Wednesday, March 13, 2013

Hard Core Walls

Nuform© walls/forms during installation.
Note the internal webbing showing on each
side of the door.

On my most recent deployment to Afghanistan I had the opportunity to observe the construction of a concrete building using the Nuform© system. Nuform© uses a vinyl form that is set in place, filled with concrete, and then left to become both interior and exterior surfaces. The first time I ran into this system is when I read Christopher Alexander's A Pattern Language: Towns, Buildings, and Construction.

Alexander tackled the idea of concrete pored into stay-in-place forms in pattern number "218 Wall Membrane." (Alexander divided his chapters into "patterns" each pattern contained an idea, proofs for the idea, and conected patterns on both a larger and smaller scale.) His version used site constructed forms that would resemble conventional concrete forming, but with a material that would be suitable to leaving in place. Alexander recommended materials such as plywood, brick, and gypsum board as form/wall material. All of which I see as seriously flawed in this usage.

A soldier sliding a Nuform© section to extend a wall.

Additionally, Alexander advocated using chicken wire instead of rebar and lightweight concrete with wider walls to make up for the lower strength of the lighter concrete. In the Nuform© system it uses normal concrete on the runny side, rebar, and the vinyl of the forms creates an internal webbing that improves the bulging issues that are a construction nightmare on any concrete project.

I'm not saying that any of these points makes Nuform© a system I like. The 6 inch walls are just too narrow to get the concrete to settle. Even with the runniest concrete specifications allowed and dedicated beaters hitting the walls to shake the concrete down, empty spots were left in the forms when the concrete was cured. The echo in this building was the worst I have encountered in any construction project I have observed, the vinyl provided no noticeable sound dampening.

In either method, making the walls straight and avoiding bulges is difficult. The use of so much embedded energy with the concrete is also a concern, as is the potential for chemical burns on the workers skin from wet concrete being poured overhead. Especially low grade concrete from a developing nation. 

I wonder if the concept of a stay-in-place form would be better applied to a rammed earth building or even cob (although I can't see how a form could improve cob.) With both of these earth construction systems I would use even thicker walls than Alexander recommended. A form material would have to be found to work with the earthen materials, vinyl has a high energy footprint, just like the concrete. 

Any vertical use of concrete requires heavy support and
bracing until the concrete is set. The weight of the concrete
is enough to throw the whole project into a jumbled mess
without the extra help.

I'm not sure I will ever find solutions to the problems I am seeing, but by looking at them I become a better designer and a better problem solver. And if we are ever going to make the world a better place those are two things that all of us need.

1 comment:

  1. Have you seen the concrete tents they are coming out with? Soooo cool.