Rice Husk Waste is a Class 1 Insulation material

Extract from
http://journeytoforever.org/at_woodstove-allen.html
Rice husks is a Great Insulation material and can be used as a Building material.

Rice husks are probably the most under-utilised resource available on the planet today. They are very high in silica content and, if the ash is prepared in the manner described in the attachment, a high quality amorphous silica is obtained in the form of lightweight "bubbles". Using a volume ratio of between 3:1 to 12:1 ash to cement, a range of insulating (and refractory) bricks can be cast. In Indonesia and Thailand, we have made low-cost stoves from blocks of this material cast into quite complicated shapes. One useful feature is that like their more expensive cousins, the blocks are soft enough to shape with a hack-saw blade after they have hardened.

Obviously the mechanical strength of such blocks is not particularly high (although the lower-ratio RiceHuskAsh/cement blocks are definitely stronger). And because they are made of amorphous silica, they can only be used up to about 1100 deg C. They have then started to crystallize to alpha or beta quartz. (Even higher temperatures produce crystoballite and tridymite which usually make the block lose its mechanical strength).

To summarise: Rice husk ash gives a range of good castable insulating and semi- refractory blocks when mixed with cement and water (12:1 to 3:1). The practical temperature limit of such cast blocks is probably about 1100 deg C. They have little mechanical strength but are very easily shaped. Dust and water control problems can be easily overcome with a little experimentation.

From the information above, we understand that there is a underutilized resource available

Information provided by
www.supertimber.com
Specialist in Rice husk Waste Utilization