I have removed the leaking, ancient, shower tray from a bathroom to
discover a large concrete block beneath it, ringed with brick. The
underlying floor is concrete slab, it's a ground floor.

http://picasaweb.google.co.uk/TheOld...eat=directlink

I would like to drop the height of the shower pan when I replace it.
This is because of the limited clearance above because of the
load-bearing lintel above (this was the garage door before an ancient
conversion.) There will be just 1850mm between the top of a
low-profile shower tray if I put it on the concrete.

The alternative is to use a 900mm tray with a 760mm door, and build a
false wall for the left hand side. (You can see - line of silicone &
marks on the floor tiles - where the imbecile that did the original
work built such a false wall - on the the WRONG side!)

I'll need about 90mm below the tray for a trap, this will just leave
enough to get through the wall to a gully. It's all horribly tight.

Now. How do I get the concrete out? I've thought:

1) Hire a breaker - but I don't want to damage the underfloor, or the
drain the runs right under.

2) Drill many holes with SDS+ and then take it out in chunks.

3) Drill and cut at the parting line and then drive a chisel in with a
sledge. I'm not sure if it will part with the floor though.

4) Some other idea that I'm too thick to have thought of.

I'd welcome ideas. (I only have a 115mm Angle Grinder though).

R.