Papercrete as Plaster

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: Seems like papercrete would be a good plastering material for the straw bale house I am building. It breathes well which is important for the bales. Do you think it would adhere well to the bales?

A: I know of several situations where papercrete has been used as a plaster over straw bales, and it has worked out well. The papercrete should adhere to the bales just fine, especially if it is the straw ends that are exposed and being plastered.

Q: Perhaps it should be sealed somewhat so moisture does not reach the bales? If so, maybe use a limewash which I understand still breathes?

A: This might be a good combination. I used a lime plaster over papercrete on the inside of my house, and it adheres pretty well, especially if the papercrete is textured roughly. I suggest some controlled experiments to see what works.

Q: Chrysalis Living Center here in Tucson builds houses which are "stuccoed" with papercrete. It is shot on under pressure from a hose just like conventional stucco. In this case, it is covering polystyrene sheets lathed with stucco netting. I am wondering why I couldn't just shoot the papercrete onto the strawbale walls in this way?? Do you think it would adhere well doing it this way?

A: I'm pretty sure the papercrete would adhere just fine to a rough straw bale, especially if the bales are oriented with the straw ends sticking out. Spraying the papercrete would probably be a very effective way to do it, if you have access to the equipment to do this.

C: I sure wouldn't want to have to put stucco netting on my bales though (groan). I was already thinking of making a water storage tank/pond by shooting papercrete on the sides of a huge hole which has been dug on my property (to get enough earth to build up the floor between my (way too big) stem wall ordered by the county for the strawbale house.) I would then line it with visquene I guess. Point is I would have the machine already on hand to use for perhaps shooting the straw bale.

A: You would definitely need to line the tank with plastic, or somehow waterproof it, or the papercrete would wick the water to the other side.

Q: I am wondering if the lime could be used right in with the papercrete mix -- much as they do with a lime stabilization for earthen plaster? Has anyone ever done this?

A: I recently read a book by Charmaine Taylor called "All About Papercrete", where she describes lots of experiments with different formulas, including the use of lime. As I recall this can work, especially if there is also some clay in there to help harden the lime. The curing time can be very long, and the resultant product is not likely to be as durable as papercrete with Portland cement, especially in situations where it might get wet.

Q: What machinery do you use to spray the papercrete?

A: I did not use a sprayer on my house. All of the papercrete was applied by hand. I did try an experiment with a sprayer once and it was a partial successful, but it required a huge compressor and was difficult to control. I do know that papercrete has been successfully sprayed using a diaphragm pump with considerable air pressure. The paper fiber has a tendency to clog nozzles and small diaphragms.

C: I read about using paper, water, and cement as a plaster. I don't know how it will withstand our termites so I will have to give it a try.

R: As you may know, we used "papercrete" to plaster both sides of our earthbag domes, and it has worked out very well. This material does seem to resist termites and other insects.

C: As it is working against gravity, I am stumped as to what to use and how to keep it from falling off.

R: We had the same situation with our domes, and I used polypropylene baling twine wrapped around the earthbags as I built the structure (circling 3 bags at a time) to give the interior plaster something positive to grab onto. Also I used a very light mix of pure papercrete (no sand added) on the initial coat. This I threw up on the wall by hand and let it splat and dry in place with a very rough texture. It is amazing that the stuff would actually adhere to horizontal surfaces and dry in place. Once it has dried, more can be added to fill in all of the voids and make as smooth a wall as desired.

C: You discovered that throwing the crete helped it stick better than troweling. This has been done with pure lime plasters for hundreds of years and is called "Harling"..there is even a type of exterior lime plaster called Lime Harling...a thin flexible tipped wide trowel is used to scoop the plaster, then flung with force against the surface, it is lightly trowelled then and left to cure. The Scots are clever folk and found they could be more successful with plasters in a harsh climate if they flung it ( hence the Scottish fling- but that's another story) there is an engineering principle behind this, ( don't ask me to explain it) and I have also written about it when building my cob-crete garden bench. I harled the cob/crete plaster or threw it by the handful. and it is a wonderful tension releaser...! (Charmaine Taylor)

Q: And do you know at which point there is no breathing in a papercrete wall? Or is every papercrete wall breathing well?

A: I believe that any papercrete wall will breath, as long as it is not painted or coated in some way to prevent that.

Q: Will papercrete adhere to expanded polystyrene? I know the synthetic stuccos like Dryvit will stick to foam board. It would be really nice if it will stick to the foam board???

A: I've never tried what you suggest, using papercrete to cover foam board, but I have my doubts that it would stick. Papercrete does best as a stucco when it has a fairly rough surface to adhere to, otherwise it just doesn't tend to stick that well.

Q: How is the external papercrete on your house holding up?

A: I'm quite pleased with how the papercrete is holding up so far. One building is already about five years old and is showing no sign of deterioration. There are a few small cracks in the papercrete plaster in some places, especially on the south side that experiences more thermal stress. However, since I imbedded chicken wire in the final coat, and since the entire earthbag structure is not vulnerable to moisture damage, these cracks do not concern me. I will eventually caulk them to keep the material from flaking off.

Q: I am interested in using papercrete as the stucco/wall material in a Tudor style cottage home in New Hampshire where there is a lot of snow! The material would not be used in a load bearing application. The material would be exposed to a lot of weather. I am looking to make it waterproof and fireproof. Is the GeoCement product a way to go in lieu of regular portland cement as it is waterproof and fireproof? Any idea if it is financially realistic?

A: The main thing to realize with papercrete is how much is likes to absorb moisture when it has a chance. It is like a sponge. So it is best used in situations where, even if it gets wet, it won't cause any harm. If it is allowed to breath it will evaporate any moisture quite readily, but if it is sealed and still gets wet, then it will stay wet and could cause problems. I have not actually tried the Geo Cement product, so I don't have direct experience with how well it works or how cost effective it might be. It does seem like a reasonable approach to waterproofing and fire proofing papercrete, when necessary.

Q: I recently purchased land and am living in a single-wide trailer until I can build. Any ideas on a cheap fix for poor insulation? Could I papercrete the outside walls?

A: A fast, but temporary, approach to insulating a trailer is to line the exterior walls with straw bales where possible. This could last a few years. Papercreting the exterior could be another solution, but it would take a lot longer, and the whole question of dealing with moisture might be an issue. Papercrete holds water like a sponge.

C: I bought a new manufactured home in 1992. I was having problems with plaster sticking to pillars that were not plastered right. I took the papercrete idea and used it. I soaked newspaper in hot water, then ran them through a blender, and added the cement. I used this instead of the plaster and it worked great for the repairs. No more problems. Since then, I have used a regular paper mache mixture of paper, flour and water to add a textured plaster finish over a very ugly wall. (P.S. Don't forget to add a little wintergreen to keep the mix from spoiling before it dries!) After this dried, I painted it and have a great looking wall with very little money involved.

Q: Could cob and papercrete be combined?

A: I did an experiment at the last Natural Building Colloquium of applying a papercrete plaster over an existing cob wall, and it seemed to adhere quite nicely, although I have not returned since to see how well it is doing.

Q: I have to make a small walls inside the house to divide the bed rooms and the living room. I want to use papercrete to joint the bricks and finally as a plaster. What do you think about this? Is it possible or not?

A: This seems like a good idea to me...I don't see why it wouldn't work. You can trowel the papercrete as smooth as you want. Many of my interior walls were done this way, and then stained with a wash of latex paint mixed with a lot of water.

Q: I was wondering about using a papercrete first coat and then a finish coat of ferro cement on my home. I live in Arizona where it rains only in the monsoon season and I live in a questionable flood zone so my house is two feet above the surrounding ground.

A: I think that idea is a good one; the initial coat of papercrete would provide insulation, while the final coat of ferro-cement would provide durability and fire protection.

Q: Is
using cement in covering papercrete buildings a good isolation material to increase the poor moisture resistance of the papercrete blocks or not?

A: A plaster of cement (stucco) would definitely increase the resistance to moisture entering, especially if it has a high ratio of cement to sand.

C: I was raised with an Uncle who was a stone mason/landscape architect in California. I still love mixing mud or cement (now papercrete and earth plasters by hand). I want to share with you two of my latest finds. One using a pudding thick wheat paste mixed with very fine nature colored sand or clay to make an earth plaster faux brick archway that folks can't believe ain't real.

Second is using the new 85% recycled paper blow in insulation in my paper crete mix, allowing for less water and special mixing. I use 1 part portland cement, 1 part fine sand and/or clay, 1 part blow in insulation and I use a portion of masonry white glue in the mix too. I am using that as an indoor outdoor earth plaster and hope to pour my faux adobe courtyard walls using that mix as well.

Q: I am starting an earthbag construction, and just wanted to ask you how the papercrete stucco has held up over the years? Any problems with cracking like in typical stucco?

A: I have noticed over the years that some of the papercrete that is exposed to lots of wear, like on top of the vaulted entrance and at the base of the windows where the water is always sliding off, has eroded some. There were some cracks in various places as well, which I sealed up with caulk. We sold that house and I have advised the new owners that they might consider applying a standard finish coat of stucco over the whole building to protect it better in the future.

Q: We would love to use papercrete for the inside plaster, can it be painted?  My wife is a real Faux finish person and wants to do some strange things.   Or maybe you can just mix pigments in the papercrete mixture, rather like fresco.

A: I used an interior papercrete plaster in the earthbag home I built in Colorado. Since I wanted to keep the walls as breathable as possible I did not paint them. Instead I stained them with a watered down latex paint after they were cured, and this worked out quite well. In fact it gave a finish that resembles some faux finishes.

Q: Can a drywall or texture type hopper gun be used to spray papercrete? I want to cover an old mobile home with some type of papercrete mixture--perhaps with latex paint or asphalt emulsion added for sticking over the metal siding. I originally thought of applying the mix by hand, but would rather spray it if I can find an affordable means.

A: Papercrete has a tendency to gum up sprayers because of all the fiber. The only sprayer that I have seen work very well is one similar to one manufactured by Tirolessa.

Q: I have been using the Walkmaker form to make faux papercrete stones for siding, to be applied over OSB. I was going to apply chicken wire prior to applying the stones and had even thought of sealing the OSB with a good exterior paint prior to adhering the stones. My question is, do I have to apply tar paper over the OSB before adhering the stones with a masonry cement mixture over the chicken wire?

A: The common practice with cement stucco over wood sheathing is to use tar paper between them, and so I think this is also a good idea with what you are proposing, especially since the papercrete stones will hold more moisture than ordinary stucco.

Q: Could you share your experience with how the papercrete plaster you used over the earthbag house that you built from 1997 to 2000 has faired over the last decade?

A: I would be happy to post an update about that earthbag/papercrete home. We lived in it for about 6 years before selling it to live in Mexico for the next five years. Overall, the structure is as sound as the day I finished it.
I'm sure there were also a few cracks in the PC plaster that developed over time, but I never worried much about them because of the nature of the wall system employed.

As you know, the papercrete was used as a plaster over the earthbags, both inside and out. After about a decade of exposure to the elements, the exterior PC plaster was showing signs of erosion in certain places, most notably at the base of the embedded glass where moisture would accumulate and on the more horizontal aspects, such as over the door eyebrows and the top of the vaulted entry way.

The folks who bought the house were concerned about this, and so was I since I expect that house to last for centuries. We discussed how to protect the plaster generally, and at my suggestion they went to considerable expense to have a professional stucco crew do a stucco job over the entire house, complete with more wire mesh embedded in it.

Papercrete makes an excellent substrate for almost any further plaster work, since it is so amazingly dimensionally stable under most any condition. The lime plaster I troweled over the interior PC has held up very well, and I expect the exterior stucco to do the same. This does mean that the structure is not quite a breathable as it was with just the PC plaster, but I think it is sufficiently breathable, especially since it can still breath quite well inside.

I was always amazed at how well the combination of earthbags filled with scoria and plastered with PC performed as a skin for the house. At least in this rather arid environment there was never a drop of moisture that came through that package. I think that the PC acted like a sponge and just held the moisture at that level, allowing it to soon evaporate rather quickly. It was never damp long enough to develop any tendency to support mold.

Q: I was hoping to spray papercrete onto the internal walls of a reefer container (food grade stainless steel) If I sprayed fine coats and address some glue do you think it would take or over time just fall off?

A: I see a couple of challenges with this idea. One is getting the PC to cure in that environment, but if it were thin enough and you provided good ventilation for several days, it might. The other is getting it to stick. I think you would have to line the wall with wire or synthetic mesh that is attached to the metal to make it stay put.

Q: My father built a 12'x24' "barn" approximately 40+ years ago and I would like to apply papercrete or a similar stucco-like surface to the exterior. It is built from sheet plywood that is showing it's age to say the least. I thought a stucco like surface would insulate the barn as well as hide the imperfections and holes that have happened from age and weather. The small barn has a dirt floor and a tar paper roof. It's very modest. I just want to now reclaim it. I also thought applying this type of surface would be a simple and more durable one. What do I need in terms of equipment and supplies? Cost is an important factor. Is this the inexpensive and practical "fix" I really want and can do by myself? We live in Northeast Ohio and winter can be severe. Spring thaw also creates a very muddy field and barn floor....

A: I think that papercrete would probably not be your best option for this. While it is insulating, it takes quite a bit of it to make much of a difference. This fact, coupled with the difficulty of acquiring equipment to make it and that it doesn't necessarily hold up to weather over time, makes it less than ideal as a plaster.

Q: I have been seriously considering covering the outside of my adobe home in a layer of papercrete, but can't find any info on this subject. I read that you had applied papercrete plaster to the outside of an earthbag wall; is it holding well? Does the concrete in the mix lessen the breathability of the wall any? Can you cover papercrete with earthen plaster?

A: Papercrete would serve as good insulation for adobe, as long as the eaves of the house are large enough to keep most of the moisture off of it. I did use papercrete over an earthbag dome house I built once, and it held up pretty well for about a decade, but then started to erode. On a vertical wall this might not be a problem. Papercrete is naturally quite breathable. Yes, you should be able to use an earthen plaster over papercrete, as it is an excellent substrate for plasters, neither shrinking nor expanding with changes in humidity.

A: I'm trying to plaster the interior of a trailer with papercrete, especially for insulation. I'd like to keep as light a mix as possible. The papercrete doesn't seem to stick very well to paint or paneling... is there anything I can or should add to the mix to boost adhesion?

A: You can't really expect much adhesion from papercrete; it needs some plaster mesh of some sort, like chicken wire or fish net attached to the wall, for it to stay there.

Q: Is it possible to use papercrete plaster on a new Sheetrock wall? Concerned about it sticking to the wall.

A: You're right that the papercrete wouldn't stick to the sheetrock. You would need to provide some sort of lath to support it. Furthermore, the moisture from the papercrete would not be good for the sheetrock.

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