Abstract: A deflocculating mechanism for use in a paper making machine includes a support member such as a forming board or a foil blade for location beneath a forming fabric belt. The support member has an upper surface defining at least one groove that runs in a cross-machine direction, the groove being provided with retention device for holding an insert in a sliding engagement in the groove to induce micro-turbulence in pulp stock being carried by the forming fabric belt. A pressure pulse commences in the pulp stock from a single source at one side of the forming fabric as it passes over the leading edge of the insert and then travels across the fabric along the line of the insert as a single wave. This produces a more controlled agitation and deflocculation of the pulp stock.