A mixing applicator for mixing a fluid substance with a solid substance to obtain a resulting substance having a desired consistency, the applicator comprising: a hollow elongated barrel having distal and proximal openings, the elongated barrel having a first cross sectional shape along a first proximal portion of the elongated barrel defining a first chamber, and a different second cross sectional shape along a second distal portion of the elongated barrel defining a second chamber, the second cross sectional shape extending from the distal end of the first portion to the distal opening of the hollow elongated barrel; a first and a second valve both slidably displaceable within the hollow elongated barrel and sequentially arranged along a longitudinal axis of the barrel, the first and second valves having a third cross-sectional shape being complementary to said first cross sectional shape, thereby providing fluid-tight engagement within said first cross-sectional shape, said third cross-sectional shape being mismatched with said second cross-sectional shape to form a mismatch zone along a length of said second chamber, said mismatch zone allowing fluid flow around the valves, said second chamber being longer than a combined length of said first and second valves as measured along a longitudinal axis, thereby to allow said first and second valves to effect mixing of said fluid substance with said solid substance and subsequently to remove excess fluid to obtain said resulting substance having said desired consistency, wherein the third cross-sectional shape of both the first and second valves comprise a circular cross-sectional shape, characterized in that the second cross-sectional shape of the second chamber comprises a hexagonal cross-sectional shape, that a fit between the third-cross sectional shape and the second cross-sectional shape in the mismatch zone provides a seal for the valves to seal against the solid and the resulting substance, and that said fluid substance is a biocompatible fluid housed in the first chamber between the first and the second valve and said solid substance is a pre-cementitious material housed in the second chamber between the second valve and the distal end, the pre-cementitious material forming a cementitious material upon mixing with the biocompatible fluid. a hollow elongated barrel having distal and proximal openings, the elongated barrel having a first cross sectional shape along a first proximal portion of the elongated barrel defining a first chamber, and a different second cross sectional shape along a second distal portion of the elongated barrel defining a second chamber, the second cross sectional shape extending from the distal end of the first portion to the distal opening of the hollow elongated barrel; a first and a second valve both slidably displaceable within the hollow elongated barrel and sequentially arranged along a longitudinal axis of the barrel, the first and second valves having a third cross-sectional shape being complementary to said first cross sectional shape, thereby providing fluid-tight engagement within said first cross-sectional shape, said third cross-sectional shape being mismatched with said second cross-sectional shape to form a mismatch zone along a length of said second chamber, said mismatch zone allowing fluid flow around the valves, said second chamber being longer than a combined length of said first and second valves as measured along a longitudinal axis, thereby to allow said first and second valves to effect mixing of said fluid substance with said solid substance and subsequently to remove excess fluid to obtain said resulting substance having said desired consistency, wherein the third cross-sectional shape of both the first and second valves comprise a circular cross-sectional shape, characterized in that the second cross-sectional shape of the second chamber comprises a hexagonal cross-sectional shape, that a fit between the third-cross sectional shape and the second cross-sectional shape in the mismatch zone provides a seal for the valves to seal against the solid and the resulting substance, and that said fluid substance is a biocompatible fluid housed in the first chamber between the first and the second valve and said solid substance is a pre-cementitious material housed in the second chamber between the second valve and the distal end, the pre-cementitious material forming a cementitious material upon mixing with the biocompatible fluid.