NOVELTY - A manufacture of curable composition involves using organic polymer (A) having silicon-containing group which is crosslinked by forming siloxane bond, and heavy calcium carbonate (B) (30-500 weight parts with respect to 100 weight parts of organic polymer (A)). The organic polymer (A) is reactive silicon group-containing organic polymer (a1) (30-100 weight% with respect to total amount of organic polymer (A)). The heavy calcium carbonate is surface-treated heavy calcium carbonate (less than 60 weight%).    USE - Manufacture of curable composition used for joint structure such as bed-joint structure (both claimed). Uses include but are not limited to electrical insulation material such as electrical and electronic components material, solar cell back surface sealing material, electric wire insulation material and cable material, elastic adhesive agent, spray-type sealing material, crack repair material, casting material and medical device sealing material.    ADVANTAGE - The method provides curable composition having favorable mechanical strength, hardenability, excellent wettability with respect to joint structure, adhesiveness with respect to base material and joint structure and low viscosity.    DETAILED DESCRIPTION - A manufacture of curable composition involves using organic polymer (A) having silicon-containing group which is crosslinked by forming siloxane bond and heavy calcium carbonate (B) (30-500 weight parts with respect to 100 weight parts of organic polymer (A)). The organic polymer (A) is reactive silicon group-containing organic polymer (a1) (30-100 weight% with respect to total amount of organic polymer (A)). The heavy calcium carbonate is surface-treated heavy calcium carbonate (less than 60 weight%). The reactive silicon group of is of formula: -(CR12)2-SiX3.    X=hydroxy or hydrolysable group;and    R1=H or (un)substituted 1-20C hydrocarbyl.    An INDEPENDENT CLAIM is included for manufacture of fluid adjusted curable composition, which involves adjusting the fluidity of curable composition.