Hi Maggie,
I have done various courses at Prochem, who supply cleaning chemicals to the cleaning and carpet cleaning companies.
If you were to go onto their web site:
www.prochem.co.uk and click onto "contacts", then click onto "Training and Technical", you can email your query giving as much info as you can about the limestone not forgetting it is on the wall and not on the floor, and next to the sinks etc etc, they will come back to you with the product needed and also the best way of doing the job, protection, seals etc. Better mention that you need a speedy response if you are doing it today!!
Most of the products they recommend can be applied by low pressure sprayer, brush, cloths etc
Failing that, your local cleaning supplier should be able to guide you in the correct procedure for doing the above. I have always found my cleaning supplier to be a wealth of experience, help and guidence.
As always....
Tim