Premature setting of concrete can have some disastrous effects on profits and job timetables. Flash set might take place with a hot mix on a warm, windy day. Floor slabs can set up before finishing is completed, thereby necessitating expensive, time-consuming resurfacing or grinding. Deep beams might harden in layers causing undesirable cold joints. Casting deck slabs for continuous or composite bridges can result in cracking if the concrete hardens while the girders are deflecting form the weight of green concrete being placed elsewhere on the deck. Contractors must delay the set around decorative aggregates to obtain maximum reveal and the best possible color. The list is long- there are many cases when a speedy set can mean a delayed or inferior job. The common way to slow the hardening of concrete is to employ an admixture termed a retarder. Unfortunately, there exists some confusion regarding the correct application of retarders and water reducing agents. Retarders are intended for use only in hot weather; water reducing agents should be added during normal temperatures. Water reducing agents reduce the water-cement ratio, resulting in higher strengths. Retarders are primarily intended to counteract the harmful results of heat on the concrete mix; they lower the water/cement ratio only as a side effect. Just remember, don't use retarders in cold weather. Naturally, all other things being equal, the more retarder that is added to the mix, the greater will be the delay of the set. Contractors can simplify matters by attempting to keep job conditions as uniform as possible. Be ready to accept ready mix as soon as it is delivered to avoid build-up of heat. Shade the concrete from the sun's direct rays. On hot, dry, windy days erect windbreaks around slabwork. By keeping job conditions comparatively constant, setting time can usually be controlled.