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  • RE: Rocket Mass Heaters

    According the rocket mass heater theory as I understand it, the best place and time to get power for your system is the riser itself. The force of movement generated in the riser will draw in the fresh oxygenated air and push out the exhaust. After the exhaust gas has cooled, it is considered counterproductive to direct it upward against gravity. The power of the riser is significantly increased by every inch of its height and by each additional 100ºF. The more power a riser produces, the longer it's horizontal exhaust can be, the more heat can be extracted into the mass.

    posted in General Discussion
  • RE: aircrete vs. ferrocement

    @claudettn said:

    there is always the risk that the aircrete blocks are not done the right way and you have no way to test their quality...

    ASTM (pka American Society for Testing and Materials) has fully addressed aircrete, referring to it as Cellular Concrete.

    posted in AirCrete
  • RE: Rocket Mass Heaters

    In my opinion, the goals with a rocket mass heater are to:

    • Extract as much heat energy as possible from the fuel
    • Release the cleanest exhaust possible
    • Store as much of that heat in the home as possible

    These goals can be realistically achieved in the upper 90th percentiles using known techniques as established by CobCottage and others. Releasing clean exhaust is a BIG deal when living in a tight village setting.

    posted in General Discussion
  • RE: Rocket Mass Heaters

    The best built rocket mass heaters I've seen have super hot fires in insulated boxes to burn the fuel as cleanly and effectively as possible (hotter fire = more mass is converted to heat energy = less smoke emissions). Fireboxes that are wrapped with thermal mass actually cool down the fire - not the best place/time to extract the heat. The insulated riser powers the intake and exhaust flow so that the super-heated gas has plenty opportunity to then run through a thermal mass storage bank before exiting the building cool and clean. The best system I ever used would burn so clean yet extract so much heat that when the exhaust finally came out of the house (knee high off the ground) I could put my face directly into the exhaust and breathe it in*. The air exited the building at about 95ºF after running through some 40' of lateral cob benches.

    *Not recommended

    posted in General Discussion
  • RE: manuals with information from the workshops

    @Danielcancun Good question. Students automatically receive this information about 2 weeks before the workshop begins.

    posted in Workshops
  • RE: FAUX ROCK HOBBIT CAVE HOUSE?

    Great inspiration. There are many conversations on this forum on this topic. Here is one of my favorites: Aircrete and earth-berming

    posted in General Discussion
  • RE: Workshop Philippines

    The best way to get the latest info on workshops is to subscribe to the mailing list. They usually send out about one letter per month and usually the main news is workshop announcements. To subscribe click here.

    posted in Workshops
  • RE: Workshop Philippines

    I've heard that the 2019 workshop calendar has been settled. However, the exact locations are not being shared publicly yet. Domegaia did a workshop there a while back. Not sure when the next one will be.

    posted in Workshops
  • RE: aircrete vs. ferrocement

    Randy and Kathy Johnson have had great success with their pure aircrete patio, but overall I think it's best to top an aircrete walking surface with a 1/2 to 1 inch coat of concrete. I did one recently using coarse gravel in the top coat. If I were to do it again I would use fine gravel or sand only so that I could keep the thickness down to 1/2" or so.

    posted in AirCrete
  • RE: aircrete vs. ferrocement

    Aircrete is not waterproof - it does wick water to a certain degree. It has been demonstrated to float for years, which has created some confusion about being waterproof. It is mentioned on the site as being "waterproof, fireproof, termite proof, rot proof" which is to say that water doesn't hurt it, as compared to say drywall and particle board. The statement could be misleading for some, but I think it's not intended to be.

    Perhaps a waterproofing agent could be added to aircrete. Might be worth an experiment.

    I don't think that water absorbed into aircrete would cause freeze cracking. This is suggested by the fact that it floats for years - it continues to contain enough air to remain flexible against freezing. These videos furhter support the notion: Freezing Wet Aircrete Blocks and Aircrete Patio Spring Assessment

    posted in AirCrete