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Helical bar for lintel - 6mm or 8mm?

Discussion in 'Building' started by nic11, 4 Jun 2019.

  1. nic11

    nic11

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    Hi,

    Trying to determine whether I should use 6mm or 8mm bars to create a lintel repair above a patio door. I had thought 8mm, but since read that thicker isn't always better for crack stitching because of flexibility.

    The house I bought 4 years ago has two cracks at the back, one stepped crack from the kitchen window and another from the patio door. It's a 1930's semi with cavity walls. Windows and doors were replaced circa 15-20 years ago by previous owners and 11 years ago they some remedial wall-tie work done and at some point an attempted repair on the crack above the patio door was done (simply filled the crack in with mortar!). The upper half of walls are rendered in concrete The crack above the kitchen window was under 1mm and the one over the patio door about 3mm.

    At the time of purchase the advice was to get it repaired but get further advice from a structural engineer if their was any further movement. The cracks have not changed in 4 years and are only in the outer wall. I have used 6mm helical bar to repair the kitchen window crack a few months ago - two rows of 3m bars 3 courses apart to create a brick lintel and then using 1m bars 6 courses up where the crack extends to. Easier to do the smaller one to practice/fine tune what to do :)

    The patio door is 2.2M wide so going to use 7M bars cut in half. Not sure whether to go for 8mm bars because of the wider opening or simply stick with 6mm - contacted the company who gave me Load tables for the bars, which is only useful if I can work out the load, or if I need to.
     
  2. noseall

    noseall

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    I'm not sure how you can successfully repair a concrete (in-situ) lintel with helical bars. The downforce in the middle of 2.2m wide opening is not going to be resisted by a few screwed in bars. You may actually make things worse.
     
  3. Notch7

    Notch7

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    Im guessing the helical bars will go in the brick mortar joints?

    I know some builders fit steel bars before forming an enlarged opening to help stop cracking of brickwork during the process of making the opening
     
  4. nic11

    nic11

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    Helical bars are used for remedial crack stitching as opposed to removing bricks and feathering back in. There is no concrete Lintel to disturb its the external brickwork, the bars go in the mortar joints. Cracks occur as uPVC does not give same support as original wooden windows

    Got further clarification from a technical expert - double 6mm bars have a tension load of 16kN and double 8mm bars have of 17.6kN, and for my 1930's semi the 6mm are fine - he gave the proviso of unless the mortar joint is 14mm in which case the 8mm is advised.

    Thanks for the replies, just thought I'd post after getting further advice :)
     
  5. ^woody^

    ^woody^

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    I'm sure nosey knew all that really and is aware of all this modern building malarky :rolleyes:
     
  6. noseall

    noseall

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    My 'thank you' telegram should reach you by morning.(y)
     
  7. John D v2.0

    John D v2.0

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    Not used that app before is it any good?
     
  8. noseall

    noseall

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    More reliable than pigeon or smoke. I'm no luddite.
     
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  9. tony1851

    tony1851

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    Are the bars stainless steel? Using ordinary mild steel in an outer skin might cause problems.
    Are they being fitted in mortar or epoxy?The crack-stiching kits usually recommend epoxy bedding finished with mortarpointing.
     
  10. nic11

    nic11

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    Yes, stainless steel grade 304 with an polymer resin grout designed for use with the helical bars. The grout bonds the bars and the steel together and is non-corrosive, non-gaseous.
     
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  11. scbk

    scbk

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    Was just hearing today, that they plan on repairing this crack with helicoil bars



    [​IMG]
     
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  12. trevorbayliss

    trevorbayliss

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    I am doing the same thing at the moment. Smaller window openings.

    2 x 6mm H bars in the joint and you use 2 joints. So 4 pieces needed in total.

    I was told you need to go past the window by 500mm each side. So you will need longer lengths.

    I bought 2 x 10m coils on ebay for £90
     
  13. nic11

    nic11

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    Opening 2.2M + 500mm each side is 3.2M
    7M lengths cut in half is 3.5M

    were the coils from ebay good quality? Who were they from?
     
    Last edited: 6 Jun 2019
  14. trevorbayliss

    trevorbayliss

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    Oh yes that’s right, must of read it wrong.

    Yes good quality and from a company who use it to repair bricks/cavity ties etc.

    They must sell a bit on ebay for extra income. Have a look and you will only find one supplier on there doing the longer coils.

    How much were yours?
     
  15. nic11

    nic11

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    So it's the one supplier doing the 10m coils?

    I used permagard, a kit for £90 plus got some 3m lengths for Window. The 7m only comes in 5 pack which is £132 so might consider the 10m coil as I would have only needed 2 lengths. Still have enough resin from first job.
     
    Last edited: 6 Jun 2019
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