My inspiration for zipper stairs came from a visit to Mesa Verde National Park, where the Anasazi Indians had carved hand and foot holes in the rocks to climb up to their cliff dwellings. Their holes were small, and were probably chipped out with much difficulty using crude tools. If one were to expand the holes until they touched each other, something they did not do, the end result would be similar to zipper stairs.
Stairs are used to climb an inclined plane. They have a vertical face and a horizontal face. As the inclined plane gets steeper, the vertical face gets higher and the horizontal face gets narrower. The higher the step, the harder it is on ones knees. As the horizontal face gets narrower, ones foot eventually doesnt fit on the step, unless the foot is placed sideways, which is awkward. Going up and down traditional steps becomes more dangerous the steeper they get.
Using zipper stairs on the same slope, there are more steps, so the vertical rise for each one is shorter and more comfortable for ones knees. Also, by turning the steps at an angle to each other, one gets the diagonal distance of the rectangle for ones foot, which is longer than the short distance provided by normal stairs. Zipper stairs are more comfortable and safer for steep slopes than are traditional stairs.
This instructable will show some of the zipper stairs I have made over the years and follow one stairway project from beginning to end.
Step 1: The Project Begins
The slope is steep, a perfect place to use zipper stairs.
After the stairs are carved into the dirt, and the ravine is filled, everything will be covered by a layer of nylon-cement. Nylon-cement is a combination of nylon fishnet and cement, a material I developed many years ago, and have built my whole house out of. You can see one project I have done with it on my road repair instructable, https://www.instructables.com/id/ROAD-REPAIR-with-NYLON-CEMENT/
Think of nylon-cement as you would a layer of fiberglass. The fishnet replaces the glass cloth, and the cement replaces the resin.
Step 2: The Inclined Plane
With traditional stairs, as the slope increases, each step becomes more difficult. Higher steps are harder to make for people with weak knees and hips. Traditional stairs also have narrow steps on steep slopes, with no way but sideways to place your foot.
With zipper stairs there tend to be more steps that work into the pattern, and each step has a lower and more comfortable height. Since sipper stairs are set at an angle there is more distance on each step for one to place the foot.
I think that zipper stairs are probably safer for small children to climb up and down than are traditional stairs. With traditional stairs, a body starts rolling and keeps rolling to the bottom. With zipper stairs, a child would tend to bounce from side to side, and soon come to a stop.
On lower slopes, there is nothing wrong with traditional stairs. As the slope increases, however, the traditional stairs should morf into zipper stairs. Zipper stairs are not always at 90 degree angles to one another. There is an angle to fit just about any situation.
Step 3: Carving the Steps
The basic tools I used to carve the hillside were a hoe and a machete. I am fortunate to not have granite here, as far as carving goes. We have a lot of clay, and a semi-hard rock called "tosca", which is like hard clay.
I started at the top. From above, you can look down and imagine at what depth the next step will be. A long-handled hoe will let you stand where you are and carve out the step below it. Then you can stand on the new step and carve out the following one. It is fairly safe to carve on a slope this way, and most of the excavation dirt slides down the inclined plane to the bottom.
After roughing out the design, you can tweak it with the machete, sharpening up the edges of the steps for example.
Step 4: Splatter Coat
I usually do this step in the late afternoon, so the cement has the cool and moist night time for hardening up well. If cement dries out before it cures, it hardens up less. Thin layers dry out faster, so I prefer to work after the heat of the day.
When doing the splatter coat, wear old clothes, eye protection glasses, and a hat if you get really messy. Doing the stairs, it was mostly my feet and lower legs that got splattered.
Mix a bucket of water and cement, without sand, and stir it up. You get a slurry that we call "lechada." The mix consistency is like watery paint. Use a big brush, the kind cement workers use, to fling the lechada.
To test the consistency, fling some on the ground. If you can see the color of the ground showing through, the mix is too thin. Add more cement. If the mix becomes too thick, it becomes harder to fling. Anything more than the minimum needed to cover the earth is probably wasting cement.
The splatter coat usually hardens up enough overnight that by the next afternoon one can walk on it and continue with the next step.
Step 5: The First Coat
If it was more convenient to work on the sides of the project, I would normally put down the fishnet and the finish coat right away, while the bottom layer is still fresh. This difficult terrain calls for a two-step process, putting down the first layer and letting it harden so that one can then walk on it to do the net and finish layer. If the first layer of cement stays clean, the second layer should adhere to it well.
Sweep the steps after the cement hardens up a little bit, to knock off any rough spots that might make the following steps more difficult.
Step 6: Laying Down the Fishnet
I made the biggest recycling score of my life when I got my fishnet free as waste from the tuna fishing industry. This is the last of my supply, however, and no more is available locally. New fishnet is not cheap. Some chemist should figure out a way to recycle our waste plastic into a mesh material for plastering.
Step 7: Top Coat
If your cement mix is too thick to penetrate the fishnet and adhere to the bottom coat, water down some of it and rub it in with your gloved hand. Put the thicker mix on top of that and create your final texture. For these stairs, I swept the surface with a broom to create the final texture.
When it hardens up enough to spray with water, try to keep it damp during the heat of the day. You should be able to walk on the project in a day or so.
Step 8: Other Examples of Zipper Stairs - 1
Step 9: Other Examples - 2
As you can see, cracks do form, and weeds do grow in the cracks. A string trimmer takes care of most of the weeding.
People tend to step on the edge of steps, instead of in the middle of the step. The steps tend to get damaged on the front face of them because of that. I make the front faces thicker now when I make steps. Also, tree roots can grow under the thin layer of cement and break the step as the root grows. If roots rot away under the cement, they cause hollow areas, which can cause the nylon-cement to break and sink in under the weight of a person.