Papercrete (Hypertuffa) water exposure?

I know about papercrete. I have worked with it experimentally/small scale. I have friends who swear by it.  All seem to think it is the universal wonder - which is why I suspect it.
Hypertuffa is also interesting, but will not last, as the organic matter in it adds to its deterioration, especially when exposed to water or high humidity.
Papercrete, like it or not, has organic matter in it as well.  If I were to build a partially underground wall with it, and there was a particularly wet rainy season, or it was in dirt that was normally very moist, or used for the wall of a pond or pool etc. I think it would over time deteriorate, as there is no avoiding some paper fibers being a part of the exterior surface of any brick or wall - thus possibly letting in, or even drawing in water/moisture.

Does anyone have first-hand knowledge or experience with papercrete exposed long-term to water?
What are the oldest constructions made with it, and how do they look, how are they holding up?
Also - is there any reliable figure for how much papercrete weighs per cubic foot ?

I think that the weight will depend on the mix used, and that likely depends on the conditions for which is intended. Some papier Mache can be extremely light but very very strong (usually with some sort of frame tho if a larger piece)  but as anyone knows who has moved boxes of books, paper can also be damn heavy.

I assume you have looked through the papercrete site and links. There's lots of good info on there.

Paper would be pushing it as a foundation imo  because it would have no way to get rid of the moisture it took in. People who have tried to make paper mache statues for their gardens have seldom been happy with the results over time when they are left out .OTOH there is a site which details  a very successful business which operated for a number of years building boats made of paper, everything from racing shells (which were enormously successful) to pretty big  boats. For a number of years observatory roofs in a number of universities were made of paper mache, some of them in places like the midwest US and Scotland,so  they would have had some difficult weather to deal with.  And at one point   the wheels for railway cars were made of paper. I believe one such is in a museum in the midwest somewhere.

There is a guy I think around seattle.selling plans for making a cardboard boat..it's been a while since I saw that site; he had a couple of videos on You Tube of people paddling happilly around a bay.

It's a matter of dealing with the realities of the material in the context  it seems. Also, both paper and glues have changed considerably in the last hundred years, not always to the better. Many of the glues used to accomplish the wearability of the paper constructions were a trade secret and their manufacture died with their inventor.For example, the glues used in Stradivarius  violins is now largely regarded as being a major factor in the spectacular tone so much research has gone into trying to learn which resins and so forth he used. Most glues have not had that attention.

Hypertufa is frequently used for "rock gardens" and seems to last a long long time even in situations where it is constantly exposed to weather and damp soil, if it is properly cured. It is certainly possible to crack it with freeze/thaw but that's the concrete in it, not the organic material as concrete cannot adjust as organic material can. Same reason that concrete foundations sometimes develop leaks , to my understanding, if not well waterproofed.

Buildings made from organic material are still standing after hundreds of years so if well built will last long beyond your life span:).

I don't have any experience with papercrete but I like the idea of an insulated concrete using vermiculite mixed in with the concrete. I believe they talk about/use it in the book "Building Green", but caution that it loses some of its structural strength so not to use it for foundations or piers.

On another note, I am about to start building on my house using a fascinating product called Faswall. It is a type of ICF made from cement bonded recycled wood fibers, pressed into a block. It comes with insulation on the inside, either mineral wool (R-21) or polyiso (R-26). The blocks are 12"w X 24"l X 8"h and are notched horizontally, as well as having the normal CMU-type vertical cavity, so when they are filled the concrete forms continuous horizontal and vertical grids. Siding or stucco can apply directly to them ( its wild, you can screw right into them with wood screws!) yet are hygroscopic (vapor permeable). I'm excited to see how they are to build with/live in, I will post some photos as things progress, still working on the footings right now.

For use in a roof, I am thinking about maybe a fancy form with a two or three part process;
The first part would be a form that has many squares within/on it, leaving the areas for some kind of strong-formula reinforced concrete, and maybe mesh spanning the whole thing.
The resulting actual concrete would be a skeleton or frame of criss-crossed ribs.
The second part would be to fill all the square holes between the ribs with an ultra-light reinforced mix of papercrete and perlite, or similar. Thus having the benefit of solid reinforced strength, and still making it lighter than solid regular concrete - and then sealing the whole thing somehow.
It could be a time consuming process, but maybe well worth it for the resulting quality and usefulness.

This guy has done lots of building with lightweight concrete, although I think likely not with paper involved. His designs are quite extraordinary..art really.
http://www.flyingconcrete.com/