Re: SB: Fly ash

[John Kingsley <johnk@magma.ca>]

Keith,

> ps.  I tried asking before, but nobody gave me a solid answer....for the
> recipe for portland cement stucco.  Is it 4:2:1  Sand:Portland cement
> powder:lime, along with a squeeze of dish soap.....and water (of course) to
> desired consistency???  How does that sound?

There are 2 ratios to worry about:
1)  sand : cementitious material (portland cement and lime)
and
2)  portland cement : lime

Ratio 1) affects cracking (among other things). For 1) you
have 4 : 3 (2+1).  This is almost 1 : 1 - very, very rich!
You need more sand or you will end up with lots of cracks
(not to mention it will be more expensive).  More standard
ratios are 3 or 4 : 1.  Suppose you choose 3.  Then your
overall ratios become 9:2:1.  If you choose 4 your ratios are 12:2:1.

Ratio 2) affects vapour permeability (among other things).
For 2) you have 2 : 1.  I would suggest decreasing
the cement.  There has been some research
that indicates a better ratio is 1 : 1 in terms of
vapour permeability.

On my place I used a ratio of 6:1:1.

cheers,
John

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