A stage tool includes an isolation mechanism for isolating the lower bore of a completion string. The isolation mechanism is initially in a deactivated configuration until sufficient hydraulic pressure is applied, at which time, the isolating mechanism is activated to isolate the lower bore from cement ingress. Concurrently or subsequently, a stage tool may be opened to facilitate cementing of an annulus between the completion string and the wellbore. After cementing, the isolation mechanism, or portions thereof, may be drilled out to re-establish flow through the stage tool.