Natural Building on Any House: a Bamboo, Lime, and Earth Addition to a Cinder Block Home

My preparations for a week of travel to renew my 3-month visa here in Guatemala signify the three-month progress mark on the current bamboo-framed building project, and a perfect time for reflection. When I arrived here on December 1st, I was just in time to cut through existing block walls with a 7″ diamond blade, hammer out the spaces for new foundations with a sharpened railroad spike, and mix my first ever batch of concrete. Now, late-February, as I prepare for five days’ absence, I’m sad to be missing some of the plaster and roofing work. A lot has happened in between.

The project we are currently working on is a second story addition onto an existing cinder block house for a couple that works for a local community health NGO. Last year, in Tzununa, the hotel project that I worked on needed four full months of bamboo framing. But on this build, four months is all it will take to complete the whole project.

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The Tzununa Bamboo Hotel

Our first truckload of bamboo arrived the second week of December, and by that time we had finished all the demolition work. We bolted the metal strapping for the guadua bamboo columns into the existing block structure, then embedded it into new concrete foundations. Just after New Year’s, primary framing was complete and we were fitting only small beams and braces.

Julio setting up his work station for the morning.  Also notice the metal strapping ready to accept the next round of bamboo columns in the bottom-right corner of this picture.
Julio setting up his work station for the morning. Also notice the metal strapping, ready to accept the next round of bamboo columns, in the bottom-right corner of this picture.
A cluster of fish-mouth joins, placed to conform to the corners of the existing concrete structure below.
A cluster of fish-mouth joins, placed to conform to the corners of the existing concrete structure below.
Jeremias and Josue using the large hole-saw  to prepare a fish-mouth join.
Jeremias and Josue using the large hole-saw to prepare a fish-mouth join.
Jerman using the grinder to create as perfect a join as possible for a column.
Jerman using the grinder to create as perfect a join as possible for a column.

I credit this not only to the smaller size of the construction, but to the team we have on site. At the medical clinic in San Pablo, the team was an excellent group of stone and concrete workers, carpenters, bambuseros, and earthen builders. While building the hotel in Tzununa, I learned and practiced the art of cutting and fitting bamboo joinery with a team that was also fairly new to the trade. Now, here in San Marcos, we have combined the best of each of these teams into a crew of 12 extremely efficient workers. With their increased confidence and proficiency in bamboo construction, it has been both amazing to see the speed of progress as well as challenging to keep up with their work pace after my few months away from construction.

Am interesting corner join, where a primary beam is fit to both a beam and a column.
Am interesting corner join, where a primary beam is fit to both a beam and a column.

After the framing was done, it was time to add a roof and walls. As one part of the crew worked on fitting the long bamboo rafters, composite cypress roof beams, and braced bamboo trusses, another was starting on a modernized version of the classic Guatemalan bajareque wall. Instead of cane or small bamboo tied to posts with rope made from sisal agave fibers, we were fitting 1×2 pieces of pine to each column, bracing them at 45-degree angles with 2×2 pine, further bracing the diagonals to the bamboo beams with more 1×2 pine, and then fitting thin wooden lath across the span of the wall with a nail gun. The result is an extremely strong wall with all of the bracing embodied inside of it. Here on Lake Atitlan and at Return to the Forest, it has to be both earthquake-proof AND beautiful!

Bamboo rafters being fitted to a braced bamboo roof truss.
Bamboo rafters being fitted to a braced bamboo roof truss.
The rafters are measured and leveled, then cut at the exact angle to which we will be fitting the wooden ceiling panels.
The rafters are measured and leveled, then cut at the exact angle to which we will be fitting the wooden ceiling panels.
This composite beam is fitted through a bamboo column, then shaped to the corner formed by the beams behind it using a jig saw and a special grinder wheel.
This composite beam is fitted through a bamboo column, then shaped to the corner formed by the beams behind it using a jig saw and a special grinder wheel.
Seen from below, the rafters for the corner of the hip roof are fitted to the composite beam using 2x4's, fastened to the beam and then shaped individually to each piece of bamboo.
Seen from below, the rafters for the corner of the hip roof are fitted to the composite beam using 2×4’s, fastened to the beam and then shaped individually to each piece of bamboo.
The interior our wall system, complete with a 45 degree brace, upright braces attached to the 45 brace and the beams, and all of it's wooden slats installed.
The interior our wall system, complete with a 45 degree brace, upright braces attached to the 45 brace and the beams, and all of it’s wooden slats installed.
The house, with the original 1st floor slightly visible, in varying stages or wall and roof progress.
The house, with the original 1st floor slightly visible, in varying stages of wall and roof progress.

For the fill, the traditional rocks and mud are replaced with a mix of lime and pumice sand, which is widely available here in Guatemala due to its high volcanic activity. This part can get a bit tedious, but the more thoroughly the walls are filled, the better the first layer of plaster sticks, so it is important to take great care and leave no gaps. The living room will have some sections of adobe brick walls, built only up to a huge window overlooking the garden. This is giving some of our volunteers their first opportunity at working with mud in a structural capacity.

A view of the first two stages of the walls for this build.  The corner of the two wall sections toward the right of the picture dislpays the gravel and lime fill, and the smoother-looking walls in the middle and left side of the picture display the base layer of lime plaster.
A view of the first two stages of the walls for this build. The corner of the two wall sections toward the right of the picture dislpays the gravel and lime fill, and the smoother-looking walls in the middle and left side of the picture display the base layer of lime plaster.
Adobe bricks for the living room being prepared and laid out to dry by Jeremias.
Adobe bricks for the living room being prepared and laid out to dry by Jeremias.

As we advanced on filling the walls, another part of the crew worked on fitting the routed tongue and groove ceiling panels. The result is an attractive wooden ceiling, coated with linseed oil for protection, above exposed bamboo rafters and beams. In our bamboo constructions, we always leave the rafters exposed to the inside so that you can admire their natural beauty. The final roofing material will be corrugated metal lamina, as it is more waterproof and will last longer, all at a lower price and weight than the other options for roofing available to us. Surprisingly enough, this mix of natural and not-so-naturual building materials is becoming more popular with some of my building design teachers in the United States as well. In the U.S., the standard roof on a beautiful timber frame, straw bale and earthen house can often be standing-seam metal for water drainage and durability. Lamina is the cheap, available option for Guatemala.

The roof truss, exposed rafters, and ceiling panels in the living room.
The roof truss, exposed rafters, and ceiling panels in the office room.
The same composite beam as pictured above, but with the first layer of lime plaster completed, the ceiling panels installed, and all of the rafters fastened into place.
The same composite beam as pictured above, but with the first layer of lime plaster completed, the ceiling panels installed, and all of the rafters fastened into place.

Over the past week, we have moved from the rough mix of wall fill to the first layer of plaster. This is constituted of lime mixed with medium-coarse sand and a bit more water. This was my first time learning to plaster, so it was interesting to learn that the experienced masons’ technique of whipping the plaster at the wall with a metal spatula actually takes quite a bit of finesse and concentration. The final result, however, is miles more satisfying than just filling the walls to the top. If you do a bad job, it is instantly noticeable that the wall is uneven. However, if you are thorough, the result can be quite beautiful, even with just the primary lime mixture. We are also working on creating a relieved edge with this layer of plaster, both for aesthetics and to prevent separation between the bamboo and the plaster as it dries. These walls will be finished with a fine earthen plaster, giving the interior of the house a warm clay color and a smooth look. The final result will resemble a pillow, or cloud, of earth in between lengths of bamboo.

A wall section with the first layer of plaster completed.  Note the relieved edges where the wall meets the bamboo beams and columns.
A wall section with the first layer of plaster completed. Note the relieved edges where the wall meets the bamboo beams and columns.
A primary application of the earthen plaster mix, to be smooth out and coated with nopal (prickly pear) cactus sap.
A primary application of the earthen plaster mix, to be smoothed out and coated with nopal (prickly pear) cactus sap.
The adobe wall in the living room, above which will be installed big, sliding glass windows.
The adobe wall in the living room, above which will be installed big, sliding glass windows.

I know that when I come back in a week, I will see yet more progress, and the building will likely have most of its walls finished and a roof installed. I’m hoping to still catch a bit of earthen plastering next month, as well as fired clay flooring. This project has been an amazing learning experience, as Vicente, the head albanil, does an incredible job of balancing a hard work ethic with teaching and the sharing of construction knowledge. Working for Charlie, with the right attitude, can provide an unparalleled experience of a classroom where you earn your lessons through sweat and sore muscles, all while sharing laughter and tortillas. Stay tuned for an update on the next months of finish work!

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