From DIYinfo.org
For any plastering job, even a small one, it is essential to have good quality equipment. A list of the tools needed to repair small holes in plastered walls is covered in Tools For Plastering What You Will Need.
For larger jobs you also need:
Setting-out Boards:
A number of battens of wood 12mm square and the length of the wall to be plastered are necessary for setting out the wall prior to the floating coat. These are placed at about one metre intervals along the wall and at each end of it. They should be cut exactly 12mm wide since this corresponds to the depth of the first coat of plaster.
A length of board about 100mm wide and the height of the wall is also needed when plastering corners.
Straightedge:
For levelling out areas of plaster, a straightedge about 1.5 metres in length is used, or a straight batten of wood about 50mm wide will be just as effective.
Plumb line and spirit level:
To align the setting-out boards accurately prior to plastering it is essential to have an accurate spirit level and efficient plumb line.
Mixing Bucket:
To avoid unnecessary mess when preparing the plaster it is useful to have a large plastic bucket for mixing. This also helps to gauge more accurately the exact amount of water and plaster needed to reach the required consistency. For cleaning tools and wetting down walls it is also useful to have a second bucket full of clean water.
Wetting Brush:
To help the plaster to adhere, the surfaces need to be wetted down and a wide paint or distemper brush makes this task easier.
Shaping Trowels:
Once the finishing cost is applied, it is often difficult to achieve a neat finish around external and internal corners (the joint between a wall and ceiling is an internal corner). To do this accurately, internal and external angle trowels are available.
Scaffold Square:
One of the most difficult areas to finish accurately when plastering is around door and window reveals. To help with this a scaffold square, consisting of three pieces of wood formed into a right angle, is necessary. This is held hard against the door or window frame so that the plastering along the reveal can be checked.