Experiments in Papercrete: Part 1

With our recent move to a 6-acre property, our long-term efforts in transforming a former horse ranch into a hobby farm have been challenging. For me, this has been nothing short of fun. My wife and I have plunged into this new realm of self-reliance with passion, excitement, and curiosity. We have a lot of work cut out for us over the next year or two.

One of our primary challenges is sourcing free/cheap building materials. I must admit that I have become a Craigslist junkie as of late, and the opportunities there are limitless. All you need is a little imagination, a little technical know-how, and a lot of ingenuity. I am particularly fascinated with recycled materials, such as scrap wood, wood pallets, straw, cardboard, manure, and various other items that usually appear — on a frequent basis — under the “free” section.

What can I make with all these free materials? Papercrete!

What is papercrete (I hear you asking)? Papercrete is simply the use of re-pulped paper (mush) in a cement or clay mixture. When dried, the resulting product is a lightweight, insulative building block or brick. This is exactly the sort of thing that appeals to me. With the right block design, coupled with the ideal mixture, I can cast these blocks en masse for various uses on the farm. And boy do I have 101 uses for an all-purpose block.

With our planned construction of raised garden beds, a charcoal retort, a root cellar, aquaponic system, etc., imagine the cost of using cinder blocks, traditional bricks, or some other store-bought building material… It would not only be expensive, but it would deviate from what we’re trying to do — learn how to do this ourselves, and do it sustainably. Papercrete, adobe, or some variation of either would fit the bill nicely. In fact, I intend on combining the best attributes of both — along with my own criteria — to produce my own hybrid block.

My Criteria for the perfect building block:

• Inexpensive to produce
• Lightweight
• Portable (when not used with mortar)
• Sustainable

Here are the ingredients I will be testing:

• Cardboard
  • Price: Free (not including the cost of gas to pick it up)
  • Method: shredded, soaked, and blended in water in 55-gallon plastic drums
  • Advantages: Serves as a fibrous, light-weight, insulating material
• Straw
  • Price: Free (not including the cost of gas to pick it up)
  • Method: Unbound and mixed with the slurry
  • Advantages: Excellent reinforcement for block or brick
• Clay
  • Price: Free (if sourced and sifted from the earth on our property)
  • Method: Sifted and mixed in with slurry
  • Advantages: High plasticity
• Portland Cement
  • Price: Inexpensive
  • Method: Mixed with the slurry
  • Advantages: Provides the cement for the block

I have already tested variations of this formula. Although I have not tested straw — or the straw that exists in manure — I had excellent results. I also experimented with perlite and vermiculite as a light-weight aggregate. These worked well, but their high-cost would defeat the purpose of my quest. After some extensive research, I believe straw would bring similar light-weight attributes to the recipe. Additionally, unlike perlite and vermiculite, straw will serve as a reinforcing fiber to the final composite.

You can see the various mixtures on my initial papercrete trials. The darker grey coloring is from a cement-based, waterproof coating. It was added two days after my initial casting and is ready for submersion testing.

The results from my initial tests produced very lightweight bricks. They lacked the compressive strength that you might find with traditional concrete (sand, clay, and cement), but they were far less brittle. In fact, I took a few hard swings with a hammer on all my blocks, which resulted in little more than an indentation (third block from the right). Since I do not intend on building any load-bearing structures, I think this papercrete journey will lead to a great solution.

I will be posting more photos of my experiments in later posts. For now, papercrete looks like a winner.