A composite lay up tool comprising a metal faceplate (12) on a support member (13), wherein the faceplate has been formed by cold-gas dynamic spraying of particles of the metal onto a substrate and wherein the support member is compatible with the faceplate and comprises a casting of a ceramic composition. A process for forming the tool is disclosed. In one aspect, a castable ceramic composition comprises a binder and an aggregate component mixable with water to form a slurry ready for casting, wherein the aggregate component is one of, or a mixture of, fused silica and a particulate metal alloy, and the binder and aggregate component are present in the proportions 10-50 wt % and 90-50 wt % based on the dry weight of the composition. Also disclosed is a process for producing a faceplate for a lay up tool, which process comprises cold-gas dynamic spraying of particles of a nickel-iron alloy onto a substrate to form a faceplate of the nickel-iron alloy on the substrate, the faceplate being of a thickness in the range 2 to 10 mm. Further disclosed is a process for depositing a metal on a faceplate of a lay up tool in which the faceplate is formed of a nickel-iron alloy, which process comprises preparing an area of a surface of the faceplate to effect cleaning and conditioning of the area to accept and adhere to cold-gas dynamic sprayed particles, and cold-gas dynamic spraying particles of the metal onto the cleaned and conditioned area, wherein the metal is a nickel-iron alloy selected to be compatible with the faceplate.