As experienced concrete floor contractors know, no single mix design is suitable for all jobs. Varying jobsite conditions and performance requirements often call for adjustments in mix design to achieve satisfactory results. Ross Martin, vice president of engineering technical services for Baker Concrete Construction has developed a table which gives alternative mix designs for various job conditions. Martin says the mix designs exhibit reasonably predictable and uniform setting characteristics. Because less-than-ideal placing conditions are normal, it's important for concrete mixes to be "user friendly."