A well-prepared background is the first step to successful plastering. New surfaces of block or brickwork may need only dampening or priming with a bonding agent, depending on their absorbency. Old plastered surfaces needing repair should be thoroughly checked. If the plaster has ‘blown’, hack it off back to sound material, then treat the surface and replaster the area.

Brush down the surface of a masonry background to remove loose particles, dust and efflorescent salts. Test the absorption of the background by splashing on water; if it stays wet, consider the surface ‘normal’. This means that it will only require light dampening with clean water prior to applying the plaster.

A dry background that absorbs the water immediately will take too much water from the plaster, making it difficult to work. It will also prevent the plaster from setting properly and may result in it cracking. Soak the masonry with clean water applied with a brush.

For very absorbent surfaces, such as aerated concrete blocks, prime the background with 1 part PVA bonding agent: 5 parts clean water. When dry, apply a bonding coat of 3 parts bonding agent : 1 part water. Apply the plaster when the bonding coat is tacky.

Prime low-absorption smooth brickwork or concrete with a solution of 1 part bonding agent : 5 parts water. Allow to dry. Apply a second coat of 3 to 5 parts bonding agent : 1 part water, and trowel on the plaster when the bonding coat is tacky. Alternatively, allow it to dry for no more than 24 hours before plastering.

Glazed tiles and painted walls are considered non-absorbent and will require a coating of neat bonding agent to enable the plaster to stick. The plaster is applied while the agent is tacky. An alternative for glazed tiles is to apply a slurry of 2 parts sharp sand : 1 part cement mixed with a solution of 1 part bonding agent : 1 part water. Apply the slurry with a stiff-bristle brush to form a stippled coating. Allow to dry for 24 hours, then apply the plaster.

You can make a useful board for mixing and working with filler from 6mm (1/4in) exterior-grade plywood. Cut out a 300mm (1ft) square with a projecting handle, or make a thumb hole as in an artist’s palette. Seal the surface with a polyurethane varnish or apply a plastic laminate for a smooth finish.

Mortar board

Cut a piece of 12mm (1/2in) or 18mm (3%in) thick exterior-grade plywood, approximately 900mm (3ft) square. Round off the corners and chamfer the edges all round. Screw three lengths of 50 x 25mm (2 x lin) softwood across the underside, spread equally apart. Make a 600mm (2ft) square ’spotboard’ in a similar way.

Using a stand

You will find it easier to handle plaster with the mix at table height.

Using a stand

Use a stand to supportthe mortar board at table height, about 700mm (2ft 4in) from the ground. This enables the plaster to be picked up on a hawk by placing the latter under the edge of the board and drawing the plaster on to it.

Construct a folding stand, using 50 x 38mm (2 x 11/2in) softwood for the legs and 75 x 25mm (3 x 1 in) softwood for the rails. Make one leg frame to fit inside the other and bolt them securely together at the centre.

A portable Workmate bench can be used to support the mortar board instead of a stand: grip the centre batten in the vice jaws.