poly and at the same time protects
    the balsa from the water in the polyurethane.

    3. When dry, sand lightly with 220 to remove the "fuzzies".

    4. Some people say to apply a light coat of 3M #77 adhesive to the
    wood at this point. I have found that this is more trouble than it
    is worth since if you have a wrinkle, the complete piece of fiberglass
    has to be removed to straighten it out.

    I prefer to lay the fiberglass cloth on the part/area to be covered and
    smooth it out using a SOFT brush. Brush FROM THE CENTER TOWARDS THE
    EDGES. The static electricity usually holds it in place. I normally
    use 1/2 oz (.5 oz) or 3/4 oz (.75 oz) fiberglass cloth.

    5. Using WATER BASE polyurethane and a FOAM brush, start at the center
    and brush towards the edges of the fiberglass. All you want to do is
    stick the fiberglass to the balsa, so excessive amounts are not needed.
    Any additional pieces of fiberglass should overlap each other about
    1/2 - 3/4 inches.

    Let this dry. DO NOT SAND !!

    Brush on another coat of polyurethane. This coat can be a little heavier.

    Let this coat dry. DO NOT SAND !!


    6. Mix up some polyurethane and microballoons. I use 1 part
    microballoons to about 5 parts polyurethane. This will be on the thick
    side.

    Brush on a medium coat of this mixture and let dry.

    7. Wet sand this with 220 or 320 grit paper. BE CAREFUL, AS YOU CAN
    VERY EASILY SAND RIGHT THROUGH THE FIBERGLASS.

    8. Check the fiberglass carefully to insure the weave is filled. If
    the weave is not completely filled, repeat step 6 and 7.

    9. SPRAY a coat of water base polyurethane on the plane and let dry.
    DO NOT SAND !!

    10. Spray a THIN coat of primer on the plane. When this is COMPLETELY
    dry, block wet sand with 220 or 320 grit as much of the plane as
    possible to highlight any highs/lows you may have missed during your
    sanding/prep. The areas that can not be block sanded, CAREFULLY sand
    by hand. (TIP: CA some of the wife's/girlfriends fingernail file boards
    together. Wrap the sandpaper around them so you can block sand in tight
    areas. The CA helps prevent the boards from disintergrating in the water)
    Fill any low areas with a lightweight filler and sand when dry.

    Apply a THIN coat of polyurethane to these areas.

    When the poly is dry, repeat this step until you are satisfied that all
    the highs/lows are removed.

    11. SPRAY a thin coat of polyurethane on the plane. When dry, spray
    the primer.

    12. When the primer is dry, you can apply your rivets, panel lines and
    other detailing desired.

    13. Now you can spray your paint.




  4. #4

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    RE: Fibreglassing over Balsa

    well said campy. that's how i do it.
    David

  5. #5

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    RE: Fibreglassing over Balsa

    Thanks for the info. Very helpfull

    Question.
    How do you finish off the corners
    For example on the fuse do you start on the bottom, trim to edge and then overlap the sides on to bottom by a slight margin.
    What about the wing.




    Interesting video invertmast, thanks campy and looked at a build thread by dhal22.


  6. #6
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    RE: Fibreglassing over Balsa

    I used the WBPU method above with excellent results - it was so easy and clean. I always stayed away from glassing because the challenge to get a good light finish, but the WBPU is so easy and because the PU evaporates, it makes for a light finish.
    Steve

  7. #7

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    RE: Fibreglassing over Balsa

    Can you help me with finding a source for .05 oz cloth or even .75? I don't want to buy it one square yard at time. I used to buy it from a guy out west, but can't find him. Any help would be great.

  8. #8

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    RE: Fibreglassing over Balsa

    I use Thayercraft for most of my glass needs.

  9. #9
    Scorpion Racing's Avatar
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    RE: Fibreglassing over Balsa

    Yes, Thayercraft is a great site for glass. I just got 50 Yds. of the .75 oz. for $75 delivered along with a few other weights of cloth. Each weight was rolled on a PVC pipe, sealed in plastic and wrapped in shipping paper. Good people to deal with and very quick service.
    Scott Smith
    NMPRA 86t - District 7 VP

  10. #10
    saramos's Avatar
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    RE: Fibreglassing over Balsa


    ORIGINAL: yellowpiper

    Thanks for the info. Very helpfull

    Question.
    How do you finish off the corners
    For example on the fuse do you start on the bottom, trim to edge and then overlap the sides on to bottom by a slight margin.
    What about the wing.

    I would recommend proceeding back to front, and bottom to top. For example, if you glass the fuse, start on the back and work forward. this way, all overlaps are backward facing. On the wings, do the bottoms first with a little overlap onto the top of the wing along the leading edge. Then do the top of the wing overlapping onto the bottom along the leading edge. The overlaps do not need to be too large, 1/2 to 1 inch, but this will also give two layers over the leading edge for a little more hanger rash resistance. Same with the hoirizontal stabs. Trailing edges are usually too sharp to bend around and are typically sanded once cured to trim the overhang.

    Scott

  11. #11

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    RE: Fibreglassing over Balsa

    I personally wouldn't use water base anything.
    Owner: CFC Graphics. "Model Airplane Graphics from a Model Airplane Builder." cfcgraphics.com

  12. #12

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    RE: Fibreglassing over Balsa


    ORIGINAL: Avaiojet

    I personally wouldn't use water base anything.
    Charles, the water based polyurethane provided an excellent surface for your graphics on my MK Blue Angel. But I think the automotive clear coat will help with the concerns you are thinking about.
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    David

  13. #13
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    RE: Fibreglassing over Balsa

    I started modeliong in 1975 and have used epoxy & glass. I've been away from the hobby for some time now and am currious agout the WBPU process. This thread has been very informative so far. My next project will be a 20% scale Zlin 526

    At this point my only question is, whis PU product seems to be the poupular one to use?

    Thanks!

    Ken

    OK I lied ..... I do have another question. Is the surface of a WBPU as hard and tough as a surface done using epoxy?
    Sent from my Dry-Erase-Board

  14. #14

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    RE: Fibreglassing over Balsa

    Which PU product seems to be the popular one to use?

    Most use Minwax Polycryilc.

    Is the surface of a WBPU as hard and tough as a surface done using epoxy?

    No it is not as hard as epoxy, but it is lighter and reasonably hard.


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