NEZ'S HYPARS

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This section was submitted by Gary Olsen  gobug@aol.com. Thanks, Gary!


The following pictures, while small, show the basic steps to building thin shell latex concrete hyperbolic parabaloids. Thanks to George Nez for generously sharing his knowledge and innovations in this simple process. For slightly larger photos and a little more explanation you can visit the following site: ________ . For enough detail to do it yourself buy George's book: ________

Additional Photos


Rigid Frame


A rigid frame is essential. The inset photo is a scale model showing the basic structure. The model shows ½ of the roof. Each half-roof is 2 hypars connected along one edge. Each half-roof is narrow enough to fit on a truck without special traffic accommodations. Extra diagonal braces have been added in the full size roof framing. Each strut is a 2x6 topped with a 2x4 (T-shaped). Each corner has a plywood gusset. The two halves will be joined together and lifted onto posts.


Attach the Stucco Mesh

A wooden frame allows using a staple gun to attach the netting. The lacing is started in the lower corner. One hypar is laced at a time. The first strip of nylon stucco mesh is pulled taut partly overlapping onto the fascia (not too tight). The second strip starts in the same corner and runs in the other direction. Strips alternate to the top with care being taken to avoid wrinkles or sags.


Apply Concrete Slurry

A slurry of acrylic admix plus Portland cement is first painted on the fascia and then dumped through the hole at the top and a plastic bristle broom is used to spread it over the surface. The underside is brushed and more slurry added as needed to insure the mesh is completely immersed in the slurry.


Many Shapes are Possible

Hypars can be connected to form many shapes. The top photo shows a smaller example using EMT tubing and welding the frame. The mesh was self-adhesive, and contact cement was used on the struts. The bottom left photo shows small models made with a thin film by Peter Payne. Each of the three green shapes is actually 6 connected hypars. The bottom right photo shows Peter and Ela finishing a bamboo and drywall mesh tape 6 sided hypar.


Cylindrical Hypars

These photos are cylindrical thin shell concrete hypars. Drywall mesh tape and contact cement were used to hold the mesh to the hoops. The lacing is similar to warped plane hypars. The waist is tighter on the top hypar because the lacing angle was greater. The bottom hypar is being used as a 55 gallon water container. It is made with 2 hula hoops and a roll or drywall mesh tape.

Questions and answers

The "netting " is stucco mesh? Can you use anything else?
Window screen works. G. Nez had natives sew linen from rice bags into strips and that worked too. His book describes a process for testing the strength of the material to calculate how many layers to hold the cement. With stucco mesh, even one layer would be strong enough.

What is an approx recipe for the concrete slurry?
Enough acrylic to make it brushable. If there is too much Portland, the mix won't brush. If it's too soupy, it drips through. George says you must have 10-15% acrylic to Portland. The stuff we used was 25% in the container. So that's just over 2 pounds per gallon of acrylic mix. So one gallon of acrylic per 20-30 pounds of portland.

So you need somebody inside the form when dumping on the slurry?
No. But, this is partly dependent on the weave of whatever you use. At Loraine I used a pretty open weave mesh - I don't remember the numbers, but I increased the overlap so the slurry would get caught up in the mesh. You broom the top first. Then the underside. If the slurry is the right consistency, you get a cottage cheese look below. Brushing it out is important to remove air pockets and get good penetration. It's messy though. George wore a plastic grocery bag as a disposable hat.

You can end up with a desirable rough texture on the inside surface?
Yes

Once I have the hypar concrete membrane glued to 2X4's--how do I deal with it--how do I get it off the boards and onto the roof?
George stapled the mesh to the frame. In his design, the frame is part of the final assembly. It makes a square fascia, and a surface for a gutter, and support for a ceiling/attic space. The frame also provides surfaces to mount the shell on posts. There is some belief that the hypar would be structural without the frame, but no-one has tried that yet. I wanted to at Loraine this year but I didn’t have a chance. George transported the two halves on a flat bead, connected them on site, and had a crane lift it from the top of posts. His system for lifting it by hand uses several people to lift one corner, and someone else slides a pallet or 3 under the corner. His whole concept is done without electricity or power equipment.

If I use a metal frame I can't staple--so how do I attach mesh/netting?
If you use non-adhesive backed fabric, you can use contact cement on the frame and the fabric. The adhesives on drywall mesh tape and adhesive backed stucco mesh are compatible with contact cement so you only need to put the glue on the frame.

 

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