Rice hulls

How long can rice hulls last? Will they deteriorate or decompose if they are used in earth bag construction?

I would coat them in clay slip. Some diatomaceous earth might also help. Moisture is the real killer.

Like any botanical fiber...if they stay "under water" they can last a very long time...but for building...anything above 20% humidity can lead to rapid decay and fungal activity. So for a wall matrix, I would only use them as a replacement for straw or wood-chip in a clay slip of perhaps in a cobb matrix. Bag forms in a "poly bag" not "sisal or hemp" natural fiber bag gives me pause because of the thickness and potential for interstitial moisture buildup as well as the poly bags not being as breathable as natural fiber and/or creating a "condensing surface" being a plastic. That would be my, off the top of my head, thinking...

For my own information, I compared the water absorption of rice hulls, straw and wood shavings by soaking them in separate plastic cement trays for 3 days. The water could be poured off of the rice hulls leaving them barely damp and they dried out completely and quickly with no odor. The straw absorbed most of the water and didn't dry out and smelled of rot. The shavings retained all of the water, didn't dry out and had an off odor. According to Wikipedia, the r-value of rice hulls is 3 per inch.

Here is some more info:
http://www.appropedia.org/Hullkrete_and_fiber-crete
https://earthbagbuilding.files.wordpress.com/2012/01/rice-hull-wall-section.jpg
https://en.wikipedia.org/wiki/R-value_(insulation)