Formwork carpenters assemble manufactured wood forms,. The work is physically demanding and messy, consisting of carrying the heavy forms, spraying them with oil that keeps the concrete from sticking, securing them with iron rods and inserting steel reinforcement that will give the concrete tensile strength. Once the concrete sets, formworkers strip the forms, clean them and prep them for the next project. In the case of high-rises and tall structures, formworkers build new forms on top of previously poured concrete. Called slip-forming, the work follows a repetitive process of forming.