I've been asked to remove some slate floor tiles in a massive kitchen.

They seem to be laid on a layer of plywood or possibly blockboard which
is in turn laid onto the original floorboards.

The owners want to salvage as many as possible so the can sell them.
The tiles are about 20mm thick.

Questions:

1. How do I remove them
2. Will they come off whole or are they more likely to break

I'm thinking of doing it by levering my massive crowbar under the
blockboard/plywood layer to loosen than in the hope that the flexing of
the layer will break the bond between the tiles and the blockboard
layer.

Any tips would be appreciated.