Initial Base Coat of Paint
Puzzle 20 of Building a House Hard Pack
Question is: Initial Base Coat of Paint
and the answer is: PRIMER
Word Meaning:
PRIMER — (historical, Catholicism ecclesiastical) A prayer or devotional book intended for laity, initially an abridgment of the breviary and manual including the hours of the Virgin Mary, 15 gradual and 7 penitential psalms, the litany, the placebo and dirige forming the office of the dead, and the commendations.
Definitions from Wiktionary.