What is the lifespan of poly bags, and will they make durable foundations? From our experience and from what we can gather from other sources, poly bags can last almost indefinitely if kept out of sunlight, and therefore double-bagged foundations appear to be extremely durable. This is important because earthbag foundations are much lower cost than concrete foundations.
One report said 30-year-old polypropylene bags were recovered from a landfill and they were still in good condition. This is approximately how long poly bags have been in existence. We also know from anecdotal evidence that moisture does not seem to adversely affect the poly material even after years of contact with wet soil and natural swings in temperatures, including harsh freeze/thaw cycles.
A Federal Highway Administration (FHWA) study concluded that the half life of polypropylene fabrics in benign environments could be 500 years or more.
[Note: this information is from a GeoMonolith report at GCSwall.com. We would like to find the original FHWA report in order to check the facts. If anyone has time to locate this report, please let us know. You could easily talk me into a free book for your trouble.]
Update: One of our readers who goes by the name Thomas has just won a free earthbag building book. Thomas located the original report we were looking for. Actually, there are four reports that analyze 24 exhumed samples from 12 sites. This government study should provide very compelling evidence about the durability of geosynthetics (poly bags). Thank you Thomas. We’ll get the article and summarize the report here at a later date.