I'm sorry I don't have the original thread to respond to but I wanted to add
a few comments on removal techniques to the other messages.  While speed is
crucial in removals good practice helps too.  Even water borne paints become
insoluble in water after drying.  If re-dissolved by using solvent strippers
while still fresh they can, particularly if the paints include dyes, spread
into the porous underlying stone.  It is important to pre-wet the stone to
the saturation point before applying the stripper to reduce the likelihood
of leaving a shadow.  The water reduces the effectiveness of the stripper
and multiple applications can be required.  Low pressure water rinsing
between applications is called for but be careful of etching the sandstone
by impatient technicians with pressure washers, (see wood shingles).
Alkaline paint removers can be more effective and do not produce shadows but
are nasty to work with, take a long time, and can induce iron staining in
certain sandstones.  Best to test procedures in small areas first before
applying all over.

Good luck.
Mark