Idea:
You can buy filaments for 3-D printers that allow you to print dissolvable 3-D printed supports:
http://www.3ders.org/articles/20160428-kai-parthy-is-back-with-lay-away-series-of-soluble-support-filaments-for-fdm-3d-printing.html
This allows you to print 3-D objects with overhangs, nested objects, and hollow objects.
However, for large scale structures the size of a house, PVA may be too expensive as a soluble support material.
But what about sand? Here's a patent on making sand sculptures with a water soluble adhesive:
Composition and method of forming sand sculptures
"A sand sculpting composition including approximately 100 parts by dry weight of sand, between 0.1 part and 5 parts by dry weight of at least one non-toxic cold water-soluble adhesive agent selected from the group consisting of pre-gelatinized starches, chemically modified starches and chemically modified celluloses, and between 6 and 25 parts by weight water. The adhesive agent has been combined with the sand and an amount of water sufficient to both dissolve the adhesive agent and allow the adhesive agent to coat the particles of sand. A coloring agent may be added to the adhesive agent."
https://www.google.com/patents/US6899755
So, you build up your structure with a nozzle connected to two tanks, one dispensing sand+adhesive and one containing cement+basalt fiber roving. The nozzle switches between the tanks depending on whether you're printing permanent structure or temporary support.
Then, once the permanent structure has cured, you use a pressure washer to dissolve away the sand supports.
You can buy filaments for 3-D printers that allow you to print dissolvable 3-D printed supports:
http://www.3ders.org/articles/20160428-kai-parthy-is-back-with-lay-away-series-of-soluble-support-filaments-for-fdm-3d-printing.html
This allows you to print 3-D objects with overhangs, nested objects, and hollow objects.
However, for large scale structures the size of a house, PVA may be too expensive as a soluble support material.
But what about sand? Here's a patent on making sand sculptures with a water soluble adhesive:
Composition and method of forming sand sculptures
"A sand sculpting composition including approximately 100 parts by dry weight of sand, between 0.1 part and 5 parts by dry weight of at least one non-toxic cold water-soluble adhesive agent selected from the group consisting of pre-gelatinized starches, chemically modified starches and chemically modified celluloses, and between 6 and 25 parts by weight water. The adhesive agent has been combined with the sand and an amount of water sufficient to both dissolve the adhesive agent and allow the adhesive agent to coat the particles of sand. A coloring agent may be added to the adhesive agent."
https://www.google.com/patents/US6899755
So, you build up your structure with a nozzle connected to two tanks, one dispensing sand+adhesive and one containing cement+basalt fiber roving. The nozzle switches between the tanks depending on whether you're printing permanent structure or temporary support.
Then, once the permanent structure has cured, you use a pressure washer to dissolve away the sand supports.