Coated inorganic expanding agent particles comprise a core of an inorganic expanding agent and a sol/gel-formed coating comprising a mixed oxide of two or more metals and/or metalloids, in particular a mixed oxide of silicon and at least one metal and/or metalloid selected from aluminum, boron, titanium, zirconium and zinc. The coated inorganic expanding agent particles are added to cementitious systems to avoid shrinkage during hardening. The coating is effective to delay the expanding effect.