Any 1-part varnishes can be applied directly over properly prepared TotalBoat Halcyon once it has fully cured, as long as the Halcyon surface is in good condition.
TotalBoat Halcyon that is in good condition should be completely cured for at least 48 hours under normal conditions, and sanded/prepared per the recommendation of the new varnish. If the Halcyon is bubbling, flaking, or generally in poor condition, it will not provide a good foundation for the new varnish, and should be removed.
IMPORTANT! Two-part varnishes should not have compatibility issues when applied over TotalBoat Halcyon, but it is not recommended. Always test for compatibility and adhesion in a small, inconspicuous spot if a two-part varnish is strongly desired.