I've always been unsure about when to use the different types of sand. Obviously it's sharp sand for screed and builders sand for bricklaying mortar but can someone tell me why? I'm about to bed a shower tray with mortar (per manufacturers instructions) but can't decide whether to use sharp sand or builders sand - ?
Dave
I think it's to do with workability: soft sand has many grades of rounded particles, right down to clay. This makes it handle well and you can adjust bricks easily, the mortar made with soft sand supports the bricks but allows plenty of movement if you need it.
Sharp sand has angular grains, less gradation, and I believe makes a stronger mortar, but it won't handle well or have the range of adjustment that soft-sand mortar does. My experience with soft-sand is very limited, but I have a fair bit with sharp sand, and found that if you didn't get the thickness off mortar right first time when bricklaying or laying paving stones on a solid bed of mortar, then if you tap the brick/paving down only a limited amount of adjustment occurs before it locks up solid, then it's take the brick/slab up and start again. It also allegedly doesn't handle well on a trowel. I built a wall using sharp sand as I wanted white mortar, and the local sharp sand is silver, but it wasn't easy.
Supposedly mortar can be made to handle better by using a plasticiser, which is either lime, or a proprietary plasticiser, like PVA or Febmix ( or squeezy if you're a cheapo! ).
I'm not an expert, but bedding something like a shower tray makes me think a mortar that allows a goodly amount of adjustment is best, so I'd try the soft sand. There is a special cement for bricklaying, masonry cement, that does not need additional plasticiser, but if you're using ordinary Portland cement, I think some lime or plasticiser added to the mix will be beneficial ( e.g. 1:1:6 lime/cement/sand ).
PS: I defer to anyone else who's had years of experience in the trade and knows better!
Andy.
Sharp sand is used for renders and screeds,also used dry for bedding block paving and slabs.
Is there any reason why graded crushed glass couldn't be used in admixture with sharp sand?
AJH
I thought that essentially that is what sand actually is.
Why on earth we dont just throw bottles into a smasher and then into the sea and let that do the job of reducing them to coloured pebbles and sand I don't know...
Because it's more economical to reuse it as glass?
Sand and glass are not really the same thing, though sand is used in the manufacture of glass. Sand is mostly the crystalline form of silicon dioxide known as quartz. The yellow/brown colouring comes mostly from iron oxides. Glass is made by melting sand with sodium and other metallic compounds and then supercooling it to form a non-crystalline solid. Glass is not nearly as hard as quartz but the main reason for not using it as an aggregate is that it is much more valuable than sand.
Unless you are being paid for how many zillion bricks per hour you can lay, sharp sand is perfectly good enough for building and the mortar will indeed be stronger than with soft sand. More importantly, if you want to be on the side of the angels, don't use Ordinary Portland Cement at all. Build with lime mortar, a 3:1 sand : lime mix. The best lime to use comes wet in a plastic tub and is called lime putty but a cheaper alternative is the bagged hydrated lime available from all buildres' merchants. Buy it from a merchant with a rapid turnover and empty the bag into a plastic dustbin of water as soon as possible and then use it wet because the lime cabonates on contact with the air.
Thanks to one and all.
Dave
Have you come accross "washed sand" yet ?
Rick
Yeah, I washed some building sand the other day. What stayed suspended in the water was a surprisingly large amount of something called limonite, which is a kind of clay tinted with yellow oxide.
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And keep your work covered for how long to protect it from the rain?
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I'm tempted to say that washed sand is what you get when you add a dash of washing up liguid to the mortar to make it easier to work. Really it means that there is little or no clay and silt mixed in with the sand. This is not neccessarily an advantage. When making mortar with sand and lime, as oposed to Portland cement, a sound mortar can be obtained with less lime if there is some silt and clay in the aggregate.
Limonite it not a kind of clay but is a hydrated iron oxide, usually amorphous or cryptocrystalline and often closely combined with colloidal silica, phosphates, clay minerals and organic decomposition products. It's a product of the weathering of iron bearing minerals and is responsible for mush of the yellow/brown colour of sand. There's not much limonite in silver sand!
Geological pedant.
It is for insulating renders on houses needing a breathable insulating layer outside.
I never knew that
From my (simple) angle, washed sand has larger sharper bits.
I use it to make motar for stone cladding my walls (with rough stone), where at times there is quite a bit of motar. It makes a stronger "lump" than when using "building sand".
Rick
Never do this. Us proper plasticisers.
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Why? As long as you bear in mind just how little detergent it takes, there's not a lot of difference, only that they don't foam when used to excess. Plasticisers are natural by-products of the wood pulp industry in case anyone thought they were some nasty modern invention.
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It's the only time I've seen oxides freely suspended in water, which suggests the particles must either be incredibly small, or they are balanced by some or all of the combination products above. If the oxide content of limonite were higher it wouild presumably have a commercial value as an ochre.
Any geologist is better than none.
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I used sharp sand to bed the shower tray BUT couldn't get the tray to bed evenly so scraped it all off and tried again with builders' sand - no problem.
Dave
I've been known to suggest that oil deposits are the disposable nappies of a lost civilisation.
OK so the silica in glass is in mixture with other chemicals which lower its fusion temperature and prevent it forming back to small particles on cooling? It is not strong as silica grains in sand.
Is the strength of silica grains a limiting factor in the properties of the sand?
I continue to ask as my local council has a problem disposing of coloured glass, it going to landfill. There is a market for clear glass but even this does not cover collection costs if my local authority is correct.
AJH
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