Mercier Pro Series Red Oak; Concrete Grey. Pro Grade. The contrasting appearance of this grade represents a mix of the species’ natural full-bodied tones. Moderate variation between boards. Knots: Sound knots and knots filled with wood putty are accepted without limitation. Openings in and around knots are accepted. Streaks: Mineral streaks are accepted without limitation. Splits and checks: Occasional surface checks and occasional end splits are accepted in this grade.