Patio extension - Requirements to extend base

[NewForestLodger]

Hi all, great site........ I am looking to extend an existing patio. I have taken up the existing slabs which were laid with the dreaded spotting technique on solid concrete,which is still sound. I will be extending the patio out by 3 metres, which is the best method for the sub base ect.. ie.. would I need to extend the base with solid concrete? Any advise would be gratefully received!!

[TheVictorianCobbleCo]

Short answer - either remove the existing concrete base or extend, don't leave the concrete and then add crush/sand/compaction. The difference in expansion/contraction/movement will give a lovely crack along the joint line of the new patio.

[NewForestLodger]

Short answer - either remove the existing concrete base or extend, don't leave the concrete and then add crush/sand/compaction. The difference in expansion/contraction/movement will give a lovely crack along the joint line of the new patio.

Many thanks 'TheVictorianCobbleCo'.I will extend the existing base with concrete,would I need to incorporate some sort of expansion joint between the new and the old or just concrete up to the old base?
Thanks In advance....

[TheVictorianCobbleCo]

Possibly the best is to drill horizontally 10mm dia at least 100mm into the existing slab, assuming it is thicker than 75mm at half the thickness (i.e. 37,5mm, but I'm assuming your slab is at least 100mm thick, giving 50mm in the middle) doing this every 600mm or so, then cut 10mm threaded bar 200 - 300mm long and bang these into the holes. The rod must be a tight fit in the hole. Make sure your new base is properly compacted and then throw you r new concrete. The bars effectively control the vertical movement. Which is what you need. Horizontal movement is not an issue. If you cant do this, or the slab is thinner than 75mm make absolutely sure of a good subbase and wacker it at least 8 passes, and cast up to the existing slab. I generally use expansion joints if my slab is bigger than 3m x 5m, and the slab is 75 to 100mm thick.
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Good Luck