Difficulties were being experienced at the plant of Haley Industries Limited, with the use of reclaimed CO?-process sand. Mixtures made with this sand were difficult to mould because of poor flowability, and there was an increased occurrence of defective castings. The usual tests for mouldability and flowability did not differentiate between mixtures with good and poor properties. Usability of the mixtures was found to be related to changes with time of green and gassed compressive strength, of permeability, and of density of the test specimens. A reaction between coatings of silica gel on the grains of reclaimed sand and the new sodium silicate of the mixtures was found to be the main cause of the problem. Probably also contributing were sodium salts and unreacted sodium silicate, which dried out the mixtures. It was also found that the effect of these ingredients could be eliminated adding 0.5% of 5N NaOH to the mixture.. The order of adding the lye and sodium silicate was not important. When these results were applied at the plant of Haley Industries Limited, mixtures containing 50% reclaimed sand and 50% new sand were found to have good properties. This is in contrast to the maximum of 25% which could previously be tolerated. The use of 50% reclaimed sand is considered to be a satisfactory objective, and the problem is now. Under control.