On Sun, 22 Aug 2010 02:44:45 +0100, Tim Watts wrote:

For cleaning/decorating, it's not too much trouble to whip out a bit of
hardboard, and it should be perfectly feasible to move it into the hall
with 3-4 boards.

I don't think you'll find hardboard will work particulary well for a
piano, they are damn sight heavier than a washing machine. Also any
small bits of grit caught between the hardboard and floor will make
some lovely scratches... I think you'll also need something thick
enough to raise the piano off its wheels and spread the load over as
much of the base area as possible. Working on the basis that friction
between two surfaces is a function of the load pressing them
together.

How about a bit of ply (15mm?) and thick carpet glued firmly
together? Carpet back to ply, use with pile side against the slate
floor. You may need something noslip on the other side of the ply to
stop the piano sliding on the ply and include some large handles in
the sides/ends of the ply so you can push pull it with a rope rather
than shove on the piano.

Got to be 1/4 ton or more in all.

At least... how often do you intend to move the piano? Generally
speaking they don't like being moved as it messes up the tuning, same
for the enviroment they are in they like a steady temp and humidity.

Re the castor cups - do you think they'd work on slate? I can see them
(assuming they are plastic) getting ground away in pretty short order.

Again hard so any grit will make a nice grinding paste... You might
get away with felt pads on the bottom of castor cups. They would be
good for felt based ones would be good for spreading the load when
the piano is in posisition without raising it up 3"...

--
Cheers
Dave.