From Longman Dictionary of Contemporary Englishundercoatun‧der‧coat /ˈʌndəkəʊt $ -dərkoʊt/ noun [countable] DHHa layer of paint that you put onto a surface before you put the final layer on → topcoat
Examples from the Corpus
undercoat• Yellow ochre is a colour I often use for both undercoats and overpainting, having a good semi-transparent quality.• But it's rather interesting - it's brown undercoat.• After priming, the correct colour undercoat is applied, followed by two coats of gloss.• Amount of undercoat is influenced by climatic conditions.• Hammerite is a unique paint: it dries to a very hard finish, and needs no primer or undercoat.• It can be used on wood and metal, and needs no primer or undercoat.• In some places the reddish undercoat of the frame shows through the gold moulding, echoing the reds in the picture.• The undercoat is grey or black. 