why sharp sand render after DPC

having had Chemical DPCs put in in the past, I'm always curious as to the reason for the specification of render that the DPC company insist on..Salt/Water retardent is fairly obvious, but why Sharp sand as opposed to any other (washed) sand ? Is Sand generally unwashed when you buy it from the likes of Jewsons...can you taste the salt if you're so inclined ? Is Sharp sand recommended as it's more bulky and therefore cheaper to render to the thickness spec'd (10mm + 10mm in my case...+3mm finish).
Cheers, Ant.
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ANt wrote:

Normally an waterproofing admixture is used.

It makes a stronger and more coherent render. However, externally, render is best done with a sand composed of almost uniform particles with no fines", like granulated sugar. I've always ordered this as "rendering sand", I guess there's a special name (LB?).

Depends... "washed" or "washing".... Ordinary builders' sand is not washed, you can tell as it stains....

Are you thinking of beach sand? Beach sand isn't used, at least not that I know of, in mainstream construction.
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