I’m still trying to get my head around the terminology “well graded sand” when referring to lime mixes. Is this available from most builders merchants and what exactly is it? I think I read on this website that it comprises of various sized granules from 6mm down. I’ve recently done a few patch repairs to some outside rendered walls (19th century stucco) in one case using a 25 kg bag of ‘plastering sand’ and in another case using a 25 kg bag of ‘grit sand’ which I think is sometimes referred to as concreting sand. Both of these are readily available from the 3 or 4 builder’s merchants in my area but when you ask them the granular size of the sand, they tend to give you a puzzled look. The results with the plastering sand are not too bad, where as the results with the more textured grit sand is far too harsh and lumpy. Any further advice would be much appreciated.
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Well graded sand ?
- Thread starter michael
- Start date
christianb
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- 202
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- Helford River, Cornwall
Hi Michael,
"Well-graded" is pretty much a different way of saying "sharp sand". Which is another way of saying "granite dust". "Grit sand" is a new one on me, but probably exactly the same.
6mm down is about right - anything larger and it would be like trying to plat fog.
Alas, stucco is not my natural habitat but I'd say that a much finer sand would be better to finish with.
Christian
"Well-graded" is pretty much a different way of saying "sharp sand". Which is another way of saying "granite dust". "Grit sand" is a new one on me, but probably exactly the same.
6mm down is about right - anything larger and it would be like trying to plat fog.
Alas, stucco is not my natural habitat but I'd say that a much finer sand would be better to finish with.
Christian
Thanks Christian
Yes the finer plastering sand seemed to give me the best or at least the smoothest finish results but I seem to remember it being mentioned on this site that plastering sand was an inefficient medium for binding the lime. Less granular surface for the lime to adhere to or something? So I’m keeping my fingers crossed that that section of render work doesn’t fall off the wall in due course.
Unfortunately I’m still none the wiser. How do you get a smooth finish on exterior render using a sufficiently well graded sand for binding the lime?
Yes the finer plastering sand seemed to give me the best or at least the smoothest finish results but I seem to remember it being mentioned on this site that plastering sand was an inefficient medium for binding the lime. Less granular surface for the lime to adhere to or something? So I’m keeping my fingers crossed that that section of render work doesn’t fall off the wall in due course.
Unfortunately I’m still none the wiser. How do you get a smooth finish on exterior render using a sufficiently well graded sand for binding the lime?
biffvernon
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- 4,607
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- Lincolnshire
Fine sand for the top coat of interior plaster, but otherwise use 'sharp' or 'graded' sand, i.e. stuff with a range of grain sizes from coarse to sand to silt. You get greater strength when the coarse grains just touch each other and the successively finer grains pack the successively smaller spaces between. The calcite crystals of the lime, which are nothing like as strong as the quartz crystals of the sand, just do the work of stabilising the aggregate rather than carrying much load.
To get a smooth finish go over the render with a float. A wooden float gives a slightly rough finish, a steel float gets it smoother if that's what you really want but for external render you shouldn't want it that smooth. I've also got a plastic float but I've never really got the hang of it. It tends to produce a mess.
To get a smooth finish go over the render with a float. A wooden float gives a slightly rough finish, a steel float gets it smoother if that's what you really want but for external render you shouldn't want it that smooth. I've also got a plastic float but I've never really got the hang of it. It tends to produce a mess.