The ornamental design for a moldedsurface of a concrete product, as shown and described.
FIG. 1 is a perspective view of a molded surface of a concrete product according to our design;
FIG. 2 is another perspective view of the molded surface of a concrete product depicted in FIG. 1;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a left side view thereof;
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
The dot-dash broken lines depict the bounds of the claim and form no part of the claimed design. The dashed broken lines depict portions of the molded surface of a concrete product that form no part of the claimed design.