The mò reading is the building-trade word - used when mortar, plaster, or filler is spread on a vertical or rough surface. Key collocations:
抹墙 (plaster a wall),
抹平 (smooth over),
抹灰 (apply plaster). It also shows up in the idiom
拐弯抹角 (beat around the bush - literally 'turn corners, skirt angles').