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10.8.3 Batches of neat cement or of mortar having about the same <br />proportion of cement to sand as used in the concrete shall <br />be deposited and well brushed just ahead of the new <br />concrete. <br />11 CURING CONCRETE <br />Concrete surfaces shall be adequately protected, following the guidelines of ACI <br />308, against early evaporation of water, injurious action by the sun, rain, flowing <br />water, frost, freezing, and/or mechanical injury. <br />1 1.1 METHODS OF CURING <br />One of the following optional methods shall be used unless otherwise <br />specified: <br />11.1.1 MOIST CURING <br />All exposed surfaces shall be maintained in a continuously <br />moist condition for the period specified in this specification. <br />Floor and roof slabs may be covered with a layer of sand or <br />similar material that shall be kept wet for the required <br />period. Wood forms left in place shall be kept sufficiently <br />wet at all times to prevent opening of the joints and drying <br />of the concrete. <br />11.1.2 MEMBRANE CURING <br />Pressure-spray tinted curing compounds shall be one of the <br />types specified in ASTM C 309. All compounds shall be <br />applied according to the manufacturer's directions immedi- <br />ately after finishing operations are completed. No curing <br />compound shall be permitted on surfaces where future <br />bonding with concrete or painting is specified. Such <br />surfaces shall be cured by the moist process as specified <br />herein. After final application of the curing compound, <br />surfaces shall be protected from traffic for the period of <br />time specified herein. The use of any membrane material <br />that tends to impart a slippery surface to the concrete or <br />alter its natural color shall not be permitted. The <br />compound, however, shall contain a dye of color strength <br />sufficient to render the film distinctly visible on the concrete <br />surface for a period of at least four (4j hours after <br />application. The compound shall be of such character that <br />it will harden within thirty (30) minutes. A second applica- <br />tion of curing compound shall be made one (1) hour after <br />the initial application. <br />11.1.3 POLYETHYLENE FILM <br />Polyethylene film for curing concrete should conform to <br />SPEC B -CONCRETE <br />PAGE 17 <br />