Dictionary.com defines 'parget' as "any of various plasters or roughcasts for covering walls or other surfaces, especially a mortar of lime, hair, and cow dung for lining chimney flues. " The verb 'to parget' means "to cover or decorate with parget or pargeting"; by implication, a pargeter is someone who pargets.
I have seen it written that a pargeter is particularly one who does "decorative lime plasterwork" (my italics). The dictionary.com definition, with its reference to cow dung and chimney flues, suggests the opposite: that pargeting is actually a very utilitarian form of plastering.
© Haydn Thompson 2017