As I think about this (surviving on the Moon)– it’s going to be a mixture of our highest-tech & our lowest-tech.

I don’t have a good idea, of what’s involved in “digging” on the Moon, and I’m really fuzzy on the geology, or how many Earth-equivalent-man-hour’s-of-labor you can get out of a person, in a spacesuit.
I do think the Polymer Science people should team up with the Lunar Geologists, and invent a workable substance to use as a basic building material.
(A substance that cured itself by exposure to a vacuum, for example, would be ideal.)

Make them 20 foot in diameter.
Attach the deflated pipe liner to an airlock at the entrance to a tube just smaller than the tube is inflated.
Inflate the tube and use UV light to cure it hard. You can even mold in ribs to help keep the tube rigid.

You could keep the far end from curing by covering it from UV light. Move in another airlock and attach it to the far end. Then cure it hard.

Keep doing this until you have all the room you need.

IMO you’re on the right track. As to how stuff-like-that, actually gets manufactured on the Moon, I would look toward pre mass-production methods and see if any of those processes or parts thereof, could be adapted.

I’m envisioning that we first get a foothold with stuff-we-bring, then make the most basic materials we can get away with, using the lowest/least complicated technology that works, then start getting more elaborate and advanced.

“Aggregate,” is the most basic building material and one which we use massive amounts on earth.

It won’t be Little House on the Prairie, with sod houses, but that is precisely the sort of thinking we need. Utilize as much as is available on the Moon, with the lowest Tech that does the trick.
If we approach this as “just transferring our modern lifestyle,” to the Moon, it’s not going to happen any time soon.

We need water, oxygen, and electricity. Structures will need to be built– survival structures, they don’t have be pretty or shiny, just airtight and functional.
(There won’t be granite countertops or carpeting, not on the first wave.)

Something like that…

https://youtu.be/t6FWPTZjwLo

Any thoughts on a more crude approach? (lava tubes aside)
I’m thinking along the lines of a more temporary nature to start.
Can we collect & mix the fine Moon “dirt” with some polymer chemistry, and produce a cement type substance?
Take LocalFluffs inflatable module, and cover it with this substance to make a more rigid structure, then commence with your entire plan, as equipment arrives and surveys have been made.
(My G-Father was an actual Civil Engineer, but I only play one on the internet.)

Cotour– I’m leery of the “cold fusion” stuff, but I will check those links more closely and see what he says.

“Inflating a tent inside a lava tube might be a good idea, but I fear that it might be lethal to inhale the regolith. Like breathing shattered glass.”

One of the best things about lava tune caves on the Moon is that there is no known transport mechanism for lunar fines to get into the tubes much beyond the entrance floors. Keeping the dust out of the cave would require a protocol and equipment at the entrance, but electrostatics+ charged Oxygen should help remove it from spacesuits. This is, BTW, yet another good reason to have the initial settlement inflatables hanging from the ceiling instead of on the floor. Any dust drops, and won’t reach the settlement’s equipment inside the tube.

Later, the tubes can be sealed and kept clean in the pressurized interiors by locks and cleaning protocols.

“I know this would be expensive to launch but I find that it is a very strong and interesting material that when mixed it begins to set in 5 seconds.”

When you can get sealing material on the Moon itself, and you can, the cost seems redundant. The lunar regolith outside the cave is basalt. Regolith fines are highly shattered basalt. Their Iron Oxide content is high, and they also contain native Nickel/Iron particles recondensed from impacting Nickel/Iron meterorites vaporizing. These can be removed with a magnet. The basalt’s Iron Oxides can be reduced with Hydrogen that gets recycled.

Plop them all into a low temperature Mond Process reactor to make Iron Pentacarbonyl and Nickel Tetracarbonyl out of them. Distill those to separate them. Then precipitate them as very tiny metal powder particles, as has been done here for over 100 years.

Now, charge the individual metal particles and accelerate them to several kilometers/second in the vacuum of the lava tube cave till they impact against the wall and splatter each tiny particle into a thin flattened layer of metal. Use the Iron powder first, since it is most plentiful, to fill the cracks in the lava tube wall. It *will* have cracks. *All* basalt cracks as it cools!

Then do the same, using the Nickel powder, to thinly coat the Iron sealant layer, to keep the moisture breathed out from the human bags of water from corroding the Iron. Finally, the waste from the basalt reduction process will be enriched in Aluminum Oxide and Silicon Dioxide. Powder this, and again, electrostatically spray that powder at several kilometers/second into the Nickel layer coating it so that it is separated from the percentage of humans who have an allergy to Nickel. This will turn the walls white from the oxides.

Now, use the white walls of the lava tube as a projection screen on which, using lasers to project them, you will have scenes from outside the tube on its surface. Everything from lunar surface and star views to Jupiter’s bands and Saturn’s rings to scenes of green Earthly valleys can be used at one time or another.

Nothing need be brought from Earth after the first several tons of chemical processing equipment and accelerator parts. Not only that, but those several tons of processing equipment can be set up at many lava tubes over time, instead of their costs being assigned to just a single lunar settlement.

It was received here with a healthy skepticism, as it should be. But the system testing appears to be continuing and does seem to be viable. Look it over, see what you think.

But, I will take a deeper look, later tonight.

tangentially–
You might like some of the stuff the “National Ignition Laboratory” works on—
https://lasers.llnl.gov/

They’ve been working on fusion energy for some time. They use lasers & magnetic containment. So far, energy-input is less than energy-output, but they are making progress, albeit very slowly.

https://youtu.be/3mrGT_fOd1o

http://www.e-catworld.com/

http://www.e-catworld.com/2016/09/30/rossi-reports-recent-tremendous-progress-with-e-cat-quarkx/

Might it be tested on the moon?

My casual impression is that lava tubes are not very interesting from a resource utilization point of view. That volatiles are not expected to be found there. Because the lava flow that created them removed them. But on the other hand they should be as great cold traps as polar craters are, so I don’t really understand this.

Putting humans in a cave that hasn’t changed in four billion years, humans with their heat and movements and gears, that might cause it to collapse (maybe one could just catch the slow boulders falling down from the roof with the hands in that low gravity…) The Moon has a “geology” which is yet poorly understood. What looks like free housing could be a death trap. So I think that Lunar lava tubes are good for later on missions and not a resource for the first campaigns. But an intriguing science target for sure. And visiting a huge sealed cave in the Moon naked (or almost for decency’s sake), breathing oxygen and touching its surface with your bare hand, how cool wouldn’t that be! Grabbing the wall and talking to the echo of the chamber:
“- I am the master of the Universe! I came and conquered. I am human, you are my property.”

You’ve probably encountered examples of structural-reinforcing in this manner, throughout NYC. When they rehab those 100 yr old brick building’s, they seal everything with chemicals such as the LineX stuff, protects against degradation & imparts some structural stiffening, depending on what formulation they use.

As to the pesky details of spraying stuff like this, in zero G or a vacuum, I must plead ignorance.
I would guess– formulation would be the key engineering factor.
They are all just various combinations of polymers and aromatic hydrocarbons, and I don’t have a good idea of how those substances behave in Space.

It is, a Great Idea. Seal up the interior of some of these lava tubes, and you’re in business.)

https://youtu.be/GVKhrrJ4fCU Line X bed liner coating used for other applications.

https://youtu.be/Lfd7_p4SVBU