Building Construction Handbook, Eighth Edition

Background ~ ideally level and of consistent material. If there are

irregularities, three applications may be required; render (ct. and

sand) 10†12 mm, undercoat plaster 6†8 mm and finish plaster 2 mm.

Difficult backgrounds such as steel or glazed surfaces require a

PVA bonding agent or a cement slurry brushed on to improve

plaster adhesion. A wire mesh or expanded metal surface

attachment may also be required with metal lathing plaster as the

undercoat. This may be mixed with sand in the ratio of 1 : 1.5.

Soft backgrounds of cork, fibreboard or expanded plastics should

have wire mesh or expanded metal stapled to the surface. An

undercoat of lightweight bonding plaster with compatible finish is

suitable.

Dense regular surfaces of low-medium suction such as plasterboard

require only one finishing coat of specially formulated finishing

plaster.

Corners ~ reinforced with glass-fibre scrim tape or fine wire mesh

to prevent shrinkage cracking at the junction of plasterboard

ceiling and wall. Alternatively a preformed gypsum plaster

moulding can be nailed or attached with plaster adhesive (see page

725). Expanded metal angle beads are specifically produced for

external corner reinforcement. These are attached with plaster

dabs or galvanised nails before finishing just below the nosing.

galvanised steel

expanded metal

Plastered walls Plasterboard walls

nosing

External Corner Beads

Plaster Application