Dominic-Luc Webb wrote:
Hi,

I am not sure what fly-ash is chemically. What kind of
power station would have this?

Hi Dominic,

Its a by-product of coal power stations.

Many "Thermal" building blocks are made of it - it is mixed with cement
and aluminium powder, water is added, and then the aluminium reacts with
the water and alkali to produce hydrogen which bubbles the cement to
make a very lightweight concrete.

You could conceivably powder such blocks if you broke them up in a
concrete mixer.

You can also buy silica "flour", glass microspheres etc as fillers for
fibre glass work (look at "West system" epoxy for example for fillers)

Steve