The paper describes an experimental investigation into cracking in edge-restrained reinforced concrete walls cast onto concrete bases. The aim of the investigation was to study the mechanics of cracking in relatively thin edge-restrained walls (< ∼ 500 mm) in which through thickness temperature variations due to heat of hydration can be neglected. Twelve walls, each 5.2 m in length, but with varying thickness, height, concrete mix design, reinforcement, and formwork insulation were monitored over a period of at least 3 months. Detailed measurements were made of the temperature rise during heat of hydration, strain and crack width. The paper describes the experimental results in detail, including the development of cracking with time. The measured restrained strains, time of cracking and crack widths are compared with those calculated with EC2–04, EC2–23 and Ciria Report C766 which all adopt the same unrealistic model for calculation of crack width. EC2–04 gives the greatest crack widths and C766 the least due to the lower adopted restraint factor. Significantly, C766 was found to greatly underestimate the maximum measured crack widths with EC2–04 and EC2–23 providing more realistic estimates. Based on the observed cracking behaviour, the paper proposes a simplified mechanical model for the calculation of crack width in relatively thin edge-restrained walls.