A lot of research has been made about the additives used to the mix, as they are the biggest drawback to the materials green status. Additives:

should not increase the price of the mix and

they have to be tested for long term exposure in outside environmental conditions.

further  research is needed towards ecological friendly insulating materials.


Papercrete is hydrophilic material. It has an affinity for water and it acts like a sponge unless it is coated with something to stop the entry of water.
There are several possibilities to waterproof papercrete. Silicone-based formulas that are absorbed into the papercrete seem to work well. Another option is Geobond, which could provide a fast, durable solution to sealing, fireproofing, and scuff-proofing papercrete
When water goes into untreated papercrete, it quickly evaporates. It absorbs water but it doesn’t lose its shape. Papercrete becomes temporarily heavier, but as long as it can shed the water through evaporation (in other words as long as it can breathe) the water is not harmful.
The potential problem with completely sealing both sides is that if moisture does get in there somehow, it can’t escape. If the water is trapped and retained inside the papercrete wall, mold, mildew, fungus, etc. may take hold. That’s why it’s best to either let the material breathe or moisture proof it completely.

Fire retardant

Papercrete has only been informal tested on fire. A mix of boric acid and borax is most commonly use to fireproof papercrete.   Adding more sand also increases fire retardancy.
The untreated mix smoulders like charcoal and eventually burn, unless we add a significant percentage of non-flammable material. Different mixes burn differently.
The term “flame retardant” has to be differentiated from “fireproof.” Smouldering with no flame is considered flame retardant.  Being only flame retardant could result in an unlikely but dangerous scenario. Papercrete would not continue to smoulder for long because of lack of oxygen.
Using fireproof mortar between the blocks and fireproof stucco  on the outside will  limit a smouldering fire to the destruction of only one block.
But for all practical purposes, papercrete is relatively safe (safe as or safer than wood) without being treated. It’s even more safe with the boric acid solution above


Colorants can be added to the mix during the process of making the mix or can be sprayed in the final surface after it gets dry. Powdered charcoal, iron oxide paints, emulsion paint or core materials can be used. Some colours might have problems with draining out of water with papercrete capturing water inside the wall and creating problems with moisture.



About Menelaos Kokkinos

Menelaos Kokkinos TU Delft
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