Bonding new concrete to old concrete

Discussion in 'Builders' Talk' started by sparky64, Jun 3, 2021.

  1. sparky64

    sparky64 Member

    I have trenched across a concrete drive to install below ground rainwater drainage, we are not on mains drains and have soak aways for rain water run off from roofs.

    I now need approx 0.5 cubic meters of concrete, but how do i ensure it bonds to the existing concrete? what preparation should i do on the existing concrete?

    what's the average cost of ready mixed concrete?

    Thanks for any responses.

  2. DIYDave.

    DIYDave. Screwfix Select

    To improve bond between old and new concrete /

    Brush away loose material

    Prime edges of trench with SBR, diluted as per instructions on tub

    Don’t use PVA - looks similar to SBR but different beasts - use SBR !

    As for costs - no idea
  3. sparky64

    sparky64 Member

    Thanks DIYDave
  4. stuart44

    stuart44 Screwfix Select

    For a bonding mix, use cement with the SBR and brush it on the edges, but you then need the concrete placed within 20 minutes.
  5. stevie22

    stevie22 Screwfix Select

    Soak the concrete for a few hours before you start. Mix a little cement and water to a slurry and paint that on. You don't need fancy chemicals.

    Keep the concrete nice and stiff find a mobile batch plant rather than the traditional spinner truck.
  6. sparky64

    sparky64 Member

    Thanks for the replies guys.

    The average quote for 1 cubic meter, that's the minimum they will deliver, is £175. At the minute there is a shortage of concrete and so costs have gone up.

    I'm not sure what a mobile batch plant is, but i'll certainly do a google :)
  7. stevie22

    stevie22 Screwfix Select

    It's a Ronseal job (just what it says). The truck carries aggregate and cement and produces the mix you want on the spot in the exact quantity and the exact workability.
  8. sparky64

    sparky64 Member

    I got a mobile batch plant in the end, thanks for the info.

    There is a little bit where the new concrete hasn't bonded to the old concrete, i did the job on a hot day earlier this week and think that the slurry must have dried before i got to this area to level out and smooth off.

    What would you recommend i do to repair, or should i just leave it alone? will it get worse in the winter?


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