Joined: July 2004
||Posted: 09 July 2019,10:48
SBR will indeed 'beef up' the mortar, but it alsop makes it incredibly tricky to use, as any minor spill, smear or spolsh WILL stain the paving, and stain it permanently, unless it is meticulously cleaned up immediately.
As a contractopr, we oonly ever used SBR in the jointing mortar of commercial projects where we could expect vehicle overrun and/or thousands of pedestrains per day. This is because, without such traffic loadings, there's no need for SBR, and also because of the need for meticulous cleanliness.
For a residential patio, a well-mixed 4:1 sand/cement mortar with a simple plasticiser is more than adequate for the jointing. No need whatsoever to over-engineer the job.
Building/soft sand will give a smoother, finer mortar, while grit/sharp sand will give a coarser finish. It's not a matter of one being structurally better than the other: it comes down to which you prefer to look at.
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