Abstract: Trim moldings such as crown molding, chair rail molding, base molding and door casing for a building. The trim moldings are made of substantially acrylic or polyester rigid thermoset polymer components. The trim moldings may be manufactured to realistically visually simulate moldings made of natural stone. A method of manufacture of the moldings may utilizes bulk slabs or blocks of rigid thermoset polymer based materials which are then properly shaped for use as a building trim molding with mechanical material removal methods such as sawing, cutting, sanding, and polishing to achieve the desired size, shape and appearance of molding. The thermoset polymer based moldings are structured with grooves in the backside, with the grooves sized and positioned to snap onto spring biased members of mounting fixtures attached to the building for a removable attachment of the moldings.