Urban Forest Cob Experiment, part V: brick and mortar foundation of mismatched chunks


In addition to starting on the cob foundation this week, we happily relocated paintings of friends and family since we’re preparing the larger side of our home for our new tenants.



Hi, how are you?
This welcoming painting by Laura Azar seems to say:  Hi, how are you? so we placed it in viewing of the entrance
Fantastic painting by Bonnie of early Beloved Binge; classic beauty by Rob's ma Sue Tabor and a long-time favorite
Fantastic painting by Bonnie of early Beloved Binge on the left; much-loved classic curved man by Rob’s ma Sue Tabor…a long-time favorite
"Curvist chess" by our talented bud David Glick; each staring produces new information
“Curvist chess” by our talented bud David Glick; each staring produces new information (see the man with the cigarette?)

I also relocated some of our front-yard garden to a new back-yard space near the cob.

Old bookshelf garden: peppers, tomatoes, kale, collards, garlic, and mint to the side
Old bookshelf garden: peppers, tomatoes, basil, kale + collards seeds, garlic, and mint to the side


Building a brick and mortar foundation for cob house

It’s not easy being a bricklayer.  I’m not a bricklayer.  But after a couple of days of mortaring brick chunks together, brick walls convey increased significance in their heavy and considerable labor and precision.  To complicate the process, I’m not using standard brick in most cases, but recycled bricks from an old retaining wall.  These bricks are chunked together unevenly in many different shapes and sizes.  The island of misfit brick.

Learning how to mix and then use mortar
Learning how to mix and then use mortar

As mentioned in my last update, many people dry-stack stone for cob foundations, or use soil-cement to minimize environmental damage. I’m using a pretty sparse 4:1 ratio (4 sand, 1 cement) to minimize cement use.  I increased the cement slightly to 3:1 by the second day to ensure a good hold. I might go back to 4:1 if I don’t notice a difference.


On the first day, I had an experienced instructor/helper named Rob.

Cob, Rob
Patience is good for bricklaying but temper increases tamper

Though I waded through about 10 videos on mortaring the night before, without his expertise, I would have had less confidence and I’m sure I would have made more mistakes.

I skipped a day since it’s quite labor intensive and I wanted my back (and hands) to recover.  Then, I was on my own for the second day of mortaring.  I thickened the wall to 15″, and continued mortaring on the South side of the building.


After 3 pm, a fan is handy to blow away mosquitoes, who don’t mind that I’m wearing long sleeves and jeans and are undeterred at that hour.


I was happy with the progress, but also now realize that the foundation may take longer than expected at this rate.  I’m estimating two more weeks at least.  And a whole lot more sand.

About 15 hours of work
About 15 hours of work

The edges of the wall are each curved inward so the cob does not slip off toward the outside edges.

After mixing a batch of mortar (I’ve mixed about 10 batches) each brick is carefully selected and puzzled into the other bricks (with fresh mortar) while trying not to disturb them (they’re sensitive).  Then, after being tamped in, the mortar squeezes out and must be reapplied around the edges. Curse. Then repeat.

We built one section at a time, careful to measure continually making sure it was around the recommended 15″ wide and knee-height.  The height will ensure water splash on the cob is minimized. The width is necessary to hold about a 9-foot tall cob wall.

I also sawed a pipe Rob had lying around to 16″, then added below the foundation, so that we can run wire and water lines potentially someday.  (Planning on solar power for now.)

Recycled access pipe cut to 16"
Recycled access pipe sawed to 16″

I also used bits of urbanite for some of the wall, which worked nicely when I needed a flat piece of material.

Don’t forget to take breaks

Lunch time is even more rewarding after hard labor. This last mortaring day, I put quinoa in a pot at 10:30 am and, just when it started to boil, turned it off, threw in a bouillon cube, and covered it. By 1:30 pm, it was fluffy and ready for eating. One minute quinoa!  I also had Gardein “fish” sticks (found at Target in freezer section) and steamed broccoli followed by watermelon.

Syba likes to hang out on the pallet deck too during the break, after finishing her dog treat in the Kong.  Here she awaits her watermelon husk patiently.

My Kong bone paw rest
My Kong paw rest


Happy knee cob floor preparation

In addition to mortaring, I spent some time digging away the topsoil to prepare the floor.  It’s recommended that the topsoil be dug up prior to building so the ground is naturally tamped down by all the stomping of the workers.  As I dug, I found a few red ant holes teeming with ants and carefully relocated them as best I could. [Insert video of me screaming and flinging dirt in random directions].

The final floor should be about 2-3″ above outside ground level to avoid flooding.  I measured from the highest point of the ground on the South side and saw that we need to build about 9″ above the current ground! We put a stake in, marked with the final level, for reference.

Floor level: 9" higher!
Floor level: 9″ higher!

It was later removed (without authorization!) but will be returned soon.

The final floor will be built on top of the subsoil, and consist of a layer of drainage rock (about 4″ – plenty of QT with the wheelbarrow), possibly a clay/straw mixture, then two layers of cob.

In the final layer of cob floor, I’m adding about a pound of ground psyllium seed husk, which I just ordered from Amazon.  Adding the husk creates a soft floor, much like that of a tennis court.  Hello, happy knees!  Bonus: it’s also is good for constipation, though unlikely to take effect in floor form.

Random unrelated photo

Speaking of blockages, this creature is (guarding?) our side door that leads down the new stairs Rob built few weeks ago.

What kind of crazy zig-zaggdy web killing pattern IS this anyway?  It appeared this morning after the wasp supper yesterday.

As an obscure band once wrote, “If you see the spider eat the fly, then you know what you’ve got in life.” Must have been a depressed band. Hack, cough.


Next week’s plan

In addition to continuing the foundation, I plan to start building the roof to make it easier to keep the cob, the floor, and the rest of the site (such as future straw bales) dry.

After reading about roof-building in my cob books, I realize how much more work is ahead.  The foundation and roof building are very intimidating to me since they are critical to the building not collapsing or falling in on your head, and I’ve never built either.


Total costs to date


Week Cob item Cob cost
1 Used decorative door piece, wooden dish rack $2
3 Extra 4″ drainage pipe $6
4 Gravel $55
4 Portland Cement $16
4 Sand $15
5 More sand $15
5 4 glass block windows (from Scrap Exchange)
5 Psyllium husk for floor (with shipping)
TOTAL $136