Cold weather concreting poses problems that are generally recognized in the field because there's no escaping them. It's easy to see that a pour that has frozen is a loss. The results of poor practices in hot-weather concreting are far more insidious and often more serious. A frozen floor slab must usually be torn up and replaced with a good one; a floor slab damaged by high temperatures and low humidity will generally be left to bear mute but eloquent testimony to poor workmanship. The most that can be expected of a ready mix supplier is that he will deliver the specified mix at the correct time and temperature. After that it's up to the men on the job to handle the concrete in a manner that will assure good results. High temperatures accelerate the rate of hardening of concrete and also promote rapid evaporation of the mix water, especially in slabs where surface area is great compared with volume. This means that forms have been set in place, all tools and materials are ready, and enough workmen are on hand to pour and finish the concrete quickly. An important part of the preparatory measures is dampening the subgrade. This is best accomplished by thoroughly soaking it the night before pouring, and then sprinkling it shortly before the concrete is poured. During particularly hot weather, concreting is often done in the cool of the night. It is best not to get too ambitious in regard to the amount of concrete to be placed at any given time. If work is being done in exposed locations, a windbreak and shading of the concrete are highly desirable while waiting for the concrete to harden sufficiently for finishing. Curing must be started as soon as possible after finishing. If it is delayed faster then the bulk of the concrete and result in crazing. Be sure to keep concrete damp during the entire curing period.