Ground Contact with Papercrete

Kelly Hart, who is your host at greenhomebuilding.com, has been involved with papercrete from the early days of its popularization. He included interviews with papercrete pioneers Mike McCain, Eric Patterson and Sean Sands in the video he produced: A Sampler of Alternative Homes: Approaching Sustainable Architecture. He also chronicled his own use of this amazing material in his video: Building with Bags: How We Made Our Experimental Earthbag/Papercrete House. Kelly has built and used both an electric barrel mixer, and a McCain-designed tow mixer. His house is plastered inside and out with papercrete and can be seen here. He can speak from his experience with this novel stuff, and is frank about both its pros and it cons.

Questions and Answers

Q: Can papercrete be earth-bermed, or is that mixing apples and oranges so to speak?

A: I don't advise berming directly against papercrete, even with some sort of moisture barrier. The papercrete is so it will wick moisture from the ground, and then because it is not exposed to air, it will not dry out readily and will become soft and spongy and might support mold. If you want to earth berm, better to use earthbags or some other stable, mineral material where the earth is in contact, then papercrete can be used above the ground.

Q: Ever heard of papercrete used in ground contact application--i.e. forming sides for raised beds?

A: I know of at least one building that that was made with a papercrete foundation dug into the ground. They would never do it again! Papercrete is like a sponge and will wick water readily. When it is continually wet, it loses some of its strength and coherence, and is more susceptible to mold, etc. I wouldn't recommend it.

Q: I have to 'do' two retaining walls.....something tells me that papercrete won't work due to the contact with the earth? It would be nice to build forms and pour them full with papercrete and save on the cost on delivered concrete; it would be hard to waterproof the earth side of the walls.

A: You're right, papercrete and earth don't mix well. The papercrete gets soft under such conditions and looses its integrity.

Q: I write from Tucson, where I have learned from your site is among papercrete pioneer cities. I live downtown, and am interested in building a sound wall around part of my property. There is an existing chain link fence, and I am curious whether papercrete can be mixed into a paste thick enough to simply layer onto the chain-link plaster style, or if it can be poured directly in place using forms. Advice as to proper foundation for either or both of these possibilities would also be appreciated.

A: Yes, I think that it would be quite feasible to make a papercrete wall over your existing chain link fence. I would suggest some kind of form that would straddle the fence, with the chain link pretty much in the middle of it. I would pour maybe six inches of ordinary concrete first, as a foundation to keep the papercrete off the ground so it won't wick up so much moisture. With the metal fencing imbedded in the wall it should be very strong. I would make the wall at least 6 inches thick.

Q: I do not have any real experience with PC and am hearing stories about PC that traps moisture inside and all of the related horror stories. It would seem that PC can be sealed properly once dry but I do not know how to do this. I recently bought a book "Building with Lime" by Stafford Holmes, an architect from the UK and this book seems quite well researched. It looks like a lime render both inside and out should seal PC but whether or not PC is the right material for New Zealand's damp wet climate, I do not know.

A: In my opinion, you should treat PC like you would strawbales, and keep it out of direct contact of the weather, with good high foundations and large roof eaves. This is if the PC is used to make a solid wall, where the moisture can travel from one side to the other (which it will). I put a lime plaster over the inside layer of PC in my earthbag home, and this has worked out well, and does tend to inhibit the formation of mold. In some ways, I think it is better to allow the PC to remain breathable, rather than try to completely seal it, because once moisture does get in, it can't get back out...just like with strawbales. All of the PC building that I am familiar with has occurred in the Southwest more arid environment, so how it would stand up in New Zealand is a question.

Q: Can one build massive totally underground domes homes with papercrete? Domes 30 ft and larger.

A: I feel pretty strongly that under NO circumstances should papercrete be used for underground construction. Papercrete absorbs moisture like a sponge and it needs to be kept dry to maintain its strength and insulating qualities, and also to keep it free of mold. The best way to keep papercrete dry is to allow it to breathe well; this simply cannot be done underground.

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I specifically disclaim any warranty, either expressed or implied, concerning the information on these pages. Neither I nor any of the advisor/consultants associated with this site will have liability for loss, damage, or injury, resulting from the use of any information found on this, or any other page at this site. Kelly Hart, Hartworks LLC.