June 26, '09 Stripping and re-setting the formwork

We finished ramming on Wednesday, spent Thursday cleaning up, pulling all the screws that held the corners and VDB's in place, and laying out the kitchen floor to receive the form panels.  On Friday morning we pulled the she-bolts holding the forms together and the boom truck arrived on schedule at 10:00 am.

We lifted out the four inside corner form panels first.  Khyber and Gabe were on the deconstruction side; Rigo and Junior were on the form setting side.  It worked like clockwork, taking the deconstructors precisely as much time to rig a form for removal as it did the form setters to align and plumb each piece.  On the way to its new location, each form assembly took a short detour to the wash down area where Terra cleaned off the lingering debris with a pressure washer.

Four hours after we began, all eight of the panels were set, plumbed, aligned, and tied together, ready for the next wall installation.  We have another day or two of removing and resetting the VDB's and a day of electrical.  A week from Monday we'll plan on ramming earth again.

First Rammed Earth

Third week of June. Everything is in place for installation of the rammed earth in the first of the three buildings:  formwork is complete; electrical installed; reinforcing tied in place; soil formulation tested; sand, gravel, and clay blended; and the new conveyor delivery system built and ready.  The total volume  of loose material required for each of the modules is about forty yards, plus a three yard bond beam on top.  I thought there might be a chance that with eight people (two on the mixer, one on the delivery conveyor, four on rammers, and one as a  go-for) we could place all the material in one day.  We might have had it not been for a few slow downs with the equipment:  the mix was a little wet (even in June) and kept bridging in the hopper, and the newly invented rotating delivery conveyor needed some fine tuning.Things improved after lunch on the first day, and we finished mid afternoon on the second day.  We'll let the walls cure in the forms for two days, then loosen the clamps and she-bolts and bring in the boom truck to relocate the forms for the second set-up.The photos in the post illustrate the stockpile, finished formwork, and conveyor delivery system.  

Soil Preparation

Third week of June '09  Soil Preparation

The red clay soil from the excavation was going to be one of the primary components in the wall formulation.  I'll let Taj describe the process we went through to arrive at the final mix design.  For this post, I wanted to show you the screening plant we built to clean the soil stockpile.  

The red Calaveras Clay has a very high percentage of fines.  Most of the clods will break down into dust when chewed up, either with a mechanical pulverizer or the tires of the bobcat.  Since we wanted a dense wall surface with little chance of clay balls popping out during a freeze, it was necessary to both pulverize and to screen the soil.

We did this with a vibrating 1/2" screen mounted on a lightweight steel frame.  The bobcat fed the screen and a light conveyor belt stockpiled it.

The photos illustrate the equipment and the finished product.  In the background you can see the formwork nearly ready for the wall installation.

June '09  Installing electrical service in rammed earth walls:A quick post here to clarify how we get electrical service into the walls.  We use metal boxes (singles, doubles, and octagonals), fitted with terminal adapters as required.  The hard part is keeping the boxes where you want them against the forces of compaction working to drive them out of plumb.  You can see in the photos that the trick is a small wooden block, cut to fit inside the box, and screwed to the formwork.  Make sure the blocks are slightly back-beveled so they will come out of the box.  With the block in place, use tie wire to pull the box tight against the formwork.  Run conduit to connect outlets to switches to lights as required.  To keep the run lengths under control, we try to install eight inch or six inch junction boxes in a few key locations. Later in the project we'll illustrate how to install boxes for sconces and other lighting effects.

Wall forming building one

First week of June '09As soon as the floor had a few days of curing, we covered it with black plastic and plywood to protect it from damage.The forming system we decided to use on Terra's House is called Aluma System by Atlas Construction.  We were first exposed to this system when we built walls at the Las Vegas Springs Preserve.  It's actually been developed for large cast-in-place concrete walls, but we saw the value in using it for rammed earth.  We rented the system for a Cass Calder Smith project in Palo Alto, and then decided to buy our own components for Terra's House and the projects that would follow.  The big advantage to the Aluma system, besides that it is strong and light, is that once the large panels are constructed for a first time on the job, they can be moved from one set-up to the next with a small boom truck.  This can save a lot of man-hours if the project is designed to allow for repeating form set-ups.  We'll see how efficient it is as we move to the other rooms.I've assembled a set of photos to illustrate how the panels go together.  The horizontal members, called walers in forming jargon, are 5" deep aluminum I-beams.  The beams attach to the plywood form panels with screws.  We spaced them 15" apart.  Supporting the aluminum beams are aluminum strongbacks 7-1/2" deep.  The strongbacks attach to the beams with clips and bolts. Strongbacks are used in pairs, opposing each other across the wall, and held together with either she-bolts or taper ties.  We use she-bolts and 1/2" all-thread: one 12" off the floor, one at 6' off the floor, and then pipe clamps at the top above the wall.  Another advantage to this forming system is that the aluminum beams and strongbacks provide enough stiffness that only the three form ties, spaced 6' apart along the wall can resist deflection.  With fewer ties, there is more room in the formwork to allow easy movement for the rammers.The most complicated part of any formwork is the corners; straight sections are easy by comparison.  For the inside corners we butted the beams of the adjacent panels together, cut a narrow strip to fill in, then backed each corner with plywood gussets in between each beam.  The outside corners simply butt together, but we then backed each one with a custom wooden strongback and used long pipe clamps to reach all the way along each wall and pull opposing corners together.

Soil-Cement Finish Slab

posted by Taj Easton

 

Outline – Benefits of Approach

 

While trial and error has shown rammed earth floors to be somewhat impractical, we were determined to find an approach for this project that would allow us to maintain the natural and regionally appropriate aesthetic that would be created by the monolithic earth walls and ecologically sensitive design.

 

After careful pondering, we determined the best way to achieve this would be to pour a soil-cement slab, which would use the same locally-sourced clays that would constitute the primary component of the rammed earth walls as a coloring agent in the otherwise conventional concrete mix.

 

In conventional practice, this coloring would be achieved through the addition of chemical dies.  We found our approach to have many apparent benefits over the conventional approach.  These benefits included:

 

- cost (no chemical dies, slightly lower volumes of concrete required)

- environmental benefits [emissions (from transportation, die production, raw material extraction, etc.), reduce use of chemicals, removal of potential waste stream (if clay materials are extracted from the building site or nearby and will not have other uses), offset cement use]. 

- improved workability, slower set-times

- streamline aesthetics with local ecology and rammed earth walls

 

Process

 

Having extracted an abundance of red clay from the building site during excavation and road-building, we had acquired a large stockpile of a beautiful, red kaolin clay that we could use to add to our concrete mix.

 

We determined through testing that a conventional concrete mix with an additional 6% red clay would produce the aesthetic we were looking for, without significantly changing the character of the cement, reducing compressive strengths, or drastically increasing shrinkage.  We than calculated the amount of water that this clay would demand on top of the water demand for the raw concrete mix. 

 

In a 1 cu. yd. concrete mixer, we added approximately 18.5 cu. ft. of red clay (to give us the amount we would want to achieve our 6% target for one concrete truck).  We then added water to the clay and begin mixing, carefully measuring the water that was going in to the mix in five gallon buckets.  We continued adding water and mixing (approx. 45 minutes) until the result was a thin liquid slurry that would easily pass through a sump pump and 50 ft., 2” diameter flat hose. 

 

Having requested the concrete trucks to deliver a very dry mix, we then pumped this slurry into the concrete truck on-site using the aforementioned equipment (sump-pump and flat hoses - which we rented from a local rental yard).  When the clay slurry had all been added to the concrete mix, we than added the rest of the water that would get the final mix to its optimum moisture content.  This water was added directly to the small concrete mixer and pumped through the same system as the clay slurry, assuring that all of the red clay in the mixer itself and the pump lines would make it into the final mix.  We decided to play it safe on the dry side, so we could check the moisture of the mix after a few minutes of mixing and add more water inside the concrete truck if needed. 

 

The rest of the operation worked like a conventional concrete pour, with the exception of slower-setting times and improved workability.  As the slab dried, we were pleased to see the color blend seamlessly with the surrounding landscape and the stock-piled red clay that would soon be built into the house’s monolithic earth walls… 

Pouring the floors

Last week of May

With the special clay and concrete formula dialed in, the pour itself for the two north slabs went smoothly.  We ordered two trucks, each with 5-1/2 yards spaced four hours apart.  This gave us time to rough finish the first slab before having to pour the second.  After the second slab was laid down, it was back to the first one for steel trowelling.

The clay in the mix slows down the set time.  It also adds a "leathery" character to the finish.  Small micro cracking will occur over time.  With a sealer, this cracking can look a little like crazing in porcelain glaze.  

Keep slabs damp and covered for several days to slow the cure, harden the surface and gain the maximum benefit from the cement.

Slab floor Phase One

Second and third weeks of May '09 Slab floors Phase One

Abe and Terra stripped the formwork from the footings and made a site clean-up.  Luke hauled in a split load of gravel and sand for underslab prep.  

We started with two inches of gravel so we had a bedding for the electrical conduits, then we made connections to the stubs from the footing so we had complete circuits for each of the wall systems, and brought the gravel up to three inches below top of footing.

We laid a one-inch styrofoam insulation barrier on top of 6 mil visqueen, then ran the plumbing lines from the water heater closet to the kitchen sink and for the radiant slab.

With the plumbing in and insulated, we laid two inches of sand, up to the top of the footing. 

Slab reinforcing was 3#'s at 12" each way, set on 1-1/2" dobes.  For the radiant slab we used zip ties to secure 1/2" Pex tubing to the reinforcing on a 12" spacing; one zone for each of the two rooms.

I'm going to let Taj tell you about our special sand, gravel, cement, and red clay formulation for the slab in the next post.

North two footings

First week of May '09:  Footings for The North Wing

After a half day of digging, we jumped into that massive hole and quickly set the perimeter form:  2 x 12's hung on steel stakes driven to a string line pulled off the foundation line.  We dropped the #5's into the trench and while Khyber and Abe set the inside form, Terra, Taj and I tied the grid:  #5's at 12" each way.  The whole thing took about eight hours for each of the two modules.

Once the formwork was up, we needed to identify the center line for all of the walls, and since the center jumped around the cut outs for closets, this was a little tedious.  We set 2x4's across the footing as end wall markers, then longer 2x4's on top for both center line markers and as attachment points for the vertical steel dowels that would tie the walls to the footings.

We also had to run the electrical conduits that would service each of the rooms from the sub panel.

We had an inspection from the county, then were ready for the pour.  We ordered a 4-1/2 sack, cement and fly ash blend, with trucks spaced thirty minutes apart.  Each of the footings took 26 yards.  Pouring was easy since we had truck access on three sides.  Terra and Abe stripped the forms the next day, but we made sure to keep it wet for a week to cure the concrete slowly and get the maximum benefit from the cement.

Into the Earth

Spring '09 Into the earth

Finally, after a year of pre-construction activities which included permits, grading, logging, milling, and some distraction to other projects, we started building Terra's House.   The architectural concept which you saw in an earlier post is three rammed earth modules supporting a SIP roof system.  The layout of these separate buildings allowed for a phased construction which would give us much easier site access.  

We marked out footings for the two north side modules, leaving the south side of the building pad for storage of wall building materials as well as equipment staging.  The footings themselves are five-feet across, designed to support the extra wide walls as cantilevered rather than pinned with a roof diaphragm.  The downside to a cantilevered wall design is the extra concrete that has to go into the footings.  The upside is that you can eliminate excessive bolting and nailing in the roof plus you get the soil from the footing to use in the formulation for the wall construction.  It took Luke Noble about four hours to dig the footings for the two modules in phase one and we accumulated nearly forty yards of soil.

The photos in this post show the lay out for the footings, the footings dug, and Terra taking a sample from the stockpile of beautiful red clay we'll use as our primary component in the walls.

Working with Friends and Neighbors

A word from Terra on thinking and acting locally:  As a project coordinator for a community-based nonprofit I have the opportunity to witness on a regular basis, the benefits that arise from friends and neighbors working together.  One of our goals with this house is to utilize local resources and businesses whenever possible.  

In the early stages, we have already had the chance to put this into action.  Noble & Sons, a family business from just down the road, has done most of our site preparation, made us a new driveway, and is also providing our sand and gravel for the walls.   Concrete for the footing and the slab came from a local ready-mix company, we are buying as many materials as we can from the neighborhood hardware store, and custom metal fabrication for the equipment is contracted to ShadowWorx, our cousin, who is also our neighbor.   

In addition to minimizing environmental impact by reducing trucking miles and fuel use, contracting with these local businesses recycles income in our community and the foothills.  On top of that, working with friends and neighbors builds relationships that will last long after the house is finished.  I am already looking forward to having everyone over for dinner under our new roof next year!

Our Home-made Beams

Terra here- I was just out on the site looking at our big stack of home-made beams.  One of the advantages of living up here in the foothills is our access to natural resources in our own backyard.  In addition to our rich red clay, the north slope of our property is covered in a thick conifer forest.  

Last summer, we selected two large Douglas Fir trees and Khyber harvested them with a used Stihl 090.  After they seasoned through the fall, Abe milled them into beams using the 090 and an Alaskan mill, in the same fashion my Dad milled wood 30 years ago for the rammed earth houses we grew up in.  It was a big job, but we had friends stopping by every week to watch the process and lend a hand.