Making and applying an earthen plaster exterior finish

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ziggy
on November 19, 2008
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Welcome! I hope you'll follow along as I continue to build my first cob house. Please consider subscribing to my RSS feed. Thanks for visiting!

A week or so ago, while the weather was still reasonably comfortable, I decided to experiment with making an earthen finish plaster. I settled on ingredients and a recipe for my earthen plaster mix relatively easily after talking to others who have done plastering here at Dancing Rabbit in the past.

Earthen finish plaster recipe

My recipe is as follows:

  1. 3 (five gallon) buckets of sifted sand (sand sifted through a 1/8″ screen to remove pebbles)
  2. 1 bucket of mixed wet clay
  3. 3/4 bucket fresh cow manure
  4. cattail fluff (to taste - enough until I could see the fibers in every handful of material)
  5. 8 cups of wheat paste

Applying the earthen plaster

This recipe proved to be a pretty good starting point. It was a very wet, sticky, and fibrous mix that held easily to the (soaked) wall. I applied it by hand to a portion of the exterior wall, and waited for it to dry. Thankfully, the plaster did not freeze at any point, and it seems to have dried relatively easily (despite cold temperatures) and thoroughly with little cracking. The coat is quite thin - straw from the cob wall can be seen poking through most of the wall, but I think I like how it looks.

After the plaster had some time to dry (but before it dried completely), I used a piece of EPDM rubber (just some extra cut off from my pond liner) to burnish the plaster, making the surface even smoother. The results were pretty pleasing.

The left photo is an unplastered wall, and right is a plastered and burnished section of wall. (Click for larger versions.)

earthen plaster - before earthen plaster - after

As of now, the entire eastern and northern sides of the house are plastered with just a single batch of earthen plaster. I will not do any additional plaster work until the spring, once it warms up again.

For some background information on earthen plaster, please check out my latest entry on Green Building Elements: Natural Building 101: How to Make and Apply Earthen Plaster Finishes

Still here, but almost done for the year

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ziggy
on November 18, 2008
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When all of your energy comes from the sun, and the sun don’t shine for a week, that means there ain’t no power to keep this blog updated.

So. Anyway. Building is definitely winding down and pretty much done for the season. I will put up a few more entries detailing the last of my cob building exploits for the year, and then I will slowly enter hibernation mode.

I would like to keep this blog rolling in the off season, so I am considering creative ways of keeping relevant and fresh content coming even while I’m not working on my house. We shall see.

Nevertheless, expect a little bit about my earthen plastering experience and winterproofing the house in the near future.

How to build an earthen floor

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ziggy
on November 7, 2008
in Earthen floor and Resources
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Recently, I wrote an article about building earthen floors for Green Building Elements. Earthen floors are commonplace in straw bale and cob buildings, but they can also be installed in more typical suburban homes.

Check out the full article here: Natural Building 101: How to build an earthen or adobe floor.

Starting to build the earthen mass floor

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ziggy
on November 3, 2008
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When I began building, I decided to leave the topsoil in my house instead of hauling it out. I guess mostly to avoid the extra labor, really.

floor-dirt

Over the months, it has become quite tamped and solid from continually walking on it. I decided to leave it as is, with the original slope of the land, supposing that any moisture that does happen to get in there (which it shouldn’t) will run out towards the drainage trench.

Moving and tamping the gravel

Next up was moving gravel into the space. I estimate it took about six tons of material. The gravel is about 3-4″ thick on the east side, and 12″ on the west. (It is 1″ clean gravel, for the record.) It was surprisingly easy to level - I hardly had to do anything other than rake it and eye it to judge it level. Although having level dots painted on the foundation certainly helped when moving the gravel into the house.

Anyway, next came the tamping. Thankfully, we got the gravel in the house just in time for our annual traveling Halloween party. Typically, we celebrate Halloween by traveling around the village, making stops at different (and predetermined) houses and locations. Each host has a different activity or snacks or what-have-you. For my stop, we had a GOBCOBATRON DISCO. Presumably, with all of those bodies dancing, the gravel would be tamped more easily than having to do it by hand by myself.

tamp-party

It certainly didn’t do any harm!

Making the earthen floor mix

Now it was time to make the mix for the base layer of the earthen floor: a combination of sand, clay, and straw (surprise!). For this base layer, the ratio of sand to clay that I am using is 3:1, with long straw by the handful. The next (and final) layer will have sifted sand, sieved clay, and chopped straw.

floor-earth

My base layer is 2.5″ thick. Today, I stomped a whole 11 batches of material for the house. There are 14 batches currently in the space. It will need a few more before it is done.

floor-pound

To make the actual floor, I load the (very dry) mix into buckets, and then dump it on the floor. Next I use my hands to knead the surface and make it roughly level. I slap it some with my hands, and then stamp it by jumping on a longish 2×6 board. Stamping it is very tiring and hard on the back. Thankfully, it has been surprisingly easy to keep level. I am not being too picky about having a perfectly level floor, though. This layer is much rougher than the final coat of earth, too, so I’ll be more careful with that final layer.

Getting in the last building work before winter

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ziggy
on November 3, 2008
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I will be headed out of Dancing Rabbit in three short weeks to go back to New Jersey for the holidays. Within the past couple of weeks, I have accepted the fact that I will not absolutely “finish” the house before that time. By “finish”, I mean complete the roof, finish the floor, make my rocket stove and cob bed and bench, and plaster the interior.

So. I’ve done some prioritizing. Now that the cob walls are complete, and the windows and door are in, the house is sealed. My biggest remaining priority is the roof - I need to construct an edge board around the roof, create a soil-retaining system, and have soil moved to my site and load it onto the roof. Oh, and seed the soil, too. That’s not a small load of work by any means!

While I am waiting on a delivery of lumber to build my edge board, I have begun (and finished) some scratch plastering. A few days ago, I moved several tons of gravel into the building in preparation for the earthen floor, and raked it level and tamped it with Kyle’s help. (I estimate it was about six tons, all of which was moved within a 24 hour period.)

The chances are pretty decent that I will be able to finish the floor and the roof. If I do these two things, I will feel confident about moving in for the winter. I am pretty opposed to moving into an unfinished house - especially one without a floor. It would be quite a hassle to work on the house when springtime came (and springtime rains) with all of my stuff in the house and nowhere to store it. However, if at least the floor is done, it won’t be quite as difficult to work on the stove and cob bed and plaster with things in the space.

The weather has been phenomenal lately, which has definitely contributed to quick progress on things. There’s at least a few more days of warm weather in the forecast, too, which is promising.

Three weeks to go! Let’s see what can get done.

Late October cob building photo update

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on November 2, 2008
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Here are some photos from the past couple of weeks:


Finishing the cob walls - it was very tight having to work so closely to the roof.


Installing windows - all of the windows I purchased were some kind of replacement windows - they all had a vinyl exterior trim which we screwed into the window frames.


…and to cover up that vinyl border, I simply covered it with cob.


Here is my dad showing off the free sheep’s wool that I used to insulate around the windows and door.


Moving the door into position - this was an old door that I got from Skyhouse for free - it’s quite heavy, but no glass, unfortunately.


With the completion of the walls, and installation of the windows and door, the space feels much more like an actual house!


The day I almost lose my EPDM membrane - what a mess! Too bad it’s hard to tell just how windy it really was with this photo.


Weaving a giant web with a very useful spool of rope.


With the addition of some scratch plaster, the walls look much smoother and more finished.


Unintentionally scary ghost-face shelves.

Cob walls complete, windows and door installed, and more!

Published
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ziggy
on October 30, 2008
in Cob walls, Earthen floor, Living roof and Plaster
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The past week or so has been quite eventful. There’s been mostly positive progress, but some negative, too.

Cobbing complete!

With Karen’s and my dad’s help, I completed cobbing. The walls are finally done! In just a few days, the gap between the walls and the roof was closed. It was very satisfying to see the final line of the wall meet the decking of the roof. It was awkward work having to stuff the small spaces, but it wasn’t too bad…

Windows and door installation

Next came the windows and the door. My dad and I struggled with installing the first of three windows, continuing our typically discombobulated history of collaborating on work projects. After a couple of hours, we got it in, and the next two were much easier. The north and west windows are casement style, and the southeast is double hung. All are doubled paned.

The door was surprisingly easy to install. A few shims here and there and it was set. Unfortunately, however, it’s not quite what I expected. Meaning that I must have looked at the door wrong when I first found it, and it doesn’t actually open the way I expected it would. It opens outwards instead of inwards. For now, I’m not locking it in cob, just in case I decide to change the door later (or even make my own door). It keeps the cold out, which is good enough for now.

I used sheep’s wool to insulate around the window and door frames where there are air gaps. The wool was free from a local farm, and I simply carded it using my hands before stuffing it in the gaps. The house is now sealed!

Losing my EPDM membrane…. almost

Beyond all that… the biggest happening of the week was almost losing my EPDM membrane on a very windy day this most recent weekend. What a nightmare. All day Sunday, there were gusts of wind up to 45 mph. Since the pond liner was not tied down or weighted in any significant way, it was flapping pretty heavily throughout the day. At one point, my dad ran to find me and said “your roof is about to blow away”, and we made it out there just after the ropes around the tractor tire flew off, essentially freeing the membrane from the roof completely.

We held onto the corners for dear life, and then Jeff ran to find help. Soon a pack of ten or more people were running towards the house, and each grabbed a corner of the membrane, some getting smacked in the face by the EPDM in the wicked wind. Tony and I scaled the house carrying rope, and working like spiders, we all wove a giant web over the membrane. It was a pretty intense experience. People were being lifted off the ground as they held onto the membrane, and up on the roof it was no better. Every time there was a giant gust, the membrane lifted us up off the surface, and there was little to hold onto. Frightening.

Eventually we got the whole roof tied down. Unfortunately, I think the membrane suffered a bit in the process, and there is some damage and wear. Hopefully the parts that are damaged are close enough to the edge that will get trimmed. I also lost some cardboard cushioning that will have to be replaced, so it’s going to take a fair amount of work to get that material back under the EPDM and prepare for the next step in constructing the roof.

Scratch plastering

In the meantime, I’ve been doing some scratch plaster inside the house with the help of my new (and probably last) work exchanger, Kyle. We smoothed out the nooks and shelves, and some of the rougher parts of the wall that experienced some rain damage. It’s amazing how much more pleasing/smooth it looks now, even before the final coat of plaster is on.

Prepping for the earthen floor

Today, Kyle and I cleaned out the house and raked up loose cob and some grass to prepare for moving gravel inside. I decided to leave the topsoil in my building. I didn’t level it either, figuring that if any moisture did get in there, it would drain more easily with the natural slope. The soil has been well tamped by now, after walking on the ground all season, and mixing cob in there as well.

We moved gravel in by wheelbarrow. Because of the slope of the site, the gravel will be 4″ deep on the east, and up to 12″ deep on the west. Above this gravel will be 5″ total inches of earthen floor mix (divided between two layers).

I expect we’ll finish the gravel moving tomorrow, just in time for our traveling Halloween party. I plan on having a gravel-tamping dance party during at my stop. Many feet make work light!

Pictures coming soon!

Dressing up the reciprocal roof

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ziggy
on October 19, 2008
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muslin-under

Before the EPDM went on the roof, I wanted to add a cushion of cardboard on top of the rafters and decking to protect the membrane. And before the cardboard went on, I wanted to add some kind of fabric so that the cardboard would not be visible from inside of the space. I bought a 50 yard bolt of muslin for $50 at Zimmerman’s, and Karen (my current work exchanger) and I draped the fabric and stapled it to the decking.

muslin-dress

Next went the cardboard. This was pretty tricky since the cardboard was so slippery and could not be easily traversed while affixing it to the decking. I used some short nails to try to help it stay in place, which I wasn’t totally thrilled about having to do, since I wanted to minimize pointy things immediately underneath the EPDM. But it wouldn’t really stay in place otherwise.

cardboard-dress

With the addition of the tractor tire and cardboard, the house was looking rather…. interesting…

cardboard-roof

Next came the impermeable membrane: the 35′x35′ sheet of EPDM, weighing in at 380 pounds. With the help of at least a dozen or more other people, we unraveled the EPDM from its roll, and hoisted it up on the middle of the roof. From there, we unfolded it and spread it across the surface of the roof.

pondliner-lift1

pondliner-lift

Without that many hands, the lifting of the membrane would have been an incredible chore…. perhaps even impossible…

I am incredibly relieved to now have the EPDM sitting on the roof. This means I will never again have to get out of bed at 3:00 AM to check to see if the tarps are still covering the roof during a thunderstorm.

Next up: trimming the membrane, making eaves and finishing the skylight, and then lifting lots and lots of soil for the living roof…

pondliner-cover

Making a tractor tire skylight frame

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on October 19, 2008
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tire-lift

A few nights ago, a flash of brilliance struck during a conversation after dinner about making a frame for a future skylight in my reciprocal roof. We were sitting around, thinking of alternatives to making a wood frame, which would have proved quite difficult considering the irregular nature (14 uneven round poles) of the top of the roof.

And then someone mentioned a tire. And then I remembered the huge tractor tires we have lying around on the property, and amazingly enough, the dimensions were nearly perfect: a five foot diameter tire with a three foot diameter hole, perfect for the 4.5 foot diameter rafter ring, and 3.5 foot diameter hole in the roof.

tire

tire-cut

I borrowed a reciprocating saw and cut the tire in half (not a pleasant experience: it stunk [literally]!), and then with the help of a few others, we hoisted it onto the roof, and onto the top of the rafters. Viola! A tractor tire skylight frame!

tirecrown

I plan on having a piece of thick glass cut to the size of the tire, and then I will caulk it to the surface, and then maybe brace it with some screws.

If this works, I will have to recommend it to others with spare tractor tires lying around… of which there are plenty headed for landfills, too, no doubt…

Roof decking complete

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ziggy
on October 14, 2008
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I finished decking my reciprocal roof yesterday. I’m pretty satisfied with how it turned out. It got a little funky trying to nail dimensional lumber up and around some of the knots of wood on the rafters, but overall, it wasn’t nearly as difficult as I thought it might be. It was more time-consuming than anything.

reciprocal roof decking

Next up: making a frame for the skylight in the middle of the roof. This will be interesting…