Where is the DPM at the moment?
100 years old may not have a DPM.
It's just that if the DPM was underneath the concrete, then you would want to put it back there, not on top. Otherwise it's as per your original plan - apart from the mortar bit - it should be screed or sharp sand, not building sand which is in mortar.
Make sure to compact the fill so that it doesn't settle and drop. And presumably the water pipe had been insulated for the vertical 700mm or so?
pack up to conc height an then drop down a square of plastic, as a local membrane, fill with semi-dry conc, mix it youself and tamp down. cut the flopping edges of the plastic just beloww ffl.
idealy it would be best to glue the membrane to the 110mm upstand pipe but just do the best you can. the job looks good from here
no. dpc is wrong material an bitumen aint needed.
rip open a hefty rubble bag or cadge an off-cut of DPM sheet membrane to use as a membrane under the concrete. your usingthe plastic sheeting to form a bag with a hole for the 110mm pipe in the middle
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