The activators have formula (in which R1 and R2 are alkyl groups with 1-4C atoms, or aryl groups which may be halogen-substituted, and R3 and R4 are alkyl groups with 1-5 (pref. 1-3) C atoms). Preferred compositions have 60-95% (pref. 80-90%) insoluble scouring agent, and a combination of per compound and activator such that the number of acyl groups per mol. of inorganic bound H2O2 is between 10 and 0.1 (pref. between 4 and 0.5). The scouring powders do not have the smell problem of chlorine-containing types and are more active in cold conditions than those based on per compounds without the activators.