How to Make a Papercrete Mixer

There is a lot to love about papercrete as a building material. It’s made out of readily accessible and inexpensive materials: water, used paper and cement. To make papercrete you have to be able to grind up lots and lots of paper. In order to do that you need a mixer capable of shredding paper. A regular cement mixer won’t shred paper it will just stir it around. Luckily for us a guy by the name of Mike McCain invented a papercrete mixer that you tow behind a truck.

Papercrete tow mixer

The plywood top looked good but it didn't work that well

The McCain mixer is sheer genius in its backyard engineering brilliance and simplicity. It consists of a trailer made from a truck rear axle with a stock tank mounted on it. The axle is rotated up 90 degrees so that the end where the drive-shaft would normally attach is sticking up through the bottom of the tank. A lawn mower blade is mounted on the differential stub so that as the trailer is towed it turns the lawnmower blade creating a giant blender.

Inside the papercrete mixer

I built my own McCain mixer a few years ago and it’s worked really well for me. I’m going to go over my build here and post more detailed instructions over at instructables as well (at some point) so that you can build one yourself if you get inspired. (I lost my !@%$&# photos from building my mixer so we’re going freehand from here people!) First I gathered up my materials which included: A four foot diameter metal stock tank A full sheet of 3/4″ plywood Metal beams The rear end from a Land Rover (I think I have the classiest trailer in town) A trailer hitch The rubber inner tube from a large truck tire A couple hinges A lawnmower blade A small can of bondo A tube of silicone and liquid nails Assorted nuts and bolts and some wood screws The first step was to assemble the trailer. I needed a contraption that could securely carry several hundred gallons of water. I used galvanized I-beams that were way heavier duty than I needed to build the trailer with, but hey, they were pretty cheap at the scrap yard and about the length I needed already. I welded them together along with the rear end from a Land Rover to create the framework. Once I welded on a trailer hitch from Pep Boys I had a trailer. Papercrete mixer trailerNext, I cut the plywood sheet in half and glued and screwed the two halves together to make an inch and a half thick platform to hold the stock tank. I cut a hole in it where the end of the differential would stick through. I cut the plywood to fit snugly around the differential so that it would be relatively easy to seal later. After that, I cut a hole in the stock tank as well so that it sat on top of the platform and fit over the  differential too.  Once everything was aligned I drilled through the tank, plywood and trailer rails and bolted everything together. Papercrete trailer plywood platformIn order to get the papercrete out of the mixer I needed a drain.  I took the tank off and cut a hole that was the circumference of the truck inner tube.  I cut a third of the inner tube off and slid it through the hole in the plywood and secured it with a couple screws.   It looks like an elephant’s trunk sticking out of the bottom! I cut a matching hole in the stock tank but made the hole an inch smaller so that I could cut tabs and bend them down to secure the tank over the drain. I bolted everything together and sealed the joint between the differential and the tank with bondo. I also made a flap under the trailer to hold the drain shut.  All that remained was to attach the lawnmower blade to the differential and I had a mixer.

Towing papercrete mixer

Now I use a canvas tarp to keep everything in

How long did it take? I took my time acquiring parts over a few months and then once I got started building it took me the better part of a couple of weekends to construct it. How much did it cost? I scrounged as much as I could.  I did buy the metal for the trailer but it came from the scrap yard so it only cost about $35. The trailer hitch was another $20 and the stock tank was about $175.  Maybe another $20 for bondo, bolts, glue and silicone.  So a total of about $250. What you do different next time? I would re-design the drain so it was easier to use and make it larger to let the mix out better. I also need to put a couple of chains on by the hitch in case something bad ever happens and the trailer comes off. What’s next?Next time we’ll go over actually making a batch of papercrete and casting it into blocks.

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