you got to scrap off the paris white layer around the crack down to the dark layer about six inches wide then carve out the crack in the dark layer. then you screw washers to lath and patch the base plaster with the mesh and let it dry for a week. then you put the paris white layer all over smooth and let it dry for over a month before you paint. if you put the mesh tape on top of or in the paris layer the crack will just come back in the winter. oh and you might need bonding agent. we have earth and hair base plaster so we couldnt use bonding agent instead we used something called hyde glue wash because bonding agent would melt the earth hair plaster.