Experienced contractors rarely have trouble estimating material quantities needed for a job, but estimating labor hours can be a lot trickier. A multitude of factors affect productivity, from unit size, shape, and weight to weather conditions. What's more, all masonry tasks must be accurately measured, including the installation of flashing, anchor bolts, movement joints, and insulation. To estimate future production accurately, maintain meticulous production history records, updating your counts weekly. When your own records are incomplete, you can refer to tables and graphs in masonry estimating books, which are based on the author's field experience and research. These are no substitute for experience but can serve as guides until you establish complete production history files. Estimating production can be daunting because there are thousands of masonry unit types and accessories and myriad outside factors that can have an impact. Just make sure to count accurately every component of a masonry job at least weekly and update your production history files.