Plaster mixing can be done by hand with a suitable bucket and a piece of wood to do the mixing, however it is much easier to mix plaster using either a plaster mixing machine or a suitable drill with a mixing paddle. This kind of work is tough on drills and can easily burn out small power drills in no time at all.
When mixing plaster or dry wall adhesive always put the water in the bucket before adding the plaster! If you try adding the plaster then the water it goes lumpy and has to be thrown away.
Add clean cold water to the mixing bucket and ensure that the bucket has been cleaned sufficiently from the last time it was used.
Now add some plaster, you can add large amounts to begin with but it's better to use a gauging trowel for adding plaster later. Try not to make a lot of dust when doing this as it could irritate.
Here we are using a mixer drill and paddle to mix the plaster, this makes it so much easier. If you have no mixer drill a smooth piece of wood can be used to mix the plaster.
Here the plaster has been mixed to the correct consistency and it is completely lump free! This can now be used.