Most concrete mixes for use in architectural concrete, at least all those in which aggregate is exposed, differ markedly from standard structural mixes. The type of finish desired and the materials available locally introduce considerable variation and complexity to the mix design problem. Since it is virtually impossible to produce good architectural concrete with an improper mix, architectural concrete mix design should be handled only by personnel experienced in architectural concrete. Except for the possible introduction of color, as-cast finishes very likely will not require that the mix design be different from the kind used for structural concrete. With these finishes it might, however, be necessary to design the mix for excellent workability to aid in bringing the concrete into intimate contact with forms, especially if patterns are intricate. Where aggregates are intended to be exposed the mix must be designed differently to provide the proper texture. With increasing frequency, stone sands are bing used in architectural concrete. These sands should be carefully examined for particle sharpness, which hurts mix workability, and for excessive amounts of particle passing the Number 50 sieve, which increase the water demand. A magnifying glass should be used to evaluate particle sharpness. The National Crushed Stone Association has established procedures for determining acceptability of stone sands for use in concrete.