Renovating a stone building in the Banbury area is mostly a matter of undoing what somebody helpful did to it in the 1970s.
Local ironstone is soft and porous, and it was built to handle water by absorbing it and letting it evaporate away again. The lime mortar around it was deliberately softer than the stone, so that any movement or salt damage happened in the joint, which is cheap to replace, rather than in the stone, which is not.
Cement pointing reverses that completely. The joint becomes harder than the stone, water that gets in cannot get out through the mortar, and it leaves through the face of the stone instead, taking the surface with it. The result is the crumbling, spalling stonework people ring us about, and it is almost always a consequence of the repair rather than of the weather.
The same applies to coatings. Any impermeable paint or sealer on ironstone traps moisture behind it and accelerates exactly the decay it was sold to prevent. There is no product that fixes a damp stone wall by sealing it.
Doing it properly means raking out cement carefully without damaging the arrises, repointing in a lime mix matched to the stone, and accepting that it is slower work than the job that caused the problem. We will also tell you honestly where pointing does not need touching at all, which on stone is more often than people expect. More on our renovation and refurbishment page.