Anatomy of a Project (Vol. 5.3) - The Stovetops

Each inkawasi stove has two “stovetops” (I really have no idea what else to call them in English) that are cast out of concrete and internally reinforced with rebar.  In Spanish we call them planchetas de concreto or just planchas.  These are the first things that need to be made when building an inkawasi stove because they have to be already dried and cured when the actual stove is built.  In other words, you have to fabricate them beforehand so they’re ready to go on build day.

As indicated by the inkawasi schematics posted in volume 5.1, the inkawasi stove has two levels and two “burners.”  The design calls for one stovetop (and one burner) per level.  The front stovetop has the main burner located over the combustion chamber (where all of the actual cooking takes place) and the back stovetop has the secondary burner (where you can put food to keep it nice and hot), as well as the chimney.

In order to cast a plancheta you need water, sand, and cement, corrugated and smooth rebar, metal stripping, and wire for tying.  You also need to make a simple wooden mold (called a formaleta in Spanish) and be prepared to solder a bit.

There's some casual soldering gear there on the ground

Many of the tools you'll need to get the job done

To make the burner hole in the stovetop, you bend the metal stripping into a circle shape with the approximate circumference of a standard cooking pot.  Each burner hole uses two of these metal stripping rings stacked on top of each other, with short pieces of corrugated rebar soldered in between them.  This forms what will become the burner of the stovetop.

Don Pedrito checks for squareness

Here you can see how the metal stripping is stacked and soldered

Then you build the latticework structure that reinforces each concrete slab.  This structure has a border made of corrugated rebar and an internal grid made of smooth rebar.  The pieces of rebar are held together with tying wire, and the burner hole made from the metal stripping is placed in the middle.

Some completed latticework structures awaiting concrete

When your latticework structures are all ready and resting comfortably within their wooden molds, it’s time to mix up your concrete.  I believe the most common mix ratio is 1 part cement, 2 parts sand, and water to gusto, but you can play around with it to get your desired consistency.

With the concrete mixed and ready, it’s time to fill in your molds.  There’s a neat little trick for raising the latticework structure so that it lies suspended in the center of the concrete slab and not sitting at the bottom: all you need to do is prop up the lattice with a few small rocks before you pour in the concrete, and the mixture fills in around the rocks (they’re making minimal surface contact with the ground due to their rounded or jagged sides) and they disappear, leaving the lattice suspended magically in the middle of the concrete plancha!  After pouring the concrete into the molds you smooth out the surface with a straight piece of wood.

It’s also important to remember that you’re making two slabs of concrete for each stove and one of them needs to include a hole for the chimney.  We’ve found that a hole about four inches in diameter is perfect for a chimney, regardless of whether you use concrete tubing or metal to make it.  To form the chimney hole when casting the planchas you can use a piece of plastic PVC pipe or anything else that will leave a four-inch diameter hole.

For our project, the biggest challenge in making the stovetops was the logistics.  This project is for seventy stoves and each stove calls for two stovetops, so we had to cast 140 concrete slabs in total.  We ended up making fifteen wooden molds, so one community used seven and the other used eight.  This means that each community could only make seven or eight planchetas per day, since they need about 24 hours to dry and cure enough to be taken out of the mold.  The whole process of fabricating the 140 stovetops took about two weeks to complete.

Next up will be a closer look at the construction of The Table, which is the surface upon which the stove itself is built.  Stay tuned.


    • (Vol. 1) – Intro to Economical Stoves
    • (Vol. 2) – Community Development…The Goal
    • (Vol. 3.1) – The Key Players
           (Vol. 3.2) - The Designers/Facilitators
           (Vol. 3.3) - The Community
    • (Vol. 4) – The Problemática
    • (Vol. 5.1) – The Stove Design
           (Vol. 5.2) - Materials and Design Elements

           (Vol. 5.3) - The Stovetops ***

           (Vol. 5.4) - The Table

           (Vol. 5.5) - The Stove Itself

           (Vol. 5.6) - The Chimney

    • (Vol. 6) – Community Workshops
    • (Vol. 7) – The Budget and Funding
    • (Vol. 8) – Designing for Sustainability