Sodium Silicate (known as water glass) is a valuable, as well as interesting, material. Able to withstand high temperatures, it's used as an automotive stop leak, as well as furnace cement, to repair cracks in cast iron stoves. It can also be used to produce a structural foam. On earth, it foams and drys when poured onto moulten lead, or when heated with a magnifying glass or large Fresnel lens. It also foams when exposed to a vacuum, due to low temperature boiling. This process results in a hard, glassy, outer shell. Here's a source document:
Sodium Silicate as a Versatile Structural Material:
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&cad=rja&uact=8&vedFwQFjAI&url=http%3A%2F%2Fcontrails.iit.edu%2FDigitalCollection%2F1965%2FAFAPLTR65-108article14.pdf&ei=nNb4VPigMI-yoQSgkoHQAg&usgQjCNEc2Q5c5LDXyoXlZXK1yLUZbXuRyQ&bvm=bv.87611401,d.cGU
This document suggests coating a string with water glass, then exposing it to the vacuum of space. The string, which could contain a carbon fiber, then becomes strong enough to be used as a structural member. This sounds like the ideal candidate for use with my String Bot idea.
The key to the String Bot is globally positioned 'anchors' placed at strategic locations, such as geodesic vertices, with the Bot then traveling from one anchor to the next, unraveling the Sodium Silicate coated string. The Bot would need to travel directly, in a straight line, as the water glass will quickly start foaming and hardening as soon as it's exposed to open space. The anchors can be held in place with Hall Thrusters, Ion Motors, or any other type of electrically powered propulsion system. Once something like a dodecahedron is created - perhaps with mile long edges - each edge can be reinforced with additional passes of the String Bot. The Bot could even spiral around the first string. Or, an extrusion machine could travel along the stiffened string, building up additional layers of foam. Or laying down concrete or some other building material. Once the edges are strong enough, the String Bot could then inexorably begin wrapping the entire structure, until a completely solid surface is produced.
My original String Bot application idea was to use a quadracopter drone to pull resin coated string between the ends of vertex support poles, to form a dome. But I'd rather build a very large structure in space. Structural foam seems like a doable approach. Anyone interested?