Reduction of permeability is an important aim to ensure that concrete structures remain durable throughout their service life. Some commercially available permeability reducing admixtures were tested. It was found that all admixtures reduced compressive strength, absorption and air permeability. The degree of reduction depended on the admixture in question. The reduction in strength was observed because no advantage was taken of the water reducing properties of the admixtures in the mix design. An experimental parameter is proposed for evaluating the quality of concrete to take into account both strength and durability properties.