A method and apparatus for capping and encapsulating a shaped wooden workpiece or substrate to protect against environmental elements and prevent splintering of the wooden substrate in the installed condition is disclosed. An inventive end cap having a melt ring integrally formed therewith is installed on a portion of the substrate, such as a terminus of the substrate. According to the invention, the wooden substrate is sheathed during a polymeric extrusion process with a substantially continuous, unbroken polyethylene or other polymeric layer extending from and continuous with the inventive end cap. During the extrusion process, the melt ring integrally formed along the annular walls of the end cap melt the encapsulant and form a substantially sealed configuration with the polymeric layer applied to the substrate. The melt ring is engineered to sealingly incorporate with the polymeric extrusion as the molten encapsulant is applied to the wooden substrate, to provide a substantially uniform sealed joint between the end cap and the polymeric layer while maintaining a substantially uniform cross-section along the length of the wooden substrate following completion of the encapsulation process.