On Mon, 2 Apr 2018 00:08:11 -0700 (PDT), harry wrote:

And a manual brush at that, I suspect that a cup or disk brush on
an
angle grinder may leave unsightly swirls.

I lived in a sandstone building many years ago. A finger nail was
enough to cause plenty of surface damage.

It depends on the sandstone.
It can be soft as **** or really hard.

There are two types kicking about around here, both are fairly hard.
One is moderately coarse and when exposed to the weather for a bit
will split very easyly (aka fall apart) along a bedding plane. The
other is much finer, harder and of "engineeering" grade.

The hardest sandstone is in the North of England

http://alstonnaturalstone.com/index.html

This is the fine hard stuff, has nice colour variation.

--
Cheers
Dave.