05-29-2009, 01:27 PM
One construction method that is similar to slipforming is tilt-up masonry construction. It is used extensively for commercial buildings like warehouses but not so much for homes. You lay out forms on the ground as though for a slab. You can also lay down rocks in the form prior to the pour so that their faces will be exposed afterwards. You then lay out a grid of rebar, again just like a slab. Pour the concrete, let cure, then get a big crane and tilt it up into place as a wall. Rebar is left to extend out the edges and is welded together where the walls meet, then more rocks are mortared in place to form the corners.
Sounds neat but it is on the ragged edge of owner-built because of the cranes and the need to really carefully design the walls to survive the lifting process. Also, to get the strength you need to plan for a solid thickness of concrete sufficient to stand alone. The rocks are decorative and should not extend deep into the wall, so you are not saving on any concrete. Seems to me the larger the rocks, the heavier the wall will be and the thicker the concrete part must be to support it so the rocks are sort of a negative when it comes to strength.
I think that slipforming would make a strong enough wall because of the rebar. Everything I have ever read says that it is materials cheap but labor intensive. I don't know about hawaii but slipform masonry seems to be received well enough by building departments since the end result is pretty much a reinforced concrete wall. I can also see how someone who is not dedicated could fail to get the rebar in the right places and I don't know of any such buildings in Hawaii. I don't think strength is the issue. It would be code compliance and whether the county could live with such a free-form process. I do know a guy who built a post and beam house with cord-wood infill. Cordwood is where you take sections of log about a foot long and build up a wall as though you were stacking firewood, mortaring it in place. In his case the logs shrank as they dried leaving each log a little loose. Still, it seems to be working out OK. My point is that if he could get a cordwood house permitted there should be hope for a slip-form masonry house.
I read about a panel of individuals down in Australia that was trying to evaluate construction techniques for their neck of the woods which was essentially tropical. They said that high thermal mass did not give great benefits there but it was OK as long as you kept it shaded. The concern is that it would soak up solar energy all day long and the house would be too warm by the end of the day and into the evening. My own personal experience in Eden Roc at 1,800' elevation is that I am more often too cold at night than too hot in the day. I think the thermal mass would help there but again, keep the sun off it. You would want big roof overhangs anyway to keep the rain off so I don't think it would be a problem if properly designed.
If you find an architect you can work with please post their name as I am also interested.
Sounds neat but it is on the ragged edge of owner-built because of the cranes and the need to really carefully design the walls to survive the lifting process. Also, to get the strength you need to plan for a solid thickness of concrete sufficient to stand alone. The rocks are decorative and should not extend deep into the wall, so you are not saving on any concrete. Seems to me the larger the rocks, the heavier the wall will be and the thicker the concrete part must be to support it so the rocks are sort of a negative when it comes to strength.
I think that slipforming would make a strong enough wall because of the rebar. Everything I have ever read says that it is materials cheap but labor intensive. I don't know about hawaii but slipform masonry seems to be received well enough by building departments since the end result is pretty much a reinforced concrete wall. I can also see how someone who is not dedicated could fail to get the rebar in the right places and I don't know of any such buildings in Hawaii. I don't think strength is the issue. It would be code compliance and whether the county could live with such a free-form process. I do know a guy who built a post and beam house with cord-wood infill. Cordwood is where you take sections of log about a foot long and build up a wall as though you were stacking firewood, mortaring it in place. In his case the logs shrank as they dried leaving each log a little loose. Still, it seems to be working out OK. My point is that if he could get a cordwood house permitted there should be hope for a slip-form masonry house.
I read about a panel of individuals down in Australia that was trying to evaluate construction techniques for their neck of the woods which was essentially tropical. They said that high thermal mass did not give great benefits there but it was OK as long as you kept it shaded. The concern is that it would soak up solar energy all day long and the house would be too warm by the end of the day and into the evening. My own personal experience in Eden Roc at 1,800' elevation is that I am more often too cold at night than too hot in the day. I think the thermal mass would help there but again, keep the sun off it. You would want big roof overhangs anyway to keep the rain off so I don't think it would be a problem if properly designed.
If you find an architect you can work with please post their name as I am also interested.