Making construction materials out of shredded paper

Here’s my deal: I have a paper shredder. Back when I lived in an apartment complex where someone just came around to fetch the trash, I threw the stuff out and I was okay with that. Now that I’m out in the country, I have to pay for this service and I’m limited by volume. Shredded paper is bulky. So I want to do something else with it.

I bet I can turn this into a construction material. It’s probably one of the cheaper materials I can make, I think. The base material — the thing that makes up the bulk of it — is free.

The Paper

The paper I’m using is shredded junk mail, mostly. I don’t separate it much. The envelopes have the plastic see-through windows on them for the address; that gets shredded along with everything else. Sometimes I shred old CDs (because why would you keep CDs?) or credit cards. Pretty much whatever comes in the mail or whatever I don’t want to just throw out because it’s got sensitive information on it.

I’ve got a very standard cross-cut shredder. I think I got it online for a couple hundred bucks. It works fairly well. I have the shredded lubricating sheets which I use once in a while and I usually bag the shreds. I used to not bag them and it was an awful mess.

The Concept

I’d like to make bags full of compressed paper shreds. I’m really flexible on the result, it doesn’t have to meet very stringent requirements. I don’t want to add too much to it and I want to use standard bags. The shredder bags are fine. Regular plastic shopping bags would work too.

I don’t need a permanent material. I’m not actually building a load-bearing structure. My first need is as a liner for a graywater system. If it works well, I may use it as-is or modify it to do bigger and better things. Mostly, I want to see what the properties of it are.

The Research

My first hit came up with this thing about papercrete. It sounds a little rude but the concept looks like it’s exactly what it up my alley. They’re making blocks that I’m imagining are going to be similar to cinderblocks. They use them for actual construction and there’s no plastic bag liner. They do say that they absorb a lot of water so maybe if I modify the plan to work with a plastic liner it’ll be more water resistant.

Papercrete

The people making this stuff seem like a bunch of people just like me. They have space, tools, access to stuff, etc. and they’re looking to re-use their clean, dry trash for construction materials.

They’ve got a process and it seems like most of their stuff is based on that. I couldn’t find any recipes so I’m going to have to adapt their method to use what I have.

The core of their process is some fancy custom-built shredder thing. It’s quite clever: it’s a trailer that you run behind a truck and it uses the motion from the turning wheels to shred paper and mix it with concrete. I’ve got a cement mixer though, and my paper is already shredded. If I can adapt the process, I think I can make it work.

So he’s got a stock tank of some unspecified volume that’s 4 feet in diameter. For this setup, his proportions are a 3/4 full tank of water, 75 lbs of material and a 94-lb bag of portland cement. I’m going to have to re-scale this and I’m going to have to weigh some of my paper.

As for the tank, I found a similar-looking one on Tractor Supply’s website. It looks to be about 75% as tall and it’s half the diameter, but it’s measured at 23 gallons. Doing some math, I’m estimating that his tank is about 29.6 gallons. Let’s call it 30 gallons. So that’s about 7.5 gallons of water or, by weight, about 1.25 lbs of water for every lb of paper. Similarly with the cement, it’s about 1.6 lbs of cement per lb of water, or 2 lbs of cement per lb of paper. So paper-to-water-to-cement, by weight, should be about 4:5:8.

Modifying the directions and stuff a whole bunch, here’s what my first run is going to be:

  • 30 lbs of paper, pre-shredded by my shredder.
  • 1 60-lb bag of regular Home Depot high-strength Quickrete.
  • a 5-gallon bucket of water, mostly full.

Depending on how much volume 30 lbs of shredded paper takes up, this may or may not fit in my (3-1/2 cubic foot) cement mixer. The actual amount of water was 4.69 gallons, but that rounds well within 5 gallons — a contractor bucket — given the estimation error on this whole thing. Plus, the person who posted the papercrete block article seemed imprecise with the water and I live in a fairly dry climate. I figure that at worst, it’ll take a little time for this to dry. I’m also substituting the cheaper concrete mix for portland cement. I had a roommate in college who was a civil engineer and went to concrete lab all the time. He could probably tell me the difference between concrete and portland cement, or I could look it up. I don’t know if it matters though. 30 lbs is 3.75 gallons of water. I know without even picking it up (again) that a full shredder bag doesn’t weigh that much. I’m probably going to need 2 bags full.

More to come as I get to trying!

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