Our House

I’ve been perusing the net reading up on papercrete; what people have done and what they think. I ran across a bit from someone who asked why anyone would want to pour a whole wall at once. They stated it would be heavy but it could probably be done with sufficient rebar to keep the wall structural intact while being lifted into place. Rebar? Okay, I can see where that could be a good thing if you didn’t already have a support scheme in mind for the wall or you expected the papercrete portion of the wall to be structural.

As to the weight, 60 pounds of paper, 65 pounds of sand, 94 pounds of concrete and 1334 pounds of water makes a pretty hefty wall (1500+ pounds). But a bunch of that water is going to drain away when the slurry is poured into the mold, then a bunch more is going to evaporate as the wall cures and dries. So say you’re left with 10% (actual dried wall content should be closer to 2% – 27 pounds) of the water still in the wall. That’s only 150 pounds! That would give you a total papercrete wall weight of 369 pounds per mixer load of water. So if a wall takes two mixer loads, you’d have a finished papercrete wall weight (12′x8′x6″) of around 700 pounds. Not too shabby! I’m asking Nolan what he thinks a ferrocement wall would weigh.

I’ve seen mention of people making papercrete logs (actually, really long bricks) that break in two when lifted, so I can see tensile strength is an issue. Being able to use the layup table to tilt the wall to an upright and pickable (a lift is called a “pick”) position is going to save me from adding structural steel to the papercrete layer. I may cheat and add one layer of chicken wire between the two batches of slurry as insurance, though having the papercrete layer tied to the ferrocement layer should be all the stabilization the wall would ever need.

Nolan says a square foot of cement weighs 130 pounds. If I assume my ferrocement layer is going to be 1″ thick, that gives me a square foot weight of 10.33 pounds. That puts the ferrocement layer for my sandwich wall at approximately 800 pounds. I’ll bump that to 850 pounds to give myself some wiggle room. I’m not calculating the full 12′ x 8′ because I have to have the reinforcing exposed around the edges for connecting to foundation, bond beam and reinforcing of the adjacent walls. Leaving 6″ exposed all the way around may be too much, but for testing I’d rather have too much exposed than not enough to work with. I can add concrete, I can’t necessarily take it away.

I did a little gross calculating and have determined it will take two mixer loads to build each papercrete wall panel. The mix of choice is:

160 gallons of water
60 lbs paper (newsprint)
65 lbs sand
94 lbs (1 bag) portland cement

Two batches should give me a panel that’s a little over 6″ thick. I will have to find something to do with any leftover mix. I will also have to figure out how to make sure all the panels are the same thickness. The panels all have different window and door configurations, so this could get interesting.

Because I am using only 16 bags of portland cement for the papercrete (2 per wall), I may want to use white portland for the first layer of each wall (the portion of the wall that is inside the building) and regular portland for the subsequent mix layer. That would give me lighter brighter walls inside allowing me to use a latex wash on the walls instead of actually applying layers of paint. The inside colors would then be brighter and clearer without the gray cast of the portland cement.

Using papercrete does cause a problem. Because I need an expansion layer between the papercrete and the ferrocement layer, and because I can’t cover the papercrete until it’s dry, push through connectors aren’t going to work. I can’t lay the EPS over the wet papercrete or drying will be inhibited.

In searching the net for nylon screws I hit on a neat thing! Threaded nylon rod, a 12″ length for $1.50! With 1″ EPS, I can take a 12″ rod, cut it into 3 pieces and push the nylon into the wet papercrete so it protrudes enough to go through the EPS and lock into the ferrocement layer. Poof, instant push through connectors. I can even spin nuts onto the end if I think I need a little more grip, around the outside edges or on the corners, for example. 16″ centers is probably too close for my app. 16″ on center is structural, and I don’t need structural. I just need everything to be held together until I can get the walls up and fastened together. 30 connectors per wall should be adequate. That’s 10 nylon rods, $15 per wall for connectors. Wow! I bet I can’t get any fancy connector for anything close to that price.

Now I just need to figure out how to keep the connectors upright and in place as the papercrete dries. I’d like to be able to put a *weight* on the form to add some compression while it’s drying. Not anything heavy, just something to help with the initial leveling to give me a more uniform layer. I’ll have to think on this some more.