In article , "Luke"
says...

Has anyone tried using diluted white wood glue as a stabiliser
solution for powdery old mortar? When I am drilling to install wall
plugs in an old brick wall built with lime mortar, and hit a joint, if
I don;t have the option of drilling in a diferent place, I usually
scrape away a lot of the loose mortar in the joint I've hit, blow all
the dust out thenand squirt in some stabilizer solution. Then when
it's dry, I pack the hole with polyfilla or cement mortar and later
drill a proper small hole to take the plug. In the absexence of
proprietory stabiliser solution, I often wonder if diluted white wood
glue would work OK. Has anyone tried that?

Haven't tried it, but don't see why it wouldn't work. I sometimes
stick the plug in at the same time as the filler, so there's less
chance of dislodging anything by drilling later.