Earthship Construction Update; plaster & plumbing

This post is an attempt to catch up with the technical details of our earthship construction activities of this summer … so bear with me as I will be touching on a number of different areas …

I wrote this post about a month ago but just got around to adding pictures and drawings today … there are many more pictures on our Facebook page.



We recently pulled our plumbing permit (end of July) for this project.  Our approach has always been that we are building a code compliant septic system with the ability to divert the flow (using 3 way diversion valves) from specific plumbing fixtures (sinks, bathtub, shower, laundry) to our grey water system.  The alternative approach would have been to design a grey water based system from scratch requiring input (and cost) from an appropriately code certified individual (engineer or certified waste water tech).  Our plumbing permit is for a standard, BC Building Code compliant septic system that easily allows us to divert the grey water flows.  This allows us to incorporate grey water into our building when the BC Building Code addresses gray water systems at some point in the future.

I have attached a copy of our plumbing permit isometric drawing to the top of this post.  I suspect this drawing is a little difficult to interpret without looking at a plan view of the earthship showing the plumbing fixtures at the same time.  (I have this drawing but still need to track down a jpeg of it … there is a floorplan drawing that may help in the photos section of  the website.)  To implement the grey water part of this system a seperate set of grey water drainage pipes were specified.  In order to remain code compliant all of these grey water pipes ultimately flow into the black water drainage system.  Three way diversion valves (we are using Jandy valves … which seem to be the most common choice for this work) allow for the flow to be sent in one of two directions; either to the septic or grey water system.

Our first implementation stumbling block occured from the use of these valves; the current plumbing code does not address grey water diversion.  As such, we will not be installing these valves initially … for the time being the grey water pipes will flow directly into black water pipes where these valves will eventually go.  This keeps our system code compliant and allows us to finish our grey water system when the BC Building Code is more clear on this topic.  The photo attached to this paragraph shows the grey water line stacked on top of the black water line with a right angle fitting at the end joining these two lines … the right angle fitting will eventually be replaced with a Jandy valve.

One struggle I found implementing this plumbing system was dealing with inconsistencies between tradiitional plumbing and grey water.  In a grey water system the preference seems to be for smaller diameter pipes for better flow (ideally not larger than 2″).  A typical plumbing system uses larger diameter pipes as the various black water flows are combined (typically 3 and 4″ diameter) … again for better flow when dealing with the solids encountered in a black water  flow.  We kept our largest grey water diversion pipe to 3″ (necessary to be code compliant for the septic system).

When we built our front tire wall we installed plumbing sleeves between the tires at the correct height to run the building septic drain line to our septic tank.  Unfortunately, we did not place these sleeves in locations that simplified the plumbing system.  We abandoned these sleeves and chose a new location for our building drain line to exit the building based on our final , submitted plumbing permit.  In order to run this pipe through the front tire wall we had to bore a hole through one of the front wall tires.  We used a sawzall to cut a hole of the desired size through the tire.  We were able to cut the tire; we went through a lot of sawzall blades, and it was a very frustrating job.  The vibration of the sawzall caused a substantial amount of the dirt packed into the tire to vibrate out of the hole that was being cut … after placing a sleeve for the plumbing pipe through the tire we re-packed the void in the tire with concrete.  Moral of the story … think twice and lay plumbing sleeves once!

We laid out all of our grey water and septic lines that will be buried under the floor or run along the walls in the bathrooms.


For the time being we only dealt with supply lines we are installing under the floor.  We ran a number of 3/4″ PEX lines from the utility room to the main bathroom.  To simplify this job we packed these lines into a 4″ diameter PVC conduit and bedded the conduit in screened gravel before burying it under the floor.  Any hot water lines were wrapped in insulation before being placed in the conduit.  The conduit was not strictly necessary; PEX can be directly buried under a slab and sleeved only where it comes through the slab … the conduit under the slab hopefully guarantees we will have no problems with these lines down the road.

Wall Plaster

Note: There are lots of pictures of what we are up to at our Facebook page (I may try and figure out how to link pictures between facebook and our website if we ever slow down … some pictures of wall plaster can be found here).

This spring we did our final tire pack outs … we did a total of about five packouts to get to the point where the walls were kind of smooth (only a little bit of tread from each tire was visible).  This was a slow job as he walls needed to dry after each packout.

We also placed ‘starter’ studs in the utility and kitchen U’s.  These studs are attached to the walls (screwed to the tires), and will act as the end points of the walls seperating the pantry from the kitchen and the utility room from the front of it’s U.  The studs were placed before the base plaster coat so that they could be used as plaster stops.

We were then ready for the base coat of plaster (also referred to as the brown coat or scratch coat).  For this job we decided we wanted some help and got in touch with Cindy Walker.  She lives in the Nelson area and has been working with earthen plasters for over a decade.  This proved to be a good decision … Cindy is very experienced and made what I am guessing would have been a very frustrating test of marital bliss seem quite simple.

The last week of July Sandra organized a plaster party and with Cindy’s help we got all of the U’s plastered. in about 4 1/2 days.  Big thanks to all of the volunteers; lots of help from family, previous volunteers and also met some new people!

Prior to plastering we screened gravel and clay through a 1/4″ screen (about 5 yards of each).  We used most of the gravel and over half of the clay for the back walls (about 1500 sqft of walls).  The mix for the wall plaster was 6 parts gravel, 4 1/4 – 41/2 parts clay, 4 1/2 parts chopped straw, 1/3 cup of borax detergent and water as required to get the desired consistency.

Our clay has a fairly high silt content (clay slip that was mixed with it settled to the bottom of the bucket over the course of a day (apparently this will take a lot longer with less silty clay).  This means that we used a lot more clay (4 1/4 – 4 1/2 parts) than would usually be required (a typical mix is apparently 4 parts gravel to 2 parts clay?).

This is the first time we used straw in a cob mixture, to  this point we have been using sheep’s wool.  I suspect you could make this mix work with wool, but we did not want any problems with our plaster coats and straw is what is typically used for the mixture.  We used 5 square bales of hay chopped through a stationary leaf mulcher we bought online from the Home Depot.  The mulcher is basically a whipper-snipper head mounted upside down in a cone; the straw is dropped into the top, passes through the whipper snipper and chopped straw drops out of the bottom.  We found that with fresh cutting cord installed on the head we got good results (pieces about 1″ in length).  As the cord got shorter with use we had to run the hay through the chopper twice to keep the straw lengths short enough.

The borax is added to prevent the straw from going mouldy as the walls are drying out.

We mixed using two small cement mixers (two to produce enough plaster to keep the people plastering busy).  We mixed the clay and sand together first … adding the materials and enough water to keep it hydrated such that the plaster was not clumping in the bottom of the mixer. After, the borax was added; the borax was added to a cup of water and stirred before being added to a mixer.  Finally, the chopped straw was gradually added.

The final mixture was unifrom and spread easily  If the plaster was too dry the plasterers had to work very hard to smear it onto the walls and trowel it smooth, if it was too wet the plaster would drop off the walls.

The base coat was hand-smeared onto the walls and then troweled smooth using wooden floats.

Our base coat of plaster was about an inch thick … much thicker in places that required more smoothing!  We do not have perfectly smooth walls, they undulate where different tire diameters were used.  A ‘flat’ wall would probbly have required another layer of packout prior to plastering, or more uniform tire diameter selection back when the walls were being built (hindsight is 20/20!).

The walls have taken about 2-3 weeks to dry in fairly hot, dry conditions.  We ran fans in the rooms initially, and left all of the windows and doors open.

Earthen Floor

We are now thinking about the earthen floor.  We hope to get the base layer of the earthen floor done now before winter so that the floor has warm drying weather so that it will dry out quickly.

As currently planned the floor consists of 5 layers.  The first layer consists of 4″ of compacted, granular fill, and is already in place.

The second layer is 15 mm poly lapped 4″ and sealed.  The poly acts as a moisture/vapour barrier, and also as a radon barrier.

The third layer is a cement/perlite mix thick enough to get the minimum R12 insulation layer now required below a slab floor.

The fourth layer will be the base layer of the earthen floor (about 3″ thick).

The fifth and final layer will be the finish coat of the earthen floor (about 3/4″ thick), finished with an oil coat for durability.

Some Thoughts on Green Building Materials

I did spend some time trying to chose green building materials for these jobs … but ultimately found there were no clear winners.  You do not even have to spend a day gluing together ABS pipe to realize that prolonged sniffing of the cement cannot be good for your health.  PVC/ABS/PEX pipe, cement for concrete and rigid insulation are all pretty nasty products to produce and do not break down well in the environment when we are done with them.  I found convincing arguments for using/not using copper/cast iron/plastic in these applications and at the end of the day did not feel great about any of the choices.  I was somewhat constrained by the Building Code in terms of which materials were allowed for a given application.  My ultimate goal was to minimize the plumbing runs, using as little material as possible and also to keep to the smallest diameters possible.


Electrical Rough-In Wiring of Earthship Tire Walls

It has been a few days since we finished our rough-in wiring, but I thought I would post about it before I forget the details.

As mentioned previously we spent some time after getting our electrical permit figuring out what type of wire would be required for the tire walls; the electrical inspector initially wanted us to use metallic or non-metallic conduit to protect against corrosion and moisture.  Based on our research of other buildings of cob construction in British Columbia we were able to show the building inspector that standard wiring and boxes have been used in buildings with similar construction techniques.

Last week we finally started the rough-in wiring of the tire walls.  I started working on the ends of the interior tire walls; we have wire running in channels at the tops of these walls and there will be switch outlets on the ends of all of these walls.  We decided to frame a wiring chase on the end of every wall rather than cob over this wiring.  There were two reasons for this choice; I was worried that there would not be a lot of cob covering the wire runs on the ends of the walls, and we intend to finish these chases so that they look like posts at the ends of the interior walls  … we hope that it will be aesthetically pleasing.  Making these boxes was slow work as the 2×6 forming the box had to be custom fit to the tire stack.  Eventually we will cob over the custom edges of the 2×6 when we finish mudding the walls.

On each of the end walls I put a 3 or 4 gang electrical box approximately 4′ above finished floor height.  These boxes will hold the light switches for the main room lights.  The intention is for all of the lighting circuits to be on DC power.  I ran some of these branch circuits using #10 AWG wire due to the length of the runs and number of lights on the circuit; I did not want any issues with voltage drop due to insufficient wire sizes.  I also placed a single gang box approximately 1′ above finished floor level in these chases.  This allows me to have a DC plugin in every room, something I was not sure how I was going to accomplish otherwise.  I did not include these DC plugins when ensuring that there was no point along the wall of the room further than 12′ from an electrical outlet; I ensured that you are always within 12′ of an AC plugin.

Once these end wall chases were finished we moved on to the wiring beside the east and west exterior doorways.  Here again electrical wiring for room lights travelled in a channel at the top of the tire wall.  This wiring was brought down to approximately 4′ above finished grade into a switch receptacle gang box by running it in the recessed grooves between the tires. The wires were attached to the tires using 3/4″ screws and CSA approved wire clips.  Here again, a single gang plugin was placed underneath the switch box.

Finally, all of the branch circuits were run for the plug receptacles on the tire walls.  All of these gang boxes were mounted on plywood screwed over the cavity between two tires in the wall.  A box was cut out of the plywood using a jigsaw and the gang box was mounted and screwed to the plywood.  Before mounting the gang box 6 mil poly and stucco lathe was stapled over the exposed face of the plywood.  The lathe extends beyond the edges of the plywood.  As described above the electrical wire was stapled in the cavities formed between the tires.

We passed the wire between rooms by drilling through the cob packed between the tires.  This worked well and reduced the wire runs as we did not have to go right out to the end of each wall.  We made sure the wire was stapled within 6″ of entering a gang box and at least every 5′ feet along its length.  At least 6″ of conductor was run into the gang boxes.

All of this work took two of us three days.

The Front Wall … Re-Evaluating our Choices

With the roof mostly done, we have started thinking about finishing the greenhouse wall.

The tire work, bond beam, and basic framing for this wall is already done.  So at the beginning of the week we started to size and order the 1″ insulated, double pane glass units.  We identified two companies in Kamloops that supply sealed glass units, and  we also started framing the support blocks for the glass.

We did not get very far though before concerns about the front face glazing as specified in the Earthship volumes stopped us in our tracks.  I have spent a fair amount of internet time researching earthship construction projects, and the glazing  (a fancy way to say glass) seems to be a fairly common problem spot.  As described by one owner/builder,

WARNING: Michael Reynolds’ mullion design for slanted glass panes (external window ‘clamp’ metal), as presented in “Earthship” Vol. 1, not only leads to leaks into the house but will continually require maintenance, do nothing to alleviate condensation drips, AND they’re ugly.


The possible concerns seems to be twofold; the potential for leaks on the exterior face, and the potential for moisture condensing on the inside face to run down into the wooden framing and the plaster covering the tires.  In all fairness, I have also read people’s posts stating that they do not have issues with water condensation, or that it occurs but it is not a very big deal.  The Earthship volumes do specify using a redwood for this framing (like cedar), which is very rot resistant and handles moisture well.  However, we did not use cedar (we used spruce/pine as this was available to us), and all things being equal we would like to avoid rot and moisture stains on the wood and the front face plaster if we can.

Our solution for this concern seems to be to install an extruded aluminum glazing system onto our 3×8 front face stud wall.  These glazing systems simplify the exterior flashing work, and provide interior gutters to catch condensation drips before they reach the wood framing.  This convenience comes at a price and it looks like the materials for our job will be in the neighborhood of $3500.00 dollars (I am still evaluating potential suppliers).  We plan to install this package ourselves.  This is not an expense we had planned on as the materials specified for this job in Earthship Volume I would probably cost around $500.00 dollars.  However, the cost is not huge, and in the long term we hope it wall pay off!

My bigger concern has been the delay this introduces into the building project.  I can be fairly linear when focused on a task, and I was all set to focus on front face framing OVER THE NEXT TWO WEEKS.  The earliest we can expect to get the glazing system is TWO WEEKS FROM ordering it and we still have not placed an order.  On top of that we will probably not place the glass order until we have installed this system and that means ANOTHER WEEK waiting for the glass.  This means that we will not have our front face exterior finished by end of September earliest, and more likely SOME TIME AT THE BEGINNING OF OCTOBER.  I am getting tense just writing about it … waiting was not part of the plan!

Fortunately, my common sense has come to the rescue.  We have lots of other things to do in the meantime and we can switch our focus to these things.  I just have to remember to take deep, calming breaths occasionally.  Strangely, my common sense looks and acts a lot like Sandra, and has been speaking to me in a loud, irritated voice lately when I talk about my original schedule.

So! Other than thinking about the front face glazing we have started mudding the interior tire walls, framed the west exterior popcan wall, and continued working on the east exterior popcan wall.  Christie (a childhood friend of Sandra’s) and her daughters (Sophie and Maya) helped us with the first packout of mud and cans between the tires in the living room … thanks guys!

We have had a fair bit of rain over the last couple of days and the good news is that there are no leaks in the roof (other than the unfinished skylights)!  The water drains really well off of the roof along the three canals that we placed at the back of the roof.  Unfortunately, the concentrated flow of water from the canals is causing some erosion at the back of the berm.  The canals simply stop at the edge of the berm as we have not installed cisterns, and we need to do something temporary to further direct this water.  We will probably do something before too long …