I had a feeling that might be the case, I'll have to take my begging bowl and a few sacks down to the nearest coal power station and see if I can get any spare fly ash that drops off the transport.
Whilst I typed this I had a flash back to my youth, when the less well off used to go down to the coal merchant and collect by the bucket full what basically we called coal dust /slag for free (if he wasn't around) from the merchant. We often used it to bank up the fire overnight, so there would still be embers to start the fire next morning. Those were the days when as kids we were tasked with counting the coal bags the coal man emptied into our coal store, he was not the most reliable with his count or weighing of coal bags, living in a massive house in what was known as millionaires row some distance away in Tettenhall Rock........I never met a poor coal merchant.
Oh so much simpler times.