A process to manufacture and coat a sodium carbonate perhydrate containing 10.5% to 14% active oxygen which is stable in a non-phosphate detergent composition and which has a bulk density of from 900 to 1,050 kg/m.sup.3. Anhydrous sodium carbonate with a pore volume of at least 0.29 ml/g is contacted with 50% to 75% by weight hydrogen peroxide in the presence of 1-hydroxyethylidene-1,1-diphosphonic acid and water is evaporated at a rate to maintain a dry reaction mixture. The product is coated by sparging sodium borosilicate at a rate to avoid moistening the particles.