A study was made of zircon powders bonded with phosphoric acid or aluminium orthophosphate. The influence of strength of solution of the phosphatic binders on the modulus of rupture over a temperature range was investigated. Physical properties of three grades of zircon powder bonded with phosphatic binders were studied at various temperatures. Examination of x-ray diffraction data indicated that phosphates ofzirconia are preferentially formed to phosphates of silica. However, zircon in the presence of excess phosphoric acid also forms phosphates of silica upon heating.Resistance to attack by slags from blast and open hearth furnaces was determined on phosphate-bonded zircon mortars in a cup test with industrially made ladle bricks. Zircon powders bonded with phosphates proved to have high P.C.E. values. The first satisfactory results of a plant trial with phosphate-bonded zircon mortar, used in a steel ladle, are now being assessed in larger scale industrial tests prior to accepting the mortar as a steel plant refractory.