Walt DeVore, Inventor
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Precast concrete wall panels are made in precise molds. 40% of the volume is displaced by embedded styrofoam. The average panels weighs only 40 pounds which is 15 pounds per square foot of wall face. This is the most economical use of concrete on Earth. These high strength panels can be easily handled and installed all day long.
Beveled edges convey the timeless aesthetic of cut stone. Panels are amenable to acid staining and integral dyeing for unique dramatic effect. They are fireproof and maintenance free.
A mold is as valuable as how much precision and features are imparted to the product. CBS molds impart precise dimensions, embedded styrofoam, embedded expanded steel fastening webs, and a chevron groove around the perimeter.
These are wall "faces", or one side of a two sided wall. They attach together in two modes to form a complete wall piece. The front is like beveled cut stone.
The "super" attributes are on the back side. There is no "standard" concrete accessory this type of coupling. The key insight is using "expanded steel" to make the embedded across the wall cavity connection. It's wide "footprint" is perfect for strong attachment. One could balk that steel would cause too much "thermal bridging", where heat or cool is too easily transmitted through a wall. There are six strands of steel involved per piece of expanded steel. Each strand is 1/10th ny 1/10 inch. That's a cross sectional surface area of 1/100 square inch. The six strands as a composite are then 6/100 square inch. Heat flow is measured in "k", a symbol that has a unit of per square foot. That makes the heat flow or thermal bridging value be 0.06 / 144 = 0.000412. This virtually miniscule amount can put to rest fears that a steel "across wall" fastening device will overly suffer from heat transfer.
All components have a continuous slot around the perimeter.
The molds are the heart of the process. They are designed to be precise and very easy to work.
The process is versatile. It can be picked up and executed immediately by unskilled people, with minimal supervision. The main requirement is that it be done indoors in as controlled environment as possible. Uniformity of conditions supports consistency that assures consistent concrete properties for critical quality control.
The act of empowering people for their advantage is the true definition of wealth. There is ample resource to provide for everyone. A
The expanded steels overlap in the wall cavity. They are simply and quickly tack welded with a 115 volt wire feed welder. The strands are easy to weld with a quick zap from the welder. This type of welder is very easy to use and one can practice to quickly gain proficiency. Self darkening welding helmuts are another contributing aid.
The system is amenable also to automation, depending on application and availability of resources. There is no other way to use such minimal concrete to supreme advantage. Groups, neighborhoods, family, and friends can contribute in a fun social activity to propel the process along. Simple wall diagrams show exactly what to do.
Roofs are a prime target for vast improvement. Sheathing, tar paper, and shingles in my opinion border on the absurd. When hail can trash one's roof and cause tens of thousands dollars damage, there has to be a better way. They are ugly in natural landscapes. On the Front Range in Colorado as developments go to the foothills, the pointy roof lines degrade the natural beauty and integrity massively.
Completed construction with Concrete Building System wall panels. CBS homes appraise for more than their cost of construction due to the quality, precision, and efficiency of the system. Instant hefty equity is immediate as learned from experience. This is a concrete cavity wall system, with cast in place concrete and insulation encased within the wall cavity. Walls are inherently fire proof, water and wind proof, and immune to ultra violet degradation over time.
"Stick" construction begins pulling apart as soon as it's assembled, due to shrink swell from humidity and temperature differentials.
Cast in place concrete is part of the interior thermal mass. This insures mimimal fluctuation. 24" x 16" is the prevalent panel size and weighs 40 pounds, 15 pounds per square foot (2-2/3 sq feet).
Under construction in Roberts Creek, British Columbia. Designed and constructed by Rob Milsted, RDM Designs. Panels made and supplied by Walter DeVore and helpers. The large window openings were possible despite the building code (California stringency) and engineered plan being in a maximum design criticality for earthquakes along the BC coast.
Windows without CBS frames. More work to contain cast in place concrete as it requires demanding bracing. This method may be a cleaner, high end aesthetic depending upon the observer.
This was the first home build in Canada. On site yellow cedar was incorporated to complement the concrete. The system can hybridize with conventional construction. This concrete option is a new value option in a designer's repertoire.
Lintel pieces over openings are temporarily supported. The embedded steels on the back of the lintel are encased in concrete during the cast in place structural fill. Deep beams are simply formed within the wall cavity for any load.
Our first work in BC. Different release agents were tested for use with cellular concrete. The detergent quality of wet cellular concrete would dissolve the release. This eventually lead to the abandonment of lightweight cellular concrete. Using regular pea gravel concrete solved release issues. I formulated a new strategy of using 40% less concrete with a "void" system instead of 40% lighter concrete. A good decision.
This project endured inconsistent extrusion widths for the molds. Sometimes a custom size panel was necessary to keep the panel joints tight. It was an easy end of day task so the panel would be ready at the beginning of the next day. A new generation of molds was created to remedy the problem. Precision is not easy and not to be taken for granted. My experience has showed me the simplest way to solve the "devil in the details". These solutions will be discussed later.
Corner quoins maintain the aesthetic of solid block walls. These corners can be challenging for the precaster. All three planes, the x,y, and z, must be perfect. This degree of precision is facilitated by an assembly jig. Experience shows the best way to do it. Aptitude in geometry is a must.
The standard rebar specification for openings up to 11' is two #5 rebars top and two bottom, Grade 60, with #3 stirrups on 12" centers. The "beam" is 8" wide and 16" deep. Beam depth can be up to the height of the wall above the opening. Here, two 8" high lintels make a 16" deep beam.
It was the designer's choice, Rob Milsted, of RDM Designs, in Sechelt, BC, to not use the regular system door and window frames. He chose to have separate forming to contain the interior cast in place concrete. Then the two inch thickness of the frames was removed. It's a matter of preference and budget. CBS offers the opportunity to have components for all conditions of "stay in place" concrete forming pieces.
Note on the bottom row there are some non standard size panels. Making molds or using regular molds as adjustable molds is easily done. When one faces a design challenge of not being able to eliminate vertical seams from being aligned over each other, the panel size can be adjusted.
This area in British Columbia about a hundred years ago was consumed by fire. When it happens again, the concrete walls should be fine. Fire resistance is also dependent the interior furnishings.
Wood rafters are common but a post tensioned slab is preferable. Slabs need to be at least 35' long before post tensioning is recommended to gain enough "tendon" elongation. A little is lost during the seating of wedges that grip the tendon. (A tendon is the high strength steel cable of 270K pounds per square inch yield strength that is sleeved within a plastic wrap to allow the cable to slide and tighten independent of the concrete.)
Wood on concrete doesn't feel right to me, but in this addition is necessary to tie into existing structure.
My very first project from 30 years ago. Terra cotta acid wall stain gives a non concrete look. It is still maintenance free today.
This studio in Lakewood, Colorado did not require any wall fill concrete except for a 7" deep bond beam at the top of wall. There are four 3/4" threaded rods from the footing through the bond beam to hold the truss roof down. The wall cavity was filled with recycled styrofoam beads, "regrind". A contractor did the slab and in routine manner attained a flatness for the first row of panels that was problem free. My sister and I did the majority of the work.
A standard window frame into a 48" x 48" opening, with two inch thick cast frame pieces for a window size of 44" x 44".
Door frames are 44" wide and 86". Standard doors can be framed. Threaded inserts and a hinge plates can be added to the door frame. Door hinges can be directly bolted. Manufacturing doors for the system is another business.
Wood carvings (on lintel above window) and other works of art can have rubber molds made and then placed into molds. Fine art is easily added.
With one, two, and three feet long wall panels symmetry and proportionate design facilitates simple easy interest.
My laboratory. A steep mountainside home under construction in the mountains of Colorado.
Octagons with equal wall lengths would be the easiest and most efficient shapes to build.
Dear Reader,
This system has been my obsession since 1987. It came to me in bits and pieces during my frequent dog walks overlooking the Continental Divide. Mountains never cease to inspire.
I'm a Rambling Wreck Industrial Engineer, having graduated in 1973. Upon purchasing a mining claim on a steep remote mountainside, I began my building experience with rammed earth in 1983. Obsessive thinking gradually evolved this system from impossible fantasy to functional reality.
I believe the fundamental advantages should make this a virtual no brainer opportunity to launch construction into a present day innovative solution.
These fundamentals are:
1. The component wall panels are a one step architectural finish, glass smooth, beveled edges, strategic concrete that emulates the timelessness of "cut stone".
2. Panels alone have substantial strength, especially when analyzed by American Concrete Institute equation
3. Concrete volume is displaced 40% by embedding styrofoam in non structural critical areas in the back side of the panels.
4. Pieces of expanded steel are embedded in the wet cast panels providing a perfect connection between wall faces.
5. A continuous wall cavity can accommodate and contain any creative inside wall application.
6. Pieces are light enough (15 pounds per square foot) to manually handle and install.
7. Spline and slot (tongue and groove) installation is fast and foolproof.
8. Attention to precision gives tremendous return.
9. Reduced concrete and weight facilitates economy and durability.
10. Vulnerability to fire and climatic events is greatly reduced if not eliminated.
11. Standard materials and associated labor with wood, drywall, sheathing, siding, wrap, and paint reduce construction costs.
12. Homes appraise significantly higher than construction costs.
13. Patented (5,802,793) concrete construction system
14. Opportunity for home owners, homesteaders, designers, concrete contractors, precast concrete shops, community industry
15. A new tool for greenhousing, water conservation, and gray water utilization.
Cellular Concrete
Using cellular concrete as the wall cavity fill can make wall insulating even easier. No rigid insulation boards need to be cut or fitted. Air infiltration is eliminated. The insulated parts of the wall are partitioned with osb board that after curing can be removed. Cast in place concrete is poured against the hardened faces of the cellular concrete. A complete solid monolithic composite is achieved.
Design Modifications to best use CBS
Replacing wood truss roofs with post tensioned slabs removes the weakest link in concrete homes, the wood shingle sloping roof of minimal utility. A pt slab is a diaphragm that monolithically ties all the walls together. It lets the roof be a patio with great utility and gives a vertical perspective looking out that refreshes one's spirit. There is an increased comraderie of seeing other people on their rooftop patios as the vertical supplement brings out good cheer. I experienced this on concrete roof top patios in Kathmandu. A fresher breeze and elevation over street sounds makes a big difference. It joins the rest of the concrete house in a maintenance free fire proof mode for a very long return on investment. The structures ability to withstand catastrophic forces is greatly enhanced.
The basic requirement for a post tensioned slab is that it be at least 35 feet long. The "tendons" that provide the strength are 270 KSI steel usually used in half inch diameter strands. The 35 feet is necessary so that when they're stretched with hydraulic jacks to impart the tension, the tendon stretch must be enough to not be lost when the "seating" wedges are applied to the strand and then it's relaxed a little to recede into it's conical retainer.
Devil in the Details
The big question associated with innovation is if it's so good, why wasn't it thought of before and in use now? There are several answers to this. I have developed this on my own, through a 35 year process of rumination and experimentation.
Having an engineering degree and not caring to work for weapons conglomerates, I needed to go my way, counter to "normalcy". I chose an off grid remote mining claim in the Colorado mountains. The fractured granite soil was perfect for "rammed earth", so with some help from a friend, I got a tractor to generate and handle piles of dirt. How glorious it felt to be pounding dirt into walls.
Duty to my dogs had me doing countless walks overlooking the Continental Divide, where I felt the quartz in the granite pushing my thinking forward. Ideas came in unexpected "Eureka" moments, and built upon each other. My rammed earth walls required attachment of rigid insulation to the exterior faces, thinking that would keep all that compacted dirt as part of an interior thermal mass. There was no good way to nail up sheets of polyiso to dirt. Then after making that tenuous connection, I put up chicken wire, mixed cement and sand, and "stuccoed" over the iso. It was a brave experiment that worked just good enough for a not real long time.
But the image was in incubation, a cementious wall face, insulation, wall substance, and for symmetry, a plastered inside wall too. My Hoover dam era Jaeger concrete mixer worked me to a frazzle, lugging five gallon buckets of concrete into my tractor bucket, raising it to roof level, and dumping onto my roof form. I realized if I left space for big skylights, the amount of concrete could be lessened. I was not smart enough to not fill buckets all the way up to lighten their weight.
The idea for the system started coming in. The mental images did not reveal a workable geometry, but then that began to formulate. I realized it was indeed possible and began thinking about molds for the wall panels. Seemed lightweight concrete was the key. Reducing the weight of the panels 40% was the only way to make them manageable. There was an expanded pumice plant not too far from my place. I have an old 1970 Chevy flat bed truck that's survived the ages so I'd take it to the plant and load up five to six thousand pounds of "block mix" aggregate. I had gathered a bevy of five gallon buckets so upon arrival I'd un-nest them and set them out to be filled from the loading tractor bucket. Every bit of ahead of the game helps.
The last two miles back was a wash board dirt road that started at 7,000 feet and I turned off it at 9,000 feet. I affectionately called it "Lose your Load Road". Fortunately I survived countless sojourns.
FAQ
What is Concrete Building System (CBS)?
It's the end of building structures with sticks The establishment of personal sanctuary. The engagement of all to establish individual freedom, self sufficiency. A doable path to housing everyone on the planet well. A response to "a poor man shames us all"
What makes it work?
Precision and minimal concrete. Often 70% of a concrete project is in the forming costs. With CBS these costs are eliminated, greatly enhancing the economy and viability of concrete construction.
How difficult is the precision?
By using jigs and molds, reaching precision once can then be imparted to raw stock virtually infinitely. A precise surface is too easily taken for granted and is actually impossible to achieve. One can only get closer with continuous refinement.
What is the best bulk material to achieve a nearly perfect surface?
Concrete. In its plastic state it can be screeded and troweled with laser precision by skilled experienced concrete "finishers".
How is a perfect surface utilized?
It serves as the base for precise precast panels to be placed so the first row of panels has perfectly flush and horizontal top surface. There are usually slight undulations. They need to be average out so that for each foot length of slab, the "crests" of the undulations are close enough together and equal in height so the panel sits perfectly level. Then more rows are built up in precise manner to complete a wall. One starts right to finish right. It's easier said than done.
How is a wall started precisely in line?
The wall panels have an eighth inch wide slot 3/8" deep. One uses a concrete saw to cut slots into the slab or footing that are 1/8" wide and 3/8" deep. A spline is placed in the slab slot and then the wall panels sit on top of the spline via their corresponding slot.
How does one recover if the slab or footing is not flat, but has undulations in it?
It's a somewhat painstaking problem but has an excellent solution. One eighth inch thick steel bar is available in many increments of height, e.g., 1", 1-1/4", 1-1/2" etc. One cuts (saws) the slot into the slab to denote the wall location. The slot can be deepened with a concrete diamond blade in a circular saw to level out the bottom of the slot. Then the steel bar is installed so the top of the bar is perfectly level. Wall panels will then attain that level.
What makes the wall panels unique?
It's in the molds and precasting process. A minimum number of sizes of panels are used for maximum design versatility. Symmetry can be maintained by using 12", 24", and 36" panels. Molds are trued before addition of concrete to guarantee their precise uniformity. More on molds later.
How is a minimum amount of concrete achieved?
The minimum thickness of a panel is two inches for structural stability. This thickness is maintained around the perimeter and along vertical ribs. The space in between has styrofoam pieces used as displacement blocks that reduce the panel thickness. With steel and synthetic fibers to enhance structural strength, thicknesses to one half inch can be achieved. The styrofoam blocks leave no "shadow" of their presence on the outside panel face.
Why is a "cavity" wall the best wall?
Custom sized pieces of expanded steel are embedded into the panel back side centered on vertical ribs. Wall panel back faces have the expanded steel project out and overlap with its opposite mate, creating a cavity wall of any width. The overlapped expanded steels are simply tack welded together for rigid permanent joinery. Within the cavity, versatility abounds. From simply filling with onsite bulk dirt to rigid insulation and reinforced concrete, or filling with cellular concrete, using as an air duct, evaporative cooling, gray water processing, virtually anything can be done, especially in the "green" domain.
Steel studs are easily attached to CBS walls with Tapcon screws. Attachments are best made where screws can penetrate the two inch panel thickness. These are the two inches at the top and bottom of each panel, and the two inch deep vertical ribs where expanded steels are embedded.
Panels can be cast with access doors to reach the interior cavity. Panels can be left out on one side of the wall for built in cabinets and shelving. (The expanded steels are left out of the opposite panel)
What is different between CBS and ICF's (insulated concrete forms)?
With ICF's the durability of exposure of concrete in wasted. Traditional vulnerable wall coverings are still needed, along with their labor. The styrofoam concrete containment is tenuous and needs substantial bracing. There is no bracing with CBS walls. The cut stone aesthetic and glass smooth surface gives a finished architectural finish in one step. Window and door frames can be dyed a different color from the wall panels for a clean elegant look. One example would be using terra cotta stain or dye on wall panels and turquoise stain on frames before installation.
What kind of roofs and ceilings are best used with CBS?
Post tensioned concrete roofs are the best utilization of concrete in a horizontal application. The only restriction is the total slab length needs to be 35'at minimum to stretch the tendons and have them seat with proper tension. Flat post tensioned roofs give a more natural blending into the environment. They turn roof space into the potential for roof top patios, for gardening, entertaining, and easy safe solar equipment access. Slab thickness can be reduced to the longest distance between supports divided by 45. A six inch slab can be used for up to a 22' span. In regular housing where the depth of the house is close to two 14' rooms or 28', design can be expanded out at least another 7'. All or part of that extension can be the addition of an attached south wall green house.
A CBS wall supporting a slab can be a form for a perimeter spandrel beam to the slab for added stiffness. This forming action is part of system and completely free.
How fireproof is CBS?
Fires are tragic events. Stick houses, according to my Denver fire fighter friend, have about 7 minutes to be saved. CBS with concrete wall faces and an internal cast in place structural system, insulated on its exterior side, are a composite that couldn't be more fire resistant. The fuel supporting a fire, especially if the structure isn't the fuel, would likely be consumed before damage would set in. It depends on the environment of course, but the CBS composite is many times safer and more survivable than sticks.
Where is CBS now?
I have developed and worked with my CBS over 30 years. I have enacted new techniques and built several structures. My last stint was in British Columbia. It's now time to turn this over to younger fresher bodies. It would be a huge opportunity I believe for the right person. I have the necessary molds, conveyors, and carts for the material handling. My Hoover Dam era mixer has given great service, but really isn't the right mixer.
What is needed now is an inside place to precast the product, where temperature and humidity can be controlled within reasonable limits. I believe the best mixer is a volumetric mixer, so the age of the concrete mix deposited into molds is uniform. A truck mounted mixer could do outside work of foundations and slabs in the morning, and then mold filling in the afternoon.
To estimate space requirements for a CBS operation, one can estimate the amount of panel required for a home to be 3.3 times the floor plan area. So a 2,000 square foot house would require about 6,600 square feet of panel. A precast plant floor can have 1/3 the area dedicated for panel storage and movement. This is best accomplished by having molds on carts, about 5 molds per cart, with 5 inch casters, for easy moving and butted together for compact storage.
CBS needs a development, an architect/structural engineer, a precasting facility that could be an onsite quonset hut, and a concrete contractor large enough for the work. I suggest crews split time between site work and precasting in order to experience and appreciate the interdependency of the work.
Crew proficiency can be rewarded by expansion into more crew leaders. The superior construction can expand globally requiring experienced people for leadership.
More Subtle Advantages
The wall panels are used to their utmost structural efficiency. Structural stiffness increases with the cube of the distance from the neutral axis. The wide footprint the wall faces create contributes a large amount of stiffness per volume of concrete used. This is quite significant.
To minimize the amount of "embodied energy" that is used to judge "green" content of structures, the wall cavity may contain sand or plain dirt. The volume of the cavity for a 12" wide wall is double the volume of both wall faces. Therefore, for each unit volume of wall, one can get two units of bulk fill. That is huge.
To have a flat post tensioned roof, one can have all the roof area for elevated patio, solar access, and gardening. The greater vertical from being on the the patio contributes to one's sense of spaciousness.
Wall panels may be used without the embedded steels to make 2" wide walls for closet enclosures or other partitions. With the slot and spline attachment, and construction urethane adhesive, the cut stone aesthetic can be maintained. The panel backside of the styrofoam embedment can be plastered, stuccoed, or textured over. Electrical conduit can be used on the wall face.
Panels may also be attached to steel stud framing for any amount of projection. This can create more inner wall space and facilitate conduit and piping runs.
High rise construction can be revamped by building the walls first on any story, and then pouring columns and beams within the walls. This would eliminate supplemental forming.
Panels may be used horizontally as a stay in place elevated slab form. They could be supported on 24" or 16" centers with TJI's, I beams, or steel trusses. There needs to be 2" of cover to post tensioning tendons for fire rating. The panels staying in place can provide that. The embedded expanded steels, now pointing up, can provide precise positioning and tieing for PT tendons.
Benefit of Mass Wall, Conservation of Momentum, Fundamental Law of Physics
Anything in motion, wind, water, or Earth, has momentum equal to its mass times its velocity. So when a moving mass strikes a wall, the mass of the wall absorbs the transfered momentum and damps the deformation. This is beneficial in catastrophic events, and blast protection.
There is so much more, enough for now.
Link to viewable spreadsheet with basic numbers
Video to orient to spreadsheet
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