Bonding coat
The bonding coat, bond coat or base coat in construction terms usually refers to the first coat of gypsum plaster which is laid on the existing surface such as stone, brick or existing plaster. The term base coat is usually used to mean the same but for lime based plaster products or clay based plaster products. Base or bond coat can also be used to describe the first layer of external render applied directly to the existing external structure of a building such as stone or brick, though this is most often referred to as a parge coat.
The bond or base coat is usually a coarse plaster or render which can be applied in thicknesses between 10-20mm, it has greater adherence qualities and is used to even out the existing surfaces of the wall, internally in the case of plaster and externally in the case of render. Once hardened one or two more layers can be applied, finished by the final coat, finish layer, sometimes called skim coat which is normally a thinner layer applied at 2-5mm thickness.
See also: plaster, lime plaster and clay plaster
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