Profile: Keyline Builders Merchants is a supplier of building materials and products. Our product line includes decorative aggregates, bagged sands & gravels, building aggregates, plasters, macadam & dry mixed concretes, mortars, bricks, blocks, lintels, damp proof, barrier membranes, ducting pipe systems, flow regulators and fencing systems. Our damp proof membrane provides an effective barrier against the ingress of liquid water and water vapor through base concrete.