The most common horizontal members are beams and slabs. There are certain necessary techniques for placing, distribution, and compacting plastic concrete in these, especially when they are heavily reinforced in the negative moment region over continuous supports. Good practice for placing and distribution will necessitate the following measures: the fresh concrete must first be deposited without segregating the coarse and fine aggregates so as to eliminate patches of stoniness or excess fat; the deposited fresh concrete must then be distributed to an even depth using a surcharge to allow for the compaction of the plastic mass; and workmen must be prevented from walking over the fresh concrete after it has been spread and before compaction, lest they produce spotty precompaction that will cause an uneven surface after vibration. At the start of internal vibration of concrete in floor and roof slabs the vibrator should be inserted at an angle with the direction of the top steel, avoiding contact of the vibrator with the bottom form so as to prevent damaging it and should be thrust forward for a distance of a few feet while resting on the upper surface of the bottom bars. The same procedure is used for girders and beams but particular care must be taken to ensure that in these flexural members the vibrator can be supported by the stirrups of ties, or otherwise prevented from contacting and possibly damaging the side and bottom formwork. In densely reinforced members the consolidation of fresh concrete in the forms requires more time and energy to ensure complete embedment of reinforcement and full compaction. This is because the steel absorbs a great deal of the energy from the vibrators. In horizontal members with top reinforcement the delivered concrete sometimes arches over the bars. To make it move down between them the vibrator must be inserted in a horizontal position just above the bars. The usual concept is to use more workable concrete under such circumstances. This requires more water and cement be used for a given water-cement ratio, but it causes more shrinkage and creep. Instead of using concrete of high slump, it is most advisable to group the reinforcement to allow the passing of heavier vibrators of appropriately larger size.