[GSBN] prefab strawbale - pinning (fully baked)

[martin hammer]

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.
> 
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