Does fine, pure graphite block electromagnetic waves like aluminium or other conductive metals?

It depends on the wavelength you want to block and the thickness of the material, but yes it can. Just not quite as well as materials with higher condivtivity.

It depends on the wavelength you want to block and the thickness of the material, but yes it can. Just not quite as well as materials with higher condivtivity.

could it be used in a garden shed to block sound aswell as electromagnetic waves?

graphite tends not to be very good at it because it will conduct fine in one direction but not very well in another, this is due to the lattice structure of the graphite.

 

also, its sound absorbing properties would not be very good i would imagine.