in page oil tank after lifting paving blocks and finding void under concrete raft supporting oil tank.
Decisions and implementation:
Has been deliberately made that way for a reason. So can easily gain access to the "4inch" (large) soil-pipe if needed - can dig out and access without disturbing oil tank.
But do seal the void - deny as start of route into house for unwelcome visitors - rodents, etc.
"Sealing rat hole wall and pipe-riser"
in wall of house.
This is an earlier-stage outside-location layer of defence.
Use masoned pieces of broken-up concrete paving from another task to make one quite well-fitting layer "just" under the raft.
Easy to remove in future if need access under oil tank raft. Obvious to see what it is.
Purpose is to form a dam-wall retaining concrete to become base for paving blocks.
Ballast (sand and gravel mix) with cement for strong mix which also doesn't freely flow in gravity.
Concrete level matches base level of existing paving.
This has the effect that the paving concrete base comes part-way up
the concrete raft - so making a seal. No access to the void region
under the oil tank raft.
As seen in the photos of the concrete paving block base.
Blocks in-place. Replaced in previous arrangement. Some slight trimming called-for, but mainly matching and placing.
Done. Small amount of sand-and-cement mortar poured into spaces
between blocks in near part of view. To make good the seal.
Cut pieces of plastic sheet used to ensure mortar cannot bond to blocks where want to leave separable butting surfaces.
Sand - builder's sand (not sharp sand nor fine paving sand) brushed and trowelled into any gaps large enough to receive that sand. Seal gaps and make block paving rigid.
(R. Smith, 29Sep2023)