Thumbkin is fine. Thanks for your comments. I must be a glutton for punishment as I have been carving more foam (but doing it very carefully).
I was going to use paper mache for the stove surround, but there is something very satisfying about carving builder's foam. I have some cool dental tools which are fun to use. I sketch out roughly what I want with a pen and then carve in the details. I have been making fireplaces for both Dr Zoe and Fairy Hazel.
The foam actually takes paint quite well. I have used this method before to make a base for my Greenleaf Tennyson (even though a Newberg dollhouse is currently sitting on top of it).
The only problem is that it chips very easily and then you can see the blue foam.
This is not a good method for a dollhouse base, whereas the paper mache rocks on the exterior of the Westville are set like concrete and are extremely difficult to damage.
Dr Zoe and I decided to just go with the foam rocks over and around the stove. (As Dr Zoe pointed out, she will not be bumping them like the clumsy human does!)
It seems quite obvious that she has also consulted with Harley (the Tree Ent) as her house is beginning to have tree branches/roots taking over. I guess that she also wants a tree-house home.