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Polyurethane wood glue instead of chemical fixing for thermalite blocks?

Discussion in 'Building' started by ^woody^, 19 Jul 2018.

  1. ^woody^

    ^woody^

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    I need to fix a very heavy floating shelf into a thermalite block wall and the three different fixings I’ve tried are crap.

    It occurred to me that polyurethane wood glue expands quite a bit when drying, and as I have some, and it does say it sticks other materials not just wood, I wondered if it would do the same job as resin anchor fixings and give a nice tight grip to threaded rod.

    Has anyone had this brainwave previously? And more importantly, is whatever you stuck up, still up? :cautious:
     
  2. Notch7

    Notch7

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    Tests using PU glue for timber joints show a considerable reduction in strength when the joint is 'gappy', so in that application, its foaming gap filling nature dont actually mean it is suitable for gap fillling applications.

    your application is different though because the strength relies on the rod staying in the hole by the glues adhesion to the hole and rod. There isnt any shear strength needed, the rod is resting against the block.

    My concern I suppose would be the density when dried. The resin is a 2 pack epoxy and sets pretty hard.

    AFAIK PU requires moisture for curing, hence fine in wood, not sure about a very dry internal block.

    I havent tried it in practice so, but Id be interested to know as well!

    Are you too mean to buy a resin kit then?, or dont have the twin gun.....:mrgreen:
     
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  3. ^woody^

    ^woody^

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    Both :rolleyes:
    If need be, I'd get one that fits in a normal mastic gun, but I've only got 5 bolts to fix.

    My thinking is that the issue is the bolts rotating due to the soft block and the air pores, not so much the block strength. Now, whilst a proper chemical resin may set harder, it will only set harder in the block pores right next to the bolt - it can't go any further outwards into the block.

    This would be no different to using the polyurethane - it will enter the same pores and give the same amount of grip. So, as hardness of set is not the issue, the polyurethane should provide the same amount of grip in the block and prevent the bolt pulling out just the same.

    I could dampen the holes first, oh err missus.
     
  4. Nozzle

    Nozzle

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    Use the proper chemical fixing, it's way way harder than PU glue. Important to rough up the hole a bit after you've drilled it, and blow the dust clear out. The PU gorilla glue is a bit squishy, chemical fixing is hard as nails. On account of being 2 pack it is superior.

    Nozzle
     
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  5. geraldthehamster

    geraldthehamster

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    PU glue has little or no strength. I've been able to knock PU-glued timber joints apart weeks after they were glued. I'd use a proper resin.
     
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  6. ^woody^

    ^woody^

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    Yes, but in this situation, strength is not the issue - I'd argue that the glue is actually stronger than the areated block around it anyway.

    The issue is that of friction, of stopping the bolt sliding outwards, and I can't see why the PU glue would not perform exactly the same as any chemical fixing in this instance with this type of block.
     
  7. geraldthehamster

    geraldthehamster

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    I don't think it will stop the bolt pulling out.
     
  8. Chud

    Chud

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    Lidl have got araldite sized syringes of polyester filler in at the moment if you just need a bit - to be honest I think you'd be better off whanging a load of nemesis/sticks like sh*t/pinkgrip solvent free in the hole and pushing the rod into that - It'll have more strength than PU glue. If the thermalite is an issue you could always douse it in stabilising solution etc first...?
     
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  9. 23vc

    23vc

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    I’ve always thought dried weetabix should make an amazing adhesive, considering how I’ve almost had to resort to a belt sander to get it off the table after the kids breakfast.
     
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  10. John D v2.0

    John D v2.0

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    Trouble is it's water soluble so damp would be a disaster:LOL:
     
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  11. pilsbury

    pilsbury

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    Cheerios are harder.

    Full of daft ideas, my thoughts are as follows: breeze blocks are made of cheese. Therefore as I see it you are simply trying to stop the fixing/threaded bar pulling out of the hole. Why not drill your hole a bit smaller and carefully lever the bit up and down to make the hole wider at the back. Then drill your correct sized hole at the front. Then bung a load of pink grip in and stuff your bar in. Pink grip sets hard and will likely be firmer than breeze block. Plus now you have a big thick rod with a bulging pink tip :sneaky:
     
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  12. catlad

    catlad

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    I have used everbuild anchor set in the past and that has worked, it fits a normal gun and its less than a tenner! their is a red and green one depending what you need it for.
    I have stuck all sorts with expanding foam and it seems to stick anything, the other day I had some 4' ish lengths of batons left and I squirted a bit of foam on the end and overlapped the batons by 6" and then clamped them together.
    The next day we could not pull or twist them apart.
     
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