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Re: [SG] Hypertufa stepping stones

On Wed, 27 May 1998, Claire Peplowski wrote:

> In a message dated 5/25/98 9:30:07 PM Eastern Daylight Time, kay@FERN.COM
> writes:
>
> << Besides hypertufa, you can also just pour concrete stones in place...
>  dig a hole about 2.5" deep and the shape you want.  Using a sack of
>  concrete mix (and preferably adding one of the fiber amendments that
>  replace wire reinforcing), pour and level the stone in place.  You can
>  also dust the surface with powdered concrete dyes and/or mix in colorants
>  to make the concrete belongs in the area.  Or you can scatter some
>  of your soil on top and sort of trowel it in a bit... it usually results
>  in a bit of coloration and a slightly irregular surface more like
>  real stone. >>
>
> While this sounds like a simple effective idea, I think in zones 5 and further
> north where deep in ground frost is present in winter months, more care is
> needed to use concrete.
>
> Nearly everything without drainage beneath will heave.  Our area of the world
> is littered with cracked walks, walls and foundations.  Those forms sold in
> catalogs for garden paths do not produce durable walkways in zone 4.

Uh, "stones" I poured almost 30 years ago in Iowa (zone 4/5) are still
intact, though a bit sunken now over the years, thanks to the worm
activity.  Big slabs crack, but smaller pieces, perhaps 1 - 1.5 sq ft,
just ride it out.  The soil is clay, the drainage pretty poor. Those
stones had some coathanger wire in them for support -- the fiber
reinforcement is vastly superior for small projects like this.

I can't speak to the forms, since I've never used them, but I was of the
impression that the net result was not a slab but a number of disconnected
"stones".  Though I'd expect the stones to rise and fall independently of
one another enough to look bad (and be a possible tripping hazard) after a
number of freeze-thaw cycles.  If it is indeed a slab, you need a properly
drained underpinning for concrete, regardless of temperatures.  Ask
the folks in Houston (USDA 8) with cracked foundations from unstable
soils soaking and drying in the summer.

BTW, all concrete will crack eventually, even properly post-tensioned
slabs.  That's why control joints are tooled into the concrete... usually
every 3-4 ft max ... to stop long cracks from running clear across the
slab.

Hypertufa tends to be porous enough that it would be prone to
spalting during repeated freeze-thaw cycles.  On the other hand,
I know of several hypertufa planters in Iowa that get only a tarp
thrown over them in the fall for winter protection... they're
high enough above ground surface that all you have to do is
keep the whole thing dry.

Kay Lancaster    kay@fern.com
just west of Portland, OR; USDA zone 8 (polarfleece)
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