Constructional Hearth
 

I'm new to DIY. I have removed an old surround and the fireback etc to
open up the fireplace to fit a stove. The only problem is that the
constructional hearth is crumbling and is in a state of poor repair
generally. I think it is probably better to replace it. How do I go
about it?

Constructional Hearth
 

Hard to say with information given. Usually jack hammer the beast out
and replace. Is it cement, tile, marble etc...