Together with ABARI, Open Biotecture worked on natural waterproofing using resin. The idea came to us, at our first meeting, that waterproofed rammed earth could be a great substitute to cement or concrete for water tanks and wells, which are commonly used in Nepal and elsewhere. Waterproofing rammed earth or clay, can also be used in many other construction applications.
At first we thought of using glazing, traditionally used for pottery. However firing large structures such as wells would embody much energy and obtaining an optimal and even temperature to fire the glazing would be too difficult a task, probably resulting in unwanted cracks. We found out later that resin or molasses have been used to waterproof pottery, this seemed a good alternative as resin melts at much lower temperatures.
Here in Kathmandu resin can be easily found in shops selling religious ritual items. The resin called saalko dhoop is a form of frankincense or myrrh which is collected from the saal tree. We bought some of this resin and ground it to power, spread it over some clay shard and heated the shard on a conventional kitchen stove. The resin melted and was spread to different thickness over the shard.
The result was astounding. Once the shard and resin had cooled down, the shard was completely waterproofed and the resin adhered perfectly on the shard, especially where it had been laid down thinly.
In our enthusiasm we bought more resin to apply to some rammed earth and mud plaster samples. The process however was much more disappointing: when the hot resin is applied to a cool surface, it retracts before it can adhere. The resin then is thick and brittle. We surrendered to the conclusion that applying the resin to rammed earth would be impractical, we would have to heat the rammed earth mass to allow adhesion, which would be too energy consuming.
However we have not given up. Just as the resin was applied on a clay shard, it could be applied on a sun-dried clay roof tile or on some bamboo shilling. As to waterproofing rammed earth so as to build a tank or well, more ideas have to be tested out: applying wax or oil would probably work. More experiments await us.