Refers to the traditional lime-based wall coating used in Japanese architecture; can also refer to similar materials in general construction.
The walls of the old storehouse are coated with shikkui plaster.
The craftsman mixes the mortar and applies it to the wall.
Standard kanji spelling, though the characters are ateji (phonetic).
Kana spelling is common in everyday writing, especially when the ateji kanji are not needed.
The reading しっくい is of uncertain origin; the kanji 漆喰 are ateji (phonetic) and do not reflect the meaning.