Blueboard

Part of speech: noun

Definitions

1. A type of gypsum plasterboard with a blue-tinted paper face, used as a base coat for plaster on walls and ceilings
2. Building board whose blue-coloured paper surface is designed to hold a plaster finish applied over it in construction work
3. A panel of gypsum board faced with blue paper, fixed to walls and ceilings so that plaster can be applied to its surface

Etymology: Blueboard is a compound of "blue" and "board," and its history is almost entirely a matter of the building trade's own vocabulary. "Plasterboard" was the usual name for the gypsum-core panels that replaced wet plaster on walls and ceilings, and the blue variant is a plasterboard with a distinctive blue-grey paper face. That face is the key to the name: it is designed to take a skim coat of plaster, which bonds to the paper, so the wall can be finished in one smooth layer rather than the traditional three-coat method. The blue colour is a practical marker rather than a decorative choice. Manufacturers dye the paper so that installers can tell the boards apart from standard grey or white plasterboard at a glance, which matters because the different types need different finishing. The word itself appears in British building usage, and the specific dates of its first recorded use are not something I can confirm.