An enclosure device for a concrete column formwork uses an envelope comprising a tubular wall portion and a top portion supported on the formwork such that the wall portion extends about a perimeter of the column formwork and extends vertically along a height of the column formwork and such that the top portion encloses a top end of the wall portion. The envelope also has brace openings to receive formwork braces extending therethrough and slots in the envelope communicating between the brace openings and a bottom edge of the wall portion so that the envelope can be lowered downwardly over the column formwork as the braces are inserted upwardly through the slots into the brace openings.