The Ratio of Materials in Papercrete
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Q: I want some information on papercrete stucco, papercrete blocks: %paper %cement %water.

A: Basically the mix that I use mostly is: 50/50 paper and cement by dry weight, and the amount of water doesn't really matter...just enough to make the slurry. This is for "pure" papercrete, without sand. For a more durable product that doesn't shrink as much and is less likely to burn, add some sand to the mix, and reduce the amount of paper proportionally by wet volume. It is best to experiment and come up with a mix that works for what you are doing.

Q: I used papercrete on an earthbag foundation. The outside skin is 1 bucket concrete, 5 buckets paper trash and very low sand. For the inside I will use 1 bucket concrete and 30 buckets paper trash and 1 bucket sand. Now my question, what will happened, if it rains very strong and maybe rain comes through a crack on the inside mixture, and starts the paper to rot, because the outside skin is to closed to let it go away?

A: OK, my experience is that once the paper/concrete mix has cured, it will not rot, even when saturated with water, as long as it has an opportunity to eventually dry out. But that is with a mix that is probably 1 cement to 4 or 5 paper. The thinner mix that you mention might not resist rotting as well. I might suggest that you use more sand in the mix because it will make it much more fire proof. My final coat is something like: 1 cement, 3 paper, 4 sand (by volume)...this gives a very durable coating that can be troweled smooth if you want.

Q: To use much sand in my test material shows me that the sand has no good contact to the other materials. All the concrete is around the papercuncks. Has the sand no good contact to the other materials in your case too?

A: When I first started mixing sand into the papercrete, I thought that it wouldn't mix very well, so I did two batches (one with just sand and cement, and the other with paper and cement) and then mixed the two batches together. This worked out pretty well, but was a lot of work because I was doing it all by hand. Then when I made the big tow mixer that I pull behind my car, I tried mixing it all in one big batch, and that has worked out well also. The sand does seem to get coated with cement. The paper does have a tendency to filter the cement sometimes, but not enough to weaken the final product.

Q: And my test shows that if I use much paper, it needs a longer time to dry than the test with lower paper. Maybe this is because my material has so many chunks, or is this normal with or without chunks?

A: It takes papercrete a long time to cure no matter how chunky it is; the more paper there is, the longer it will take to dry.

Q: Would there be any advantage to using lava rock with a lot of fines in place of sand in a papercrete mix?

A: I'm not sure there would be any advantage to this, because the papercrete is so insulating in the first place, the addition of lava rock would not necessarily enhance this. I do know somebody who added scoria powder to some papercrete to give the final product a nice pinkish tone, so coloration could be a reason to do this.

Q: I read at the yahoo papercrete forum that papercrete should be only paper to provide a better fire barrier. They/he said the batches with cement/sand smoldered to ashes but papercrete did not support a burn. What is your take on this? In your Q & A you mention to someone to add more sand in the mix for fire proofing. Is this older information that needs updating??????

A: I think you have some erroneous information here. I have not done independent tests myself, but everything I have read anywhere about the combustion of papercrete suggests that pure papercrete (without mineral content and only a modest amount of cement added) will smolder until it is nothing but ashes. The more cement or sand that is added, the less likely it is to burn. In fact tests have shown that when the mineral content approaches 75% of the product (by weight), the papercrete will not support combustion. Another factor is how compressed or dense the papercrete is; the denser it is and the less air is trapped in there, the more fire-proof it will be.

Q: I live in Oregon and would like to construct house walls by pouring papercrete into forms between peeled fir posts, ( maybe 48" x 48" x6" panels, reinforced with two layers of 4" hog wire fencing, between each 8" post). They will sit on a concrete foundation and have a wide roof overhang so that rain should never touch the papercrete. My question is this: Since the papercrete would most likely absorb moisture from our damp air, could I add something like a quart of water-based wood glue to the water before adding the paper, (It should make the paper water-resistant when it dries), or would it be better to coat the exterior with waterproofing, or even paint?

A: Your plan sounds like a good one, in terms of the foundation, posts, wire reinforcement and roof overhangs. I haven't heard of anyone using glue in the papercrete mix to waterproof it, and I have my doubts of this working, because of the basic porousness of the papercrete material. I suggest that you run some experiments to see if this might actually work (and let me know the results.) A more sure way to waterproof the wall after it has dried is the silicone caulk mixed with mineral spirits painted on, and then a possible final coat of Elastomeric paint (this method was used by papercrete pioneer Eric Patterson). Here is another product: Geobond could provide a fast, durable solution to sealing, fireproofing, and scuff-proofing papercrete (www.geobond.net)

C: I have used lime in papercrete. It made a very smooth mix that took a little longer than a cement mix to get hard. Borax in the mix will help combat mold, is supposed to be good for fireproofing and insect repellant too. I used about five pounds of borax per mixer load for my dome. I have not seen any mold but I live in an arid region. I have seen insects die after crawling onto wet papercrete with borax.

Q: Is it possible to use compost as substitute for paper? After all compost used to be paper; and is it possible to make an earthship home filling the tires with papercrete instead of dirt?

A: I think the answer to both of your questions is NO. I'm afraid that compost used instead of paper would promote rotting and mold. The reason the tires in an earthship are filled with dirt is that it can be compacted to create a stable wall...papercrete would not cure well in a tire, would be too compressible, and could lead to problems with mold in the wall.

Comment: I added Calcium Chloride to shreaded paper in the blender. I dried a slug of it in the oven. It dried like a rock!! and it won't burn.

Q: I was looking at creating a mold for making ceiling tiles out of papercrete (2'x2' or 2'x4'). I'm going to try some different thicknesses for sound barrier. My question is about he mixture I would need. I read that latex paint could be used instead of cement to help make a bond. What would you suggest?

A: I know that recycled latex paint has been mixed with cellulose insulation to make a putty that hardens and becomes waterproof. It is possible that such a mix could be used to make ceiling tiles of that size...it would take some experimentation to find out. I suspect that whether you did this or used traditional papercrete to make such tiles, you would need to embed some form of reinforcement (such as chicken wire) in them, or the tendency would be to break apart over time. I would try using a mix for papercrete that would be pretty light, such as 50/50 (by dry weight) of Portland cement and paper pulp. This product would be more insulating than the latex paste.

Q: There seems to be some discussion on various sites that many of the original builders of papercrete are moving away from using cement in their mixtures to a paper/soil block. Can you say if this trend is continuing? If so why?

A: People are always experimenting with papercrete mixes and uses. The use of cement has a negative environmental impact, and of course it is more expensive than the soil at your doorstep. Also, purists want to be as natural as possible. The use of cement will stabilize papercrete over time, whereas the soil can dissolve in water. For this reason I would recommend the soil-paper combo to be used exclusively indoors, or at least in well protected areas.

Q: I have read a lot about papercrete and come up with the following idea:- since paper is a wood product, what if I use fine sawdust for the same application as it is simple to process and widely available in my locality.? I am from equatorial East Africa.

A: I have heard of sawdust being used this way in the past, but I am not sure how successfully. I suspect that there are several variables that would be a factor in how well it would work: the specific type of wood used, how fine the sawdust is, what ratio of cement is used, and whether any other mineral material is added. I would suggest experimenting with all of these factors to see what seems to work best.

Q: I want to know the relative material in volume units not in per cent as you show in your web site, for example: 6 volume of paper, 3 of sand and 1 of portland cement.

A: The formula for papercrete is rather flexible, not exact, but I would say that in dry volumes it might be 3 paper, 0-3 sand, and 1 cement. However, once the paper is wet and pulped, this would expand to maybe 10 paper, 0-3 sand, and 1 cement.

Q: One person mentioned adding wintergreen to pc mix to keep it from spoiling ? Does pc mix spoil ?

A: I have never tried the wintergreen, so I can't say much about it. The only pc that I know to spoil is slurry that is left standing too long (over a week), especially if no cement has been added to it. This can begin to smell pretty foul.

Q: Another person suggests adding borax to pc for fireproofing and mold retardant.

A: This might work, although I have not tried it. Borax is added to some forms of insulation (wool and cellulose) for this same purpose.

Q: I have a client who wants a home that papercrete might work with. I am interested in the various formulas.Do you have any suggestions?

A: The more mineral material and Portland cement that is added to the paper pulp, the denser and more fire-resistant it will be, but also this diminishes the insulating value somewhat. I did some calculations based on the size of my tow-mixer and realized that it holds about 0.6 cu. yards of slurry when full. Into this hopper I put 1 sack (94 lbs) of Portland cement, 1 wheelbarrow full of sand (unless I need a "light" mix) and the equivalence of a stack of folded newspapers some 12" high and weighing about 40 lbs. (dry). Without the sand, the amount of paper would be increased to 60 lbs or so(dry). The slurry that results from this, once the excess water is drained from it to make a putty that can be applied by hand as a plaster, produces only about 0.4 yards, I would say.

Q: I am mixing all kinds of different constituents for testing in my back yard. I even picked up a bag of lime. Trouble is I know absolutely zero about lime. I want to test blocks made with it. Do you have any idea of how I would proceed? That is, how much lime to use in a given amount of papercrete to make a block? The lime is powdered. I need to make two cubic feet of mix for two test blocks - 12" x 24" x 6". Two cubic feet is about 15 gallons of paper pulp. So, any idea of how much lime to put in? Also, do I just throw the powder in the mixer with the pulp or put the powder in first? I don't want it blow up on me. I will wear gloves, safety glasses, overalls, etc. Any insights you can provide would be very helpful.

A: I have never tried using just lime, but I have often thrown in some with the Portland cement, and I once had quite a few free bags of mortar mix, that has lime in it also. I presume that the lime you have is "hydrated", which means that it has already gone through the process of water being added (or slaked), and then this was dried again for reuse. This stuff is much safer to work with than the other kind that will actually bubble and boil when water is added. If you are intending to use just the lime to get the PC to congeal, I think you going to be in for a long wait; just the straight lime (lime putty) takes a long time (maybe a couple of weeks) to thoroughly cure, and if it is added to the wet paper pulp, it will take much longer, maybe months, to harden...I am guessing. It does not "set up" like cement. As for how much lime to throw in, I would suggest at least as much as you would of Portland cement, say a full shovel-full for 15 gallons of pulp, and maybe much more. I would put it into the already mixed pulp. Like I say, I have never tried this. How it will behave after it eventually cures, is also a question...whether it will hold up to abrasion or moisture? If this works though, it could be an environmentally more benign PC, in that the lime actually absorbs CO2 as it cures.

Q: Do you have any information regarding papercrete density?

A: The density of papercrete really depends on how much cement and other mineral material is added to the mix. With not much cement and no added earthen material, papercrete is quite light and not very dense,  perhaps with a density of around 25 lbs/CF. Otherwise, with the addition of lots of mineral material it could approach the density of lightweight concrete.

Q: Do you know the pounds per square foot (PSF) of a one-inch layer of papercrete? And a one-inch layer of cellulose spray without the concrete? I'm planning on putting papercrete on the outside of a 22 gauge quonset-style metal building and cellulose spray insulation on the inside.

A: I don't know exactly the PSF figure for 1" of papercrete, but I would guess somewhere between 1 and 2...which would likely be more than the cellulose without the cement. The value for papercrete would vary depending on the formula used and the addition of any mineral material.

Q: Have you heard of any experiments involving papercrete and used motor oil? I had this crazy idea that if oil is added to the mix it may help make the papercrete water resistant. I am concerned that it may affect the bonding properties of the cement though. Any thoughts?

A: Yes, I think that this is a rather crazy idea; I would be very surprised if it works. Oil floats on water, so it will just float on the slurry until all of the water is absorbed or drained out of the pulp/cement, then it will coat the surface of the papercrete at that point. You could try to mix it into the moist papercrete, but I doubt that it will do much more than weaken the bonding of the material. If you try any experiments with this, let me know it works out.

Q: Water-cement ratio has something to do with the strength of concrete. Isn't it true for papercrete also?

A: Interestingly, the ratio of cement and water has no affect on the ultimate strength of papercrete. Basically, all of the cement becomes bound with the paper fiber which filters it out of the water, so the effluent is nearly crystal clear. The ratio of cement to paper fiber is what determines the strength of the product.

Q: I've been using a formula for papercrete that uses pumice in place of sand. My slurry is easier to mix (because the pumice doesn't sink to the bottom of the mixer), the blocks are lighter and have a higher profile. I'm happy with the blocks but would like to be more environmentally responsible by using fly ash in the mix. I've read they are capturing fly ash at the power plant in Bloomfield and saw a container labeled fly ash at the Lafarge plant in Santa Fe but haven't been able to find a source for a small user like myself. Lafarge doesn't sell it. Do you know where I can get some? Is there a commercial mix (like Quickcrete) that includes fly ash? I'm in Abiquiu, NM about 50 miles north of Santa Fe.

A: That is interesting about the pumice mix. I know somebody else who experimented some with something similar, adding scoria fines to his papercrete, and it turned the product pink, but it was sound. I wondered about experimenting with fly ash as well, but was never able to locate a supplier in small quantities. I'll forward your query to our adobe specialist who happens to live near you; perhaps he will have some idea about where to get fly ash in your area.

A: (Quentin Wilson) APS (Arizona Power Something) views the flyash as a"product" and not waste material. Therefore, they are looking for ways to market it. My understanding is that the product goes out in large bulk hauling semi trucks. Much of it is used as an admixture in the concrete industry where it makes concrete easier to pour and level while apparently reducing the amount of Portland cement required. We had hoped to get enough to fool with here at the College but it never worked out even with our slight "insider" advantage. It requires care in handling since it is in a finely powdered form. Anything finely powdered can be a problem for human lungs. I am thinking that they simply do not have a system for filling small containers in a safe manner at the power plant.

A: (Bruce Salisbury) Fly ash is a Manufactured material. As long as I include an MSDS for it. It can be shipped. It is not classified as Hazardous, so I can ship it via UPS. I frequently ship it in 5 gallon containers.

Q: Would adding alkaline pesticide to the mixture be a good way to avoid papercrete's susceptibility to termites?

A: My experience with papercrete is that it is not susceptible to termites...they don't seem to be attracted to the fiber once it is coated with cement.

Q: Would the following mixture of papercrete be able to pour in molds, or does it contain excess of water making forming it difficult? 160 gallons of water
60 pounds of paper
94 pounds of portland cement
65 pounds of sand

A: Virtually all papercrete requires excess water to make the slurry, and this excess water must be allowed to drain away, either in the molding process or just prior to it. The excess water can be recaptured for future batches if desired. The formula that you list looks like it would probably work,  if you have a big enough mixer to handle it.

Q: Would it be possible to use the bagged cellulose insulation sold at Home Depot?

A: I see no reason why bagged cellulose couldn't be used to make papercrete, but given that you can find lots of free surplus paper in most localities, why would you want to?

C: (Kathryn) I just got my first set of results back from a soils engineering laboratory on a paper amended mud line of products I'm developing, and the compression strength of the standard sized adobe block is a whopping 2,300psi. A regular asphalt emulsified block comes in at 300 psi. The block actually exceeded the capacity of the compression machine with 300,000 pounds applied on it without rupturing. Amazing! I've put some lime putty into the block mix as well to build in the water resistant qualities, rather than depend on plaster applied afterwards. Blocks left outside over the monsoon season of summer have edges on them as sharp as the day they were formed. This strength was demonstrated with half mud made of 30% clay, and half paper. The next generation of mix to be tested will be 25% mud with 75% paper that we get to keep out of the landfill. We seem to have some room to play in complying with the 300psi standard coming down from 2300psi!!! 

Since we have no vehicular access to the building sites, the paper mud product is being developed for a lightweight high performance building material option. We'll be using it not only for furnishings such as countertops, benches and tables, walls, domes and vaults, but also for interior and exterior floors and for roof systems. I'll be trying to keep information current on my blog http://www.domes. blogspot. com .