Cement mixing
There are several ways to mix mortars.
In almost all cases the dry components are mixed first, then water is added and mixed in. There are also times when mixes are used dry.
Cement mixer
Very popular, but too expensive and bulky for small jobs. Storage is often impractical. Its often cost effective to buy one for a job then resell afterwards.
Always rinse out before the cement sets if you want the machine to last well.
Can be used to break soft bricks down into powder/pieces which can be incoporated into some mortars. See Pozzolan for information.
Can also be used to break glass into cullet. Add the glass and add a hard brick. Ditto scrap tiles.
Paddle Mixer
See Paddle mixer
Better suited to paints and lime mortar than cement.
When used with haired or fibre reinforced mortar mixes these tend to form 'dead mice' on the paddles (clumps of hair).
Hand held paddle mixers for use in drills put a lot of load on a drill. A high power low speed mixing drill should be used. Using paddles in a cordless drill is not realistic.
A small makeshift paint mixer can be made by bending some 2mm iron wire if you keep the shaft short and the stirrer narrow. These are only usable for paint mixing, not mortar.
Board & Shovel
Mix sand & cement dry on board. Make a ring of the mixture. Add a little water in the middle and fold the dry mix in. Repeat until mixed.
Its not practical to use a plastic sheet instead of the board, the rigidity is needed.
Sandpit
This is a flat board with raised edges. Mix dry materials, then add water and mix in. Unlike a board its not necessary to maintain a ring of mixture to prevent water escape, making it quicker.
Bucket & Shovel
Don't fill too full, or you won't be able to mix. Over half full is hard to mix. Some tendency not to mix material at the bottom well, so the bottom of the mix needs extra attention.
Fast Bucket Method
For small amounts its faster to toss the bucket than mix with a small shovel. The bucket needs to be a quarter full or less. Shake the bucket rapidly up & down in an oval () shaped motion, and the contents go round and mix very quickly. At 2 tosses a second, a batch can be done in 20 seconds once the water is added. Energetic work, but very quick.
Tarpaulin
Place tarp on the ground, in a shallow hollow depression if available. Mix dry sand & cement, add water, then 2 people lift opposite corners alternately to mix the mortar. Quick.
Mortar Board
Very small amounts can be mixed on a hand held mortar board with a trowel. The same ring technique is used as with a full size board.
Mega mixer
For really large batches it is possible to make a giant mixer driven by a car engine. These can be scaled up versions of a cement mixer for cement mortars, or a giant version of a food processor for Papercrete and similar formulae.
Suited to large cement mixing jobs, Papercrete and similar mixtures. Making one is not a trivial exercise. Purchasing an industrial mixer is prohibitive.
http://www.livinginpaper.com/mixers.htm