"Dave" wrote in message
...
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.