On Thu, 01 Sep 2005 22:36:23 +0100, Andrew Gabriel
wrote:

BTW thanks for your comments and your FAQ which I browsed before
starting. One area in which it seems very difficult to get much hard
advice is the sand/cement ratio, type of sand, and other additives
for any given application. I think I had ratios between 1:2 and 1:4
suggested. My roofer tells me they used to use 1:3 for this, but
nowadays it's done with 1:4 using a 50/50 mix of building sand and
sharp sand. It would be good to see a chart somewhere ranging from
the strongest through to the weakest mixes, and typical usages of
each.

1:2 is a bit too strong, with the risk of shrinkage. Bearing mind that
most mortars are gauged bt volume, either shovelfuls or bucketfuls, rather
than by weight, the mix ratio will by nature be approximate. Fortunately
mortar is quite tolerant to exact ratio. As for the chart, that is a very
tall order. Admixtures, water ratio and the particle size distribution and
shape (rounded, subrounded, subangular, angular) all play their part. I
did try writing a program to analyse this, assuming spheres (the simplest
maths, but still brainpain)but that was when I only had BASICA, this being
before Live Aid had even become an idea. In the end it was down to trial
and (mostly) error. There was a company which supplied monotypical (same
size and particle shape) sands, but they appear to have gone under. In the
end the project I was working on struck gold. There was a company which
used cyclones (think a ginourmous Dyson) to grade sands and one of their
products was perfect for the application. The boss thought I had rigged
the results at first until he himself made and tested the development
product. He was as gobsmacked as myself. Market leader in six months. I'll
have a look in Fry's to see if there is any guidance. Cover price £70,
picked it up for 30p. :-)

John Schmitt

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