Papercreters: [papercreters] Re: Earthbag, Superadobe, Hiperdobe, why not Hiperpapercrete?

Tuesday, March 13, 2012

[papercreters] Re: Earthbag, Superadobe, Hiperdobe, why not Hiperpapercrete?

You post a common, but excellent question, Vickey.

I know it seems counterintuitive, but it is true that papercrete increases in insulation capacity when the damp slurry is compressed.

Pardon me for putting on my scientific nerd hat, but I want to help you understand exactly what is going on and why.

You are correct that it is air pockets that are key to insulation slowing the transfer of heat.

The key is to understand that papercrete is NOT fiberglass.

Fiberglass, as the name suggests, is made from lots of very thin strands of hairlike glass fibers. Each fiber is a tiny solid rod of glass. The way fiberglass becomes an insulator is to create air pockets around the glass fibers. It's those air pockets that are the insulation, not the glass. The glass is simply a loose, very permeable structure that simply slows down air movement. The fibers slow down convection currents inside wall cavities so that the air inside the wall insulates better.

Fiberglass does not perform well if it is packed down. That squishes out all the air, and the air is the insulator. Fiberglass must remain fluffy to fill the cavity it is placed into. Fiberglass also needs plastic vapor barriers and semi-permeable air infiltration barriers that are installed correctly and sealed to prevent air currents from blowing right through the fiberglass and rendering it ineffective.

Papercrete is a completely different material. It is a cementitious cellulose composite. Cellulose comes from trees. It is what paper is made from. It's a form of wood. As the name cellulose implies, it is made up of plant cells. Each cell is a microscopic but extremely durable bubble that does not easily pop like soap bubble. Think microscopic ping pong balls.

When papercrete is compressed, you squeeze the bubbles closer together. While this eliminates air gaps between bubbles, there is still air trapped inside those bubble cells.

Compressing damp papercrete makes it far more difficult for air to pass through the cured dry papercrete, but there are still bubbles of air trapped inside.

I have posted previously about my experiments using a homemade calorimeter to test various insulations. In every case, compressing papercrete increased it's ability to resist the transfer of heat. There are many posts in the papercreters message archives on the topic.

The more paper in your papercrete mix, the more compressing it can improve it's insuation capacity. The less paper and more sand, cement, clay, or other mineral content in your papercrete mix, compression will still improve it, but to a lesser degree as the mineral content of your papercrete mix goes up.

As with everything in life, the key is to find a balance. Use enough mineral content in papercrete to get the structural strength needed for the application intended and to inhibit mold growth, but not so much mineral content that your mix becomes more and more like concrete and eliminating it's insulation properties.

Furthermore, even cellulose insulation manufacturers promote "dense packed" cellulose insulation as a superior insulation to "loose packed." This phenomenon is not unique to papercrete, it applies to all forms of cellulose insulation.

The research you may have done may have captured the common misconception that cellulose and papercrete have similar properties to fiberglass. They do not.

I hope this explaination is helpful.

--- In papercreters@yahoogroups.com, "kjtbeskimo" <vickeym@...> wrote:
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> Sounds very interesting! However, I do have a questions in your description of the possible pros of using this method.
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> It is this sentence which confuses me:
> "The drained but damp papercrete could easily be tamped into place as the wall is built providing for some compression of the damp slurry which greatly enhances papercrete's strength as well as insulation qualities."
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> In all the research and reading we have done on papercrete compressing the blocks, bricks, walls, whatever you happen to be making it lessened the insulation value NOT increased it.
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> As with most insulation would it not be small air pockets which would provide the greatest insulation value (as long as you don't overdo it.)
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> Can you or anyone else please clarify this? To compress or not to compress...that is the question?
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> Vickey in Alaska
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>