Answered on 26th Feb 2019 - Member since Mar 2019 - report
You would have two main options available to you for repairing the damage to the stonework.
The higher quality option is to use a repair filler with some suitable stone that matches your walls, while the cheaper option is to use mortar repairs.
For repair filler a popular choice is Litho-Max, which is easiest found online these days, and you can find matching stone from stone merchants or even salvage merchants. (You may also want to consider dye powder if you want to get the colour to be an exact match.)
As this is Bath stone, you should find it reasonably straightforward to chisel the stone as it is quite a soft stone – but if you are unfamiliar with this, this may be where you would prefer a stoneworker to do this for you.
Generally speaking, natural stone repairs will be best for the value of your house in the long-term and without some of the risks of mortar repairs.
Mortar repairs will be quite cheap and convenient enough to do yourself, however it is more difficult to get a matching texture or colour, which may not be ideal if you ever plan to sell your property. Additionally, the mortar will be porous which means it can hold water – this may be problematic in cold or icy weather where this can cause the mortar to crack and cause further damage. In some cases, this could cause leaks to the inside of the home.
Generally, I would recommend the option of using a repair filler (specifically Litho-Max) and to source some Bath stone that is local to you. If there is any of the work that you are not sure about, I would recommend to seek advise from, or hire, a local stoneworker to you. "