Exhibit 23.1 Consent of Independent Auditors We consent to the incorporation by reference in the Registration Statements (Form S-8 Nos. 33-61322, 333-60381, 333-30878, 333-60316, and 333-113752) and (Form S-3 Nos. 333-38246, 333-38218 and 333-109682) of Spartech Corporation of our report dated December 17, 2004, with respect to the consolidated financial statements and schedule incorporated by reference or included in the Annual Report (Form 10-K) for the year ended October 30, 2004. /s/ Ernst & Young LLP St. Louis, Missouri January 13, 2005