On Sun, 01 Apr 2018 19:12:40 +0100 (BST)
"Dave Liquorice" wrote:

What would be the best method to get white emulsion off rough split
sandstone and the mortar (cement not lime) joints? The wanted end
result being visible clean stone and mortar. There is only about 1 sq
metre to do, indoors.

Thinking of a steam cleaner to soften the paint but how to remove the
softened paint totally from the gain of the stone? Indoors, so
sloshing lots of water about isn't on.

I'd try a test patch with caustic soda and a scrubbing brush.

Mechanical with a needle gun?

That's a good way of removing heavy scale from steel ...