[GSBN] moldering straw question

[bob at bobtheis.net]

Hi All, 

I’m passing along a query from a fellow CASBA member here: 

I came to a straw bale building project that was already in progress.  Several weeks prior to our arrival a workshop had stacked, meshed, and plastered (with NHL) part of the building, and the owner dutifully kept the walls shaded and damp for two weeks after the plaster was applied.  Too wet as it turns out.  An accidental roof leak six weeks after the walls were plastered lead to us probe the walls in the vicinity of the leak and we discovered a much larger problem.
 
Even though the weather had been hot and dry, moisture readings taken through the unplastered interior walls showed high moisture levels (well above 30%) along the exterior of all the straw bale walls, not just the small area where the roof had leaked.  Moisture appears to have been at this level for a month to six weeks before we discovered it.  Removing small portions of the scratch coat revealed that straw within a few inches of the exterior bale surface has begun to decompose.  Removing larger portions of the scratch coat confirmed that the damage was extensive, and probably impacts all of the plastered walls.
 
Questions:
 
1.       If a straw bale wall has been overwetted like this, which has caused several inches of the exterior straw bale surface to partially decompose (straw stalks still intact but discolored—greenish black and grey—and with somewhat reduced tensile strength), at what point is it best to strip off the plaster and mesh and start over with new bales?  So long as the bales don’t handle roof loads, resist lateral forces, or act as the primary lath for plaster, what are the trade-offs in leaving the wall assembly as-is, with several inches of partially decomposed straw on the exterior bale surface?  What are the performance costs?
 
2.       Indoor air quality concern.  If a decision is made to leave the bales in place, re-plaster them, but follow better guidelines for keeping the NHL walls damp (not wet enough to wick!) during the curing process, is there a concern that the now much higher mold population poses an indoor air quality risk, or that the more numerous mold spores will more easily re-activated should wall moisture conditions permit?  If so, does anyone know of or tried methods to remove or neutralize the mold prior to re-plastering?
 
Many thanks for your experiences and speculations!
 
Jim
 
Jim Reiland
Many Hands Builders
541-899-1166
541-200-9546 cell
jim at manyhandsbuilders.com <mailto:jim at manyhandsbuilders.com>
www.manyhandsbuilders.com <http://www.manyhandsbuilders.com/>
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