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Thread: flat roof

  1. #1
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    flat roof

    Ado there,
    Just a quick one, as im struggling to obtain osb interlocking boards
    around here, i will be using the osb 3 8x4 sheets. Now, i am covering in two
    layers of 450 fibreglass, but do i still need to bandage the butt joints?
    Many thanks..

  2. #2
    Super Moderator Alex's Avatar
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    Officially I would say yes. But 2 layers is strong enough to sort expansion stress, the only thing is too make sure all the gaps (3-5mm between boards) dont fill with resin. Dare I say very thin masking tape.

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    Many thanks, I see where your coming from. Alternatively I might try foam tape between the joints for expansion, so no resin seeps in joints
    then apply two layers of 600gsm, for peace of mind...

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    For anybody else looking at this then you should always support the joints of square edge boards with noggins.

    I have renewed a number of roofs whereby builders have taped joints with duck tape. This is a NO,NO!

    Let the resin seep between the gaps to form the bond. Tape if 600csm or less with GRP bandage.
    Last edited by Alex; 07-12-2015 at 10:12. Reason: Removed advertising line

  5. #5
    Super Moderator Alex's Avatar
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    Quote Originally Posted by Fibretechs View Post
    For anybody else looking at this then you should always support the joints of square edge boards with noggins.

    I have renewed a number of roofs whereby builders have taped joints with duck tape. This is a NO,NO!

    Let the resin seep between the gaps to form the bond. Tape if 600csm or less with GRP bandage.
    That applies fine for T&G (although you wouldn't tape the joints at all). BUT.....
    this post regards cut edge boards, and they do require a 5mm expansion gap between them that must be left empty.
    Last edited by Alex; 07-12-2015 at 10:15. Reason: grrr...spelling

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    Expansion

    On three sheets of conditioned 2400x1200 I would not consider expansion gaps are necessary....

  7. #7
    Super Moderator Alex's Avatar
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    You carry on but wood is going to move. They have a completely rigid, fully bonded fibreglass coating on them remember. I have seen many, many roofs where you can see board edge peaks. Touching boards do eventually create ridges to appear which is unsightly at best, on a LARGE roof this can cause stress on the fibreglass and also possibly start a release between the fibreglass and decking. Not only that the slight squeeze on the boards can make a loud noise during heating and cooling cycle during the day / night. What I say might be overkill but there are so many variables (room moisture, wood moisture content, temperature, fixtures, wood defects) why risk it, it's such a small job and not leaving expansion gaps, even on a small roof, is lazy.

    Or look harder for 8x2 T&G.

    Wait.....this thread is 18 months old, I think he's probably done by now.

    /Rant over, back to sleep.
    Last edited by Alex; 08-12-2015 at 10:17. Reason: Not the droids i was looking for.

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    Lol - Alex you are the fountain of all knowledge and have helped me out in many a situation with good sound advice - it is why we only use T&G.

    No point in looking for the larger boards, you just need a good supplier for the small 600. They are lighter and you ultimalty end up with less waste. I can get two 600 boards cheaper than one 1200 straight edge anyhow.

    Can you advise though for others - how you leave this unbonded 5mm gap - I would assume that when you wet out the board, fit your bandage, wet out again and consolidate that the 5mm gap is full to the brim with resin?


    This is a review I left for you in 2014....and it still stands - ain't had no biscuits lately with me order though.....

    https://www.yell.com/biz/cfs-fibregl...edruth-112210/

    Regards

    Drew @ Fibretechs

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    reading backwards the advice is masking tape....think this should really read - do not use square edge - T&G ONLY

    Drew
    Last edited by Fibretechs; 08-12-2015 at 16:37.

  10. #10
    Super Moderator Alex's Avatar
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    yes masking tape is ok, I am not a big fan though. It's better too use the woven fibreglass tape, put it down dry and paint the back with some resin till it goes clear. It works as joint reinforcement too, if you were too scrimp on cost and only use 1 layer 450g, which we wouldn't dream of doing.

    Ross said, you should cut down on the biscuits!
    Last edited by Alex; 08-12-2015 at 17:19. Reason: My lack of faith is disturbing

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