[GSBN] prefab strawbale - pinning (fully baked)

Tue Aug 11 14:29:20 UTC 2009

Martin,

I think you've covered most of the variables such as the integrity/height of
the bales, the strength of the mesh, strength of plaster, and design loads
on the wall.

However there's something implicit that you've discussed that we should pin
down a little better, and that is that there is a major difference between
driving pins inside the bales ("internal pinning") and tying them to the
outside ("external").

Internal pinning is difficult, (unless you have testosterone charged guys at
your workshop with nothing else to do), and much less effective.  This can
be easily verified by kicking a pinned bale out of place--it's not so
difficult, as the bale can be forced to shift around the pin without extreme
force.  That's not the case with external pins, strapped hard against the
exterior face of the bale.  The bale will not shift around the pin; the
stiffness is limited only by the rigidity of the pin/mesh/tie assembly.

(There is a problem that I think can result from external pins, which is
that the thickness and integrity of the plaster skin may be interrupted by
the pins--a chance for cracking to occur).

The other advantage is that pins on both sides of the wall, separated by a
distance and embedded in plaster, work to create a more stable, stress-skin
sort of panel.  When mesh is used the most important function of external
pins tied through the bales is not stiffness, but to resist delamination of
the skins.

Pinheads swear by external pinning and do it all the time, but we've
actually never bothered to do it.  With the mesh we use (2"x2" x 14g), and
the solid bales available to us, we can  just tie mesh on the two sides
together with 14 g wires. We have only used pins in Xtreme Strawbale (TM),
when the forces were so great that the wires would have ripped through the
mesh; in that case we attached the mesh to short dowels, kind of like
washers, over the mesh on each side.  Our skins are so strong that they will
carry the loads as long as they don't buckle and delaminate,

Pinheads seem to focus on stiffness, but that's rarely an issue for a
modestly designed bale wall with good bales and plaster. Without getting
into psychology, you could say that, "size" matters, but "stiffness" is not
an issue.  Pinheads do it with bamboo; we're into making a big mesh.

I'll leave it at that....

John "How stiff do you want it?" Swearingen

On Tue, Aug 11, 2009 at 1:35 AM, martin hammer <mfhammer at pacbell.net> wrote:

> I sent the half-baked e-mail below by mistake, so I'll put it back in the
> oven and add to it:
>
> On 8/11/09 12:40 AM, "martin hammer" <mfhammer at pacbell.net> wrote:
>
> > Nice to hear from you Andy.
> >
> > I and many others have found that in addition to being time consuming and
> > costly, pinning doesn't provide much benefit after the plaster is
> complete,
> > so many of us (in the US and Canada) (and elsewhere?) no longer use pins,
> > especially internal pins.
> >
> > But there are many variables and reasons to pin or not to pin, and I
> don't
> > believe the issue is entirely settled.  Some thoughts:
> >
> > One theory is that pinning provides stability to the stacked bales before
> > plaster, but that after the plaster has sufficiently cured and/or dried,
> the
> > plaster takes over and does some or all of the work that pins do in an
> > unplastered wall.  So, if you can keep the stacked bales where you want
> them
> > without pins (usually the case with bales laid flat, not tall walls),
> then
> > don't pin, just plaster.
>
> With the theory I described, there are questions about how "strong" the
> plaster needs to be in order to make pinning unnecessary.  Does the plaster
> need to be reinforced?  If so, what type of reinforcement?  What type of
> plaster?
>
> It's actually more than theory, because a number of unpinned plastered
> walls
> have been tested (see Bruce King's book) for both in-plane and out-of-plane
> loads.  Walls with different plasters, mesh, and detailing.  Even the
> relatively weak walls fared well (enough) without pins.  But there's the
> question of how strong a wall (in given conditions) needs to be to resist
> legitimate design loads.  This can usually be achieved without pinning.
>
> However there are situations where pinning might be the best way to go, or
> even necessary.  I've used pins (internal or exterior) or "staples" as
> needed to keep a wall or parts of a wall stable until it's plastered.  Or
> when dealing with extremes, like tall thin walls, then pins (especially
> exterior pins) are a good way to resist buckling due to gravity or
> out-of-plane loads even after the plaster is in place.
>
> The Pakistan wall system, with its 1' wide bales stacked to an 8' height,
> really need the opposing, thru-tied, exterior bamboo pins to keep the walls
> stable before plaster.  But they also do great service AFTER plaster to
> resist out-of-plane loads in an earthquake, as I witnessed during the shake
> table test.  I believe (but can't yet prove) that they kept the bales on
> the
> foundation during the most violent shaking, and that the nylon mesh alone
> wouldn't have done so by itself.
>
> There are other things to consider and say about this (or better ways to
> say
> what I've already said), but I'll stop there and let others chime in if
> they
> like.
>
>
> Martin Hammer
>
>
> >
> > On 8/1/09 11:57 AM, "Andy Horn" <andy at ecodesignarchitects.co.za> wrote:
> >
> >> It was mentioned that the Balers in the US no longer bother pinning
> their
> >> bales unless a building code necessitates it. Are you no longer finding
> it
> >> necessary to pin because you are doing structural mesh reinforced
> plasters
> >> and find it unnecessary...or because you are doing a lot of load bearing
> >> with heavy strapping so find it not necessary?
> >>
> >> We still pin our bales, though not from the bottom any more as this is
> in my
> >> opinion/experience unnecessary and I would say indeed unwise as it can
> only
> >> encourage condensation.
> >
> > _______________________________________________
> > GSBN mailing list
> > GSBN at greenbuilder.com
> > http://greenbuilder.com/mailman/listinfo/GSBN
>
>
> _______________________________________________
> GSBN mailing list
> GSBN at greenbuilder.com
> http://greenbuilder.com/mailman/listinfo/GSBN
>

-- 
John Swearingen

Skillful Means
www.skillful-means.com
blog: https://skillfulmeansdesign.wordpress.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.sustainablesources.com/pipermail/gsbn/attachments/20090811/2f45bd54/attachment.htm>