Abstract: An apparatus for applying mastic to a selected surface includes a container for mastic, a pump assembly, and a drywall tool or wand. The pump assembly is positioned in the container so that it draws mastic from the container and delivers it to the drywall tool. The mastic delivered to the drywall tool is applied to the selected surface through a nozzle in the drywall tool. The pump assembly includes a pump, a pneumatic cylinder, and a linking subassembly connecting the pump and the pneumatic cylinder. The pump assembly is operated by an air compressor. The air compressor causes a rod in the pneumatic cylinder to reciprocate. The linking subassembly translates this reciprocation to a piston in the pump assembly. The piston reciprocates within a bore of the pump assembly and draws the mastic from the container. The apparatus is mounted on a hand truck so that it may be moved to different locations.