Mike Harris

Phil Stevens wrote:

Mike Harris wrote:
This was going to be my next experiment with char as building material. What were your reasons for adding char to your mix? Insulation, weight, or something else?

All of the above, plus tensile strength, humidity control, and the principle of sequestering carbon within the structure. I've spent the past two days (with help) and have most of the interior wall packed and tamped, and so far we have used nearly half a cubic meter of biochar. When I have a few spare moments I'll start a thread detailing the project.

Steve, properly made biochar has no detectable odour and instead is good at absorbing and neutralising smells. When charcoal has a smoky aroma that is a sign that the production temperature was insufficient to convert all of the volatile hydrocarbons. I have a story about a biochar retort design gone wrong and the sweet smell of failure that I'll turn into a thread soon (one of my holiday projects is to document some of this stuff).

Interesting! Definitely keen to read about your experiments. Do you find the addition of char slows down the drying time significantly?

Ben Brownell wrote: I would also point out one potential issue is the degree of bonding between charcoal and soil/clay or other fill materials. For earth bag/rammed earth you need pretty good binding compaction, or else the strength of the wall is merely the strength of the thin plastic sack material it's packed in (plus any plaster coat). Charcoal can be pretty dusty/flakey and prone to de-stick-ifying earthen mixes. Definitely run some small experiments first and play with both the proportions and the sequencing of addition. I think it's possible to make it work, but be careful if the entire house is literally relying on it!

Good points Ben. Certainly wouldn't be putting too significant an amount in the earth bags due to structural concerns. Although char's superior water wicking ability rules it out for this application in my scenario anyway.

My first experiment with char as building material was giving the pizza oven a replaster. I have a fresh batch of site soil (some sand, some clay, mostly gravel) that I wanted to test anyway, so nice excuse to fling some mud.

I found that the more char I added (up to 50% char/sand + clay + water, no fiber) the fewer cracks in the plaster. I kept all other ratios the same for the experiment. It was a bit weird using such light (in weight, not colour) plaster.

Steve Zoma wrote:I am not so sure it would smell good either.

My fire[place in this old Victorian was taken out in the 1980's sometime. On damp days I can still smell the soot from wood fires kindled 40 years ago. I would think the bichar as insulation would continuously make your house small like woodsmoke as the moisture migrated inward.

I am not sure you would want a house permeated with that smell.

Of anyone who has had a partial house fire where the insurance company did not condemn the house afterwards, one of the complaints was always having that smoke smell on damp days.

The last thing I would want is to go out for a nice meal with the wife and have people in the restaurant sniffing the air because we smell like wood smoke and became nose blind to it. I think that would defeat an otherwise nice date night.

I've not noticed a smell from the biochar I've made, although I've kept it all dry until it's added to the plaster mix. Certainly something to consider. As far as I understand, properly charred char has all the smelly stuff charred away.

Phil Stevens wrote:I'm putting biochar into light earth infill and so far it's going well. I'm using big chunky stuff, 1-5 cm mostly. It is bone dry to start with, but it's absorbing some of the water in the clay slurry as we mix and tamp the material.

This was going to be my next experiment with char as building material. What were your reasons for adding char to your mix? Insulation, weight, or something else?

Thanks Douglas. Moisture is my primary concern too -- especially considering the walls on top will be straw bale. I suppose a moisture barrier wrapping the char filled bags could work, but I'd like to reduce the plastic used in the build too.

Maybe I'll stick to experimenting with char in the plaster instead.

Anybody have any experience with this?

We're planning on building a strawbale house on an earthbag stem wall. Climate is temperate so nothing too extreme. Pumice, volcanic rock, scoria etc are way too expensive to be an option around here.

I've started making biochar out of the invasive trees we've been clearing. I made a char heavy clay plaster to give the pizza oven a fresh coat and got me thinking -- would the char work as insulation in a highly compacted earthbag stem wall?

What are the potential drawbacks? Char absorbs water, so moisture wicking would be a factor I imagine. Probably wouldn't work on it's own, but might be helpful as an additive? Thoughts?

Hi Emily,

I'm not an expert -- more an enthusiastic enthusiast.

But the way I understand it is that clay walls will be just fine in your region if you take the necessary precautions.

If you're able to stop your walls from coming into contact with driving rain, you should be good. Which means your walls should be raised high enough off the ground to account for splashback, and your roof overhangs should be deep enough to protect the walls from rain.

What I'm concerned about is when you say the walls will be 'sealed'. Sealed with what exactly?

Clay walls are problematic when they're sealed in such a way that prevents water vapour from exiting the wall -- like with concrete or plastic paint. The moisture then becomes trapped in the wall leading to failure. Many heritage building are destroyed by using the incorrect materials for renovation.

If you're sealing your walls with something breathable -- like mineral paints or a natural plaster -- the vapour will be able to pass through this barrier and exit the wall, leaving it dry.

I abandoned it when old mate spent 100 + pages (not sure exactly due to aforementioned abandonment) describing whales and their history. Getting to the point wasn't one of his strong points

You might be able to look at some phase change materials that are used in greenhouses. They seem like they might be more lightweight than a brick wall.

But honestly, I would just do what people do for fireplaces and things like that. They build a stronger foundation under that one section. Maybe cement, maybe brick, maybe stone, but instead of wooden piers, you might have like a 6x4 area that is solid (or a wall filled with rubble) under the fireplace. In your case it could be a brick or stone wall of some sort. I think most of the time they build it solid up through, and build the floor around it. In your case, you probably want some sort of insulation break between the support and the actual mass in your house... but then again, maybe not. That piece would be beyond my experience.

I think I might go this route. With our very temperate climate, a fireplace or 2 is more than enough. Especially in a properly insulated house.

A quarry tile floor would add a bit of thermal mass.

Nice, hadn't thought of that one. We might be able to have a small section of quarry tile in the right spot to pick up some warmth

I assume you want the mass as a cooling factor?  

Make the walls thicker than normal walls.

Make the walls out of concrete blocks [the hollow kind] or adobe bricks.

What kind of cellulose?  Paper might be lighter than sawdust.

I want the mass to regulate the indoor temperatures. While it is temperate, we do have major swings to either extreme every now and then and they're just getting worse. Walls will be plenty thick cause we're building out of strawbale.

The cellulose we have available here is paper so works in my favour.

With a foundation of wooden beams on piers I worry about overloading it, especially as you are on a slope. Please consult a structural engineer!

That said, have you looked into the feasibility and potential effectiveness of doing a water wall? Basically a large water tank built into a south-facing wall, typically below the windows; it acts as a thermal mass. You might even be able to do this underneath the structure between the piers.

We were looking into incorporating our water storage and thermal mass into one system, but abandoned the idea because the engineering looked a bit more involved than we're going for. Might revisit this one though, thank you!

Hey folks,

We’re gearing up to build a strawbale house at any moment and wondering about thermal mass inside the building.

We’ll be building on a raised pier foundation due to the slope of the site. We’ll use a wooden girder and joist system on a grid of piers. We’ll  insulate the floor with cellulose.

I’m wondering about how to bring thermal mass into the building?

We’ll use earthen plasters throughout, but I’m not sure that will provide enough thermal mass to make any difference.

Is there a light-er weight mass material we can use in the floor? Something else I haven’t thought of?

We’re in a temperate climate (doesn’t get below freezing) so it’s not THAT big of a deal. But I’d like to have some sort of thermal mass inside the building to regulate the temperature

Thanks Nancy. Your points make sense.

The water is coming from a tarred access road and will drain down a steep slope in an unused part of the property. So once it's left the driveway it shouldn't be a problem any longer. I plan to build up the downward side of the driveway somewhat and line it with earthbags -- so if the gravel is laid and compacted correctly, it won't have much room for downward migration. Hopefully!

I think I'll cut the drainage lines across the track like in the video and full with gravel.

Hey folks,

I have a puddle in my driveway and it’s rather inconvenient.

I’m planning to fix the problem shortly by building up one side with earthbags and then layering gravel, sand, roadbase etc until it reaches desired height.

The soil is heavy clay, we have no risk of freezing, and it rains a lot.

My question is to do with the drainage underneath. I need some input - my neighbors and I can’t agree.

3 photos below.

First, the driveway in question. As the person taking the photo stands, the land slopes towards the left as well as towards behind the person.

Second photo: my solution. Red line is perforated drainage pipe in the gravel layer running parallel to the driveway and then exiting out the side when appropriate.

Third photo is another option, with many sections of drainage pipe running perpendicular to the driveway instead.

Significant wet spots indicated with water droplets.

Any thoughts/experiences/ about which of these options would perform better?