4.1 Molds, General—Molds for specimens or fastenings
thereto in contact with the concrete shall be made of steel, cast
iron, or other nonabsorbent material, nonreactive with concrete
containing portland or other hydraulic cements. Molds shall
conform to the dimensions and tolerances specified in the
method for which the specimens are required. Molds shall hold
their dimensions and shape under all conditions of use.
Watertightness of molds during use shall be judged by their
ability to hold water poured into them. Test procedures for
watertightness are given in the section on Test Methods for
Elongation, Absorption, and Watertightness of Specification
C 470/C 470M. A suitable sealant, such as heavy grease,
modeling clay, or microcrystalline wax, shall be used where
necessary to prevent leakage through the joints. Positive means
shall be provided to hold base plates firmly to the molds.
Reusable molds shall be lightly coated with mineral oil or a
suitable nonreactive release material before use