Sentence:  He improvised as he went along , completing a life-size clay figure , then bought yards of an inexpensive material from a draper , wet the lightweight cloth in a basin and <WSD>covered</WSD> it over with clay that Argiento brought from the bank of the Tiber , to the consistency of thick mud . 
Meaning of the word marked with <WSD> tags:  provide with a covering or cause to be covered