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I know this has been asked before, but I wanted to re-raise for discussion the idea of using lava rock in building walls for a house. Specifically, I am interested in people's thoughts on the feasibility of slipforming with lava rock as a way to combine the benefits of local materials (low cost / high availability, island aesthetic) with the strengths of reinforced concrete walls (high durability, ease of construction, etc).
In brief, slipforming uses short wooden forms (~2' usually) which are filled with stone on the face, then back filled with reinforced concrete. Once the wall is set, the forms are then "slipped" up to the next level and the process is repeated. The end result is a wall that has rock outside and reinforced concrete inside which can be roofed and finished like any other concrete wall. As the technique is designed for owner/builders and uses minimal equipment there are obvious cost savings, although lots of time/labor has to be spent building.
Slipforming info:
Overview:
http://www.hollowtop.com/cls_html/masonry.htm
In depth:
http://www.motherearthnews.com/Do-It-You...pform.aspx
Daughter and Father build Stone house:
http://www.hollowtop.com/cls_html/stone_home.htm
Given what appears to be lots of structural lava wall examples in the area (retaining walls, some stem walls, Hilo public library?, etc) I'm always a bit confused when I'm on island why there are not more house walls built using lava rock. Feedback is much appreciated especially from anyone with experience building with lava rock or ICF/Rastra, etc...
Sorry for the long post and many thanks!
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You may want to check out the UHH Performing Arts Center
www.uhh.hawaii.edu - although they did have sonme face rocks pop off after the '06 earthquake.... Oh, and local rock work is not a way to save money... unless you have & do the work
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Just don't neglect the rebar and remember that lava rock is very fragile structurally. Also, heavy masonry as you describe has a high thermal mass effect which may not serve you well here depending on the altitude of your location. Upper elevations better. Lower elevations worse. I would also be careful about the heights of the walls and their lateral design. Earthquakes are serious things and the buildings structural design needs to be correct.
Best wishes.
Assume the best and ask questions.
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One of the main reasons there aren't that many concrete or brick houses is the amount of earthquakes we have around here. A monolithic pier or post for a porch is a lot different than the whole house. Concrete has great compaction strength and very low tensile strength. Earthquakes shake and twist things, not squish them so all concrete construction isn't one of the top choices in an earthquake zone.
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Kurt Wilson
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Kurt Wilson
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Thanks for the feedback everyone!
Carey - I'll definitely check out the Performing Arts Center when I'm back on island later in the year. Always good to find more examples to study! And yeah, we have the rock and the emphasis is most certainly on owner/BUILDER [
]
HotCatz - Earthquakes are
the major concern with this approach. Because of this risk, I originally wrote-off reinforced concrete walls altogether but keep running across projects that make me reconsider such as:
CastleBlock/Rastra (of course!)
http://castleblock.com/rastra.html
ICF Construction
http://www.wdcicf.com/ICF-Construction.htm
Kehena Tower
http://book.bigislandvacationrentals.com...fault.aspx (10 yrs old now!)
etc...
Rob - The intended build site is mid-range elevation (Hawaiian Acres) so not too hot, not too cold (hopefully just right [
]) which has several shaded and unshaded possible house sites. The wall heights would be kept to one story (8-9' max) with both vertical and horizontal rebar (every 2' max). Also, looking at vinyl bucks such as
http://www.vbuck.com/ and a steel shed-style roof to avoid wood altogether. Of course, it can't hurt to involve a structural engineer/architect with reinforced concrete/ICF experience to review these plans if anyone has recommendations.
Overall, I really like ICF, with the exception being the need to finish the walls inside and out. Be nice (if possible) to integrate some local materials to create a more finished wall during the initial wall construction.
Thanks for all the input!
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A properly reinforced concrete wall will out perform wood frame every day. But I want to emphasize a proper design and rebar placement.
The Rastra ICF line we handle, by example, was tested in a seismic rack and compared to wood frame for measured force to fail it's load carrying ability and whether that failure was gradual or catastrophic.
Results from U.C. Irvine:
Failure at:
Wood Frame = 9 kps
Rastra = 84 kps
Rastra out performed wood frame with plywood shear wall by a factor of nine.
Failure type:
Wood Frame = catastrophic
Rastra = gradual
These types of structural failures mean one one hand you likely die and on the other hand you likely have time to run out of the building.
I participated in these tests at U.C. Irvine and that experience plus my experience as Construction Chief for Habitat for Humanity for the Northridge Earthquake (1991) left me with very low regard for wood frame housing especially as practiced by our mostly jackleg, don't quite know their trade carpenters. But everyone gets to make their own choices.
Assume the best and ask questions.
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The slipform idea will not save you time or money.
but well designed reinforced concrete can take anything you can throw at it. you can get texture molds/liners to go in the forms so you can make it look like stone walls. or go with thin shell ferocement there is a product(called tripanel i think) if you need insulation
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The emphasis on proper design is clear - any suggestions on who would be able to help with getting it right?
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In most locales an engineer is required for reinforced concrete construction. Here in Hawaii County all you need in an architect. But you do need an architect familiar with concrete design and most archs here are stick frame people with some light foundation experience.
One of our Punaweb members whose user name is John the Architect is very familiar with concrete design and you could start with him.
Assume the best and ask questions.
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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.
