Posted: 8/9/2009 1:30:31 PM EDT
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Watching the locals here in Bahrain build houses basically using the dry stack method. What would be the issues of using same construction in US?
Concrete blocks don't have much insullation value I assume. Would a vapor barrier be needed on the inside walls? Houses over here have no material on inside wall besides tiles or paint. |
| issues would be code violations and lack of strength. CBS walls are not very strong without mortar and vertical solid poured cells all connected with a horizontal tie beam. Insulation in tropical climates like florida is often just a vapor barrier in lower end construction. Higher end homes often have spray foam insulation or foam board panels laid over the block and then furring strips or a 2nd wall built over them |
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The dry stack I've seen in the US is filled with rebar both vertically and horizontally and then all openings are filled with mortar. That seems pretty strong.
The dry stack block openings here are filled with concrete/mortar and each opening has rebar running the entire height of the wall. They lay a prefab concrete roof on top of the walls, wire the rebar of the roof panels and the walls together and then lay a small layer of concrete across the entire roof. This joins the walls and the roof together as one piece. |
| Surface bonding cement is probably another option depending on code in your area. I've used it on seawalls and on a garage and it's worked perfectly. Downside is it's kinda expensive but upside is that it's damn quick, can even be sprayed on with the right equipment. |
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There is a guy in Austin who did a blow-by-blow picture essay on his version of dry stacked block construction HERE. "Mother Earth News" has articles, as does Texas Tech tornado labs. There was even a company from Virginia, which had a dry stack type CMU roofing system, "BlockJoist". They had specially constructed web steel joists that were mortared into the composite of CMU blocks.
I have been a fan of the method. Walking through some national parks, I saw split-faced cinderblocks dry stacked. Every other void was filled and reinforced. I was thinking of using that method to construct a fence. The surface-bonding cement is both structural and waterproofing. If you want to use the mass as a thermal sink, then insulation is outside of the envelope. Just as condensation collects on the outside of a toilet tank, warm moist air coming in contact with cooler CMU walls will cause condensation. Toilet tank insulation kits put the insulating barrier inside the tank, next to the larger thermal mass. There are underground and bermed homes in Oklahoma; one just south of Norman. If possible, ask these owners of their issues. I live in dry West Texas, and even here, a friend's CMU house has problems with damp walls and mold/mildew. Untreated CMU blocks are porous. Wind driven rain will penetrate them. Keeping the moisture external to the blocks is preferred. Since CMU construction has been around so long, like stick-built stud construction, there are common practices which need no engineering to meet code. I have a ream box full of information gathered over a number of years. I R a fan of this stuff. I like it 'cause one guy can do it. Ya don't need no degree to git it right or git- r-dun. (Sorry. My West-Texas accent surfaced). If done right, this stuff is like a bomb shelter... good news for those who live in tornado alley. Some forms of safe-rooms are made this way. If there were a way to insure consistent hydration of the mortar in the voids, the whole thing could be build "dry" and then a sprinkler system set up to bath the walls. There are retaining wall systems which are no more than bags of cement stacked and left for mother-nature to harden. The CAF has a flak gun emplacement with cement "sandbags"... made from lowly bags of cement. but I digress... CMU strength is only in compression. Mortar simply levels the individual blocks, eliminating pressure points by spreading the load along the entire edge. Dry stacked blocks often have areas of minimal contact where one edge bridges a defect. Surface bonding in conjunction with filling some of the voids helps to move the compression loads around these weak points. Of course, filling the voids becomes problematic, often needing a cement pumper truck to fill the voids and special vibrators inserted a specified levels during the pour. I suppose the voids could be filled as courses were completed, since their purpose is not to "glue" the structure together, but form a path for compression loads. Rebar inserted, if surface bonding is used, is just insurance as the fibers in the SBC provide the tensile strength. There is a wealth of free information out there on this construction method. Good reading. buckmeister |
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You have me searching through my "stuff". Here's a link to the Texas Tech study on projectile damage to the roofing system I referenced. Additionally, the system can support the weight of a vehicle (100+ lbs per square foot). You asked in another thread about cheapest construction techniques, by far the cheapest per square foot would be Geodesic domes. These do require a great bit of care and precision during construction. There are DIY kits using proprietary joints, as well as complete bolt-together kits. Domes are inherently strong, but are not discrete. Roofing them is problematic. CMU is next in line of cheap systems.
buckmeister |