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During Greg & Raquel's baleraising this
weekend, Joe McCabe commented on how we were using mud in sealing up the bales,
and I realized this had become a standard practice for us but that I'd never
fully shared it with the list, even though they've all been discussed at one
time or another. The baleraising was--as all baleraisings are--a great
time. Greg and several of his family are rice growers, so there were
plenty of people around who were handy with bale hooks to stack bales. In
an irony typical of baleraisings, Greg's surgeon brother ended up on chain saw
duty, notching bales, and a local pediatrician spent her time at the event
mixing mud and straw with her feet.
The mud mixing arena was very popular with the kids
under 12 and the moms, and they kept us well supplied. We've taken to
using mixes of mud and straw extensively in a couple of ways in order to reduce
air and water inflitration into the bales. The idea is that mud and straw
provides a better seal for gaps in the bales than packed straw alone. Mud
can lubricate the straw, making it easier to fill gaps, and of course the mud
itself also oozes to fill little spaces that straw wouldn't. The straw
provides strength and binding as well as insulative value to the
mud.
Rather than stuffing the gaps between bale ends
with loose straw, we make a fairly wet mixture of straw and mud--wet enough to
work with gravity--and stuff/pour it into the wall before stacking the
course above. Because the ends of bales are not flat, but pillow out
between strings, these gaps can be significant.
Before applying lathing, we also fill any gaps on
the bale surface, both inside and out. For this we use a higher proportion
of straw and less water so that the mix will stay in place with less
cracking. In doing this we are sealing the gaps in the bales from air and
water intrusion, and we are also making the surface of the bales flatter.
Stucco shrinkage will be different for different thicknesses of stucco, and so
cracking can occur along lines where the thickness of the stucco varies
markedly--such as often occurs along the lines between the bales, around posts
or other gaps. Filling these spaces with mud assures that the stucco layer
will be of more uniform thickness.
The third way we've been using mud/straw has been
to provide a thin mortar bed between bales. For this we use a medium-wet
mix with chopped straw and slather it on top of each course of bales. The
mix should be thin enough to flow and fill small gaps in the bale "fluff", but
not so thick that it would keep the next bale from seating directly on the straw
below it. This mortar is very effective structurally: it increases
shear friction and, when properly done, is about 80% as effective (after the mud
dries) as compressing bales for stiffening the walls.
Finally, we will sometimes us a thicker layer of
mortar--mostly straw with a little mud--if we need to increase the height of a
wall a little. A thick mortar bed will weaken the structural and shear
capcities of the wall, so this should be used only in areas, and thickness of
less than an inch or so, where this will not be significant.
Sealing the bales with mud is cheap, easy and
fun---and significantly improves the thermal, moisture and structural
capabilities of a bale wall, and has become a standard procedure for
us.
John
John Swearingen
Skillful Means--Architecture and
Construction
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