Cool, that's a third of my wish-list ticked off
In case anyone's wondering, the other two are specialized materials, which looks like a definite as well, and hexagonal 'bricks' - these act as minerals that cluster together. With specialized glands, a bot can dissolve these for minerals (shell etc.), and regurgitate them. This would be a sort of abiotic factor in the environment to interact with that would allow bots to build shelters or hives.