FEATURE particle shape of natural sands tends to be rounded due to weathering whereas that of crusher sands tends to be angular or flaky . Some river sands , however , contain newly weathered particles with a rough surface texture and angular particle shape . These particles are normally in the coarser fraction of the sand and should be screened out .
The water used in the plaster mix should be fit for drinking . Provided sufficient attention is paid to the selection of materials , mix proportions , preparation of substrate surfaces and the application of the plaster , the results should be serviceable and aesthetically acceptable .
The water used in the plaster mix should be fit for drinking .
Increasing these fractions results in increased water requirement ( with consequent lower strength and higher shrinkage ), but improved workability and water retention . The optimum fines content is therefore a compromise between these properties .
For plasters , sand lacking in fines may be used in conjunction with hydrated builder ’ s lime , mortar plasticiser , or masonry cement , or it may be blended with fine filler sand .
Ideally , for good workability , the particle shape should be nicely rounded with a smooth particle surface texture . The
The School of Concrete Technology ’ s SCT12 course , ‘ Mortars , Plasters , Screeds and Masonry ’ is presented online . For more information on this tuition or plastering in general , refer to the CCSA publications , ‘ Successful Plastering ’, and ‘ Common Defects in Plasters ’, both available from the website www . cemcon-sa . org . za or phone CCSA on + 27 ( 0 ) 11315 0300 or email info @ cemcon-sa . org . za .
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