Small quantities of cement-sand screed may be hand mixed but this is hard work and unsuitable for all but the smallest sites. A void hand mixing wherever possible.
The use free-fall mixers for mixing cement-sand screed is not recommended. Small free-fall site mixers may be safely used for mixing concrete and bricklaying mortars, which are more fluid in consistency, but they are not suitable for mixing screed because they do not efficiently distribute the cement throughout the sand. Research has shown that these mixers can cause balling of cement and weakness in the finished screed. If this form of mixer is used there is a very high risk of crushing failure of the screed.
For floor screeding use forced-action mixers for site mixing screed similar to the Putzmeister M760 pictured. All forms of forced-action mixers achieve an efficient distribution of cement through the sand and produce a uniformed and potentially strong mix (see the video on this site Loading the Next Generation Floor Screed Pump).
Pan mixers may also be used and are available for hire through national tool and equipment hire companies.