On Tue, 20 May 2008 17:44:37 +0100, stuart noble wrote:

How much does this piano weigh? A Yamaha grand is only 250kgs. Ten bags
of sand isn't going to do much to any floor.

Not if you spread 'em out but pile 'em all in a heap at one side... The OP
has already stated the the floor and walls move enough to cause cracking
in normal use. 8 x 2 at 18" is, IMHO, a pretty light weight bouncy floor.
10 x 3 at 12 would be a good strong a floor.

--
Cheers
Dave.