I want to support my ground floor joists. This is partly to take the
weight of a piano and also because the joists do deflect rather a lot
anyway when weight is put on them (such as bookcases, cookers etc.
The joists in these houses (8"x2" at 18" centres) are, apparently, of
rather poor quality and have shrunk and bent in every house in eth
development. They were built in 1964 - part of the "Span House"
movement. When the floor deflects the walls that are built on it (of
block) move and crack which is not nice.

Under the house the gap between the earth to underside of each joist
is about 50cm. This is too big for a car scissor jack - I had
imagined using a row of scissor jacks. It's too small for an ACROW
prop.

One simple solution is to use some wooden 4"x2" props with carpenter's
wedges to adjust the height. But I am worried about creating a damp-
conducting path up to the joists even if I stand the base on damp
proofing membrane.

Does anyone have any other suggestions?

Robert