Mixing machine (10, 110, 210) for the preparation of mortars and plasters for the construction industry, comprising: - a loading tank (11, 111), in turn comprising a loading mouth (12, 112), one or more inclined walls (13, 113), and a bottom (14, 114) towards which said one or more inclined walls (13, 113) converge; - a tubular mixing chamber (15, 115, 215), in turn comprising an inlet opening (16, 116) connected to said loading tank (11, 111), an inner surface (22, 122, 222), and an unloading mouth (17, 117) positioned on the opposite side of said tubular mixing chamber (15, 115, 215) with respect to said inlet opening (16, 116); - a feed screw (18, 118, 218), rotatable about a feed axis, configured to determine the movement of a material to be mixed from said bottom (14, 114) of said loading tank (11, 111) towards said tubular mixing chamber (15, 115, 215); - a mixing tool (19, 119, 219, 319, 419, 519), placed to operate inside said tubular mixing chamber (15, 115, 215) and operationally connected to said feed screw (18, 118, 218) so as to rotate with it; - pumping means (20, 120) for introducing a mixing liquid into said tubular mixing chamber (15, 115, 215); - drive means (21, 121) for driving said feed screw (18, 118, 218) and said mixing tool (19, 119, 219, 319, 419, 519), said mixing tool (19, 119, 219, 319, 419, 519) comprising a rotating longitudinal body (25, 125, 225, 325, 425, 525) placed to rotate about a longitudinal axis thereof, at least one flexible scraping element (26, 126, 226, 326, 426, 526a, 526b) developing from said rotating longitudinal body (25, 125, 225, 325, 425, 525) configured to be in contact with said inner surface (22, 122, 222) of said tubular mixing chamber (15, 115, 215) at least when said rotating longitudinal body (25, 125, 225, 325, 425, 525) rotates about said longitudinal axis thereof, said at least one flexible scraping element (26, 126, 226, 326, 426, 526a, 526b) developing in the direction of said longitudinal axis between two connection points (28, 29; 128, 129; 228, 229; 328, 329) with said rotating longitudinal body (25, 125, 225, 325, 425, 525), characterized in that said at least one flexible scraping element (26, 126, 226, 326, 426, 526a, 526b) comprises a cable made of metallic material (27, 127, 227, 327, 427). - a loading tank (11, 111), in turn comprising a loading mouth (12, 112), one or more inclined walls (13, 113), and a bottom (14, 114) towards which said one or more inclined walls (13, 113) converge; - a tubular mixing chamber (15, 115, 215), in turn comprising an inlet opening (16, 116) connected to said loading tank (11, 111), an inner surface (22, 122, 222), and an unloading mouth (17, 117) positioned on the opposite side of said tubular mixing chamber (15, 115, 215) with respect to said inlet opening (16, 116); - a feed screw (18, 118, 218), rotatable about a feed axis, configured to determine the movement of a material to be mixed from said bottom (14, 114) of said loading tank (11, 111) towards said tubular mixing chamber (15, 115, 215); - a mixing tool (19, 119, 219, 319, 419, 519), placed to operate inside said tubular mixing chamber (15, 115, 215) and operationally connected to said feed screw (18, 118, 218) so as to rotate with it; - pumping means (20, 120) for introducing a mixing liquid into said tubular mixing chamber (15, 115, 215); - drive means (21, 121) for driving said feed screw (18, 118, 218) and said mixing tool (19, 119, 219, 319, 419, 519), said mixing tool (19, 119, 219, 319, 419, 519) comprising a rotating longitudinal body (25, 125, 225, 325, 425, 525) placed to rotate about a longitudinal axis thereof, at least one flexible scraping element (26, 126, 226, 326, 426, 526a, 526b) developing from said rotating longitudinal body (25, 125, 225, 325, 425, 525) configured to be in contact with said inner surface (22, 122, 222) of said tubular mixing chamber (15, 115, 215) at least when said rotating longitudinal body (25, 125, 225, 325, 425, 525) rotates about said longitudinal axis thereof, said at least one flexible scraping element (26, 126, 226, 326, 426, 526a, 526b) developing in the direction of said longitudinal axis between two connection points (28, 29; 128, 129; 228, 229; 328, 329) with said rotating longitudinal body (25, 125, 225, 325, 425, 525), characterized in that said at least one flexible scraping element (26, 126, 226, 326, 426, 526a, 526b) comprises a cable made of metallic material (27, 127, 227, 327, 427).