Shell worlds

> , perhaps spray some sort of sealant on the inside walls, and pressurize the whole thing

I heard an interesting assertion in regard to this. Someone once argued that if pressurizing a lava tube with a breathable atmosphere, the walls would become sealed without any extra effort. It was pointed out that just a few feet below the surface, the temperature of the lunar soil is permanently below the freezing point of water. A breathable atmosphere, by necessity, must have a component of water vapor. It was argued that water vapor, once having penetrated a certain distance into the cave wall, would freeze into an impermeable barrier.

Regards,
Mike Combs