How old is the house ? if it was built within the last 30-40 years it is more than likely that the internal skin will be Breeze block, not very nice to look at, if it is an older house it is a job you could do yourself, but it is dusty work, if you not used to using kangos, I would say do it with a club hammer and Bolster chisel, it will take you ages unless the mortar is quite soft, then you will have to have brisks cleaned and probably re-pointed, I would get a quote from a builder first.