Environmental Engineering Reference
In-Depth Information
watched those with more advanced tacit knowledge skillfully use a chain
saw to cut difficult angles on custom bales and to cut recessed arches into
the straw wall to be plastered over, becoming niches, part of the southwest
aesthetic. All this took place in the two weekends that I participated in two
wall raisings.
Visits to subsequent sites and conversations with owners and builders
informed me of techniques to contend with moisture protection in the
humid and rainy climate of central Texas.A much-told story concerned the
importance of breathability for finished straw-bale walls. A client of one of
the local straw-bale builders had gone against his advice and painted his
walls inside and out with Elastamerica paint, which completely seals a sur-
face with a plastic-like coating.With the walls completely sealed, tempera-
tures varied widely between the inside and the outside. In summer, when
air conditioning was in use, condensation built up inside them, making the
bales wet and contributing to bale rot. If breathable natural plasters are used,
such condensation will not occur.
The wall raisings in which I participated in Texas did not reach the state
of completion for plastering before I left for Washington, so I only knew
about the techniques from the small introductory workshop at the first site.
There I learned about “robert pins” (the “grown-up bobby pins” used to
fasten wire lath to the bales for rounding out window and door frames, cor-
ners, and other architectural details), and I learned that plaster (in amounts
ranging from one scratch coat to three coats) is used to seal a straw-bale
structure from the elements, including pests.While I was attending the first
Natural Building Colloquium East (held in Maryland), I finally had the
opportunity to pick up a trowel, helping finish a straw-bale garden wall.
Tacit knowledge here starts with understanding the use of half a dozen dif-
ferent kinds of trowels, developing a technique to work the cement plaster
scratch coat, the first applied, into the straw instead of leaving an air gap
where the wire lath may not be flush.This mattered only for aesthetics and
durability for the garden wall, but on a house an air gap with metal present
could significantly lower the insulation value of the wall.This is a lesson the
Department of Energy learned when they first set out to test straw-bale
walls and found them not up to claims because they had built the wall
incorrectly. (Fortunately, they rebuilt it, paying attention to the air gap, and
came up with numbers that matched those of the claims made by the straw-
bale community.) The final tacit skill lesson, which I was not ready to learn
until I had worked with the tools and the medium for a while, becoming
