Calcium silicate powders are provided. The calcium silicate powders comprise porous calcium silicate particles and an additive, the additive being at least partially penetrated into the pores of the particles. The additive is present in an amount of between 1.5 and 50%w, wherein %w is the weight ratio, expressed as percentage, of the dry weight of the additive over the dry weight of the combination of the calcium silicate particles and additive.