I winced when I watched this video titled “Trimming the Fat” about how the folks at Konbit Shelter were using a machete to cut off the poly bag material and some of the stabilized fill to smooth out the interior wall of a dome they have been building in Haiti before plastering.
I suppose I shouldn’t be surprised at this practice, since Nader Khalili and the folks at CalEarth Institute have long maintained that once the fill material (adobe soil or cement stabilized soil) has set up, the polypropylene bag material is unnecessary. I remember touring the CalEarth demonstration compound and seeing lots of tattered, sun scorched bags flapping in the breeze. I have even noticed that some CalEarth trained people will use a torch to burn off the exposed bag material, believing that the plaster will bond better with the hardened soil.
The problem is that this practice would not only weaken most earthbag buildings, it could lead to collapse, especially if the fill were at all loose. Even with stabilized soils, the bags provide a great deal of tensile strength, something that the fill specifically lacks, and in a seismic event this could spell the difference between wall failure and not. I consider the earthbags themselves to be an integral part of the whole system, and caution people to always protect them from sun exposure, and abrasion.
We don’t really know how long polypropylene will last if protected from the UV in sunlight. One report said 30-year-old polypropylene bags were recovered from a landfill (which is approximately how long poly bags have been in existence) and they were still in good condition. Another study concluded that the half life of polypropylene fabrics in benign environments could be 500 years or more. We know that moisture does not seem to adversely affect the poly material.
So please be kind to your earthbags so they can continue to be a structural part of the building!