Earth plaster walls and earthen floor renovation [work in progress]

Hello folks,

The wife and I have just purchased our first home in the forests of Estonia and have started renovations. It is a small wood framed house around 70 years old. Lots to learn from you all!

As we peeled back the wallpaper, we were happy to find that once upon a time the walls were done with some kind of clay and earth fibre mixture.

Yesterday we mixed up our first clay mix from clay we dug up ourselves on the property, sand from nearby, and Cattail fibres. The clay is reddish / brown, and very clean. I couldn't detect any layers other than clay when doing a water jar test.

Ratio was about:
1 part sand (quite gritty)
.8 parts clay
.8 parts cattail (going on volume)

With all the wallpaper gone we were left with a fairly rough surface, and thought we'd do a test run and apply a clay plaster right onto it to see how it goes.

We added water until it felt about right. But actually had no real idea.

We applied it about one inch thick, and were happy that it even stuck. Even when curving it up from the wall to the roof a bit it continued to stick.

What I'm not sure about is if it is recommended to just apply a plaster like this straight onto a wall, or whether we should be stapling some sort of thatch (ie horizontal and vertical fibers along the wall) for extra support for the clay.

After a few hours, the clay was still there, and we were happy about that. In a few days we will return and fingers crossed it is still there. Since the old clay from eons ago we applied it to was fairly rough, I'm hoping there is a good chance it will be enough, but we don't want to be sitting there in the middle of winter with walls falling down.

A few questions:

With sand, how does a gritty / larger sand grain mix effect the clay compared to small grains? I understand smaller grains equals smoother end result, but does larger grains mean tougher / more durable? and less expandability / shrinking and i.e less cracking?

Would you use a larger grain sand for doing under layers of the wall, or perhaps doing the bass layers of an earthen floor, then use a smaller grain mix for doing surface layers?

Any tips or advice would be really appreciated!

Will continue to post pictures as we go so hopefully others might learn from our mistakes or so others might help us avoid making them along the way.

Many thanks,
Rob

Rob : You didn't mention wetting the old clay plaster before applying on new, the old stuff can suck so much water out of your new plaster it will fail before it can set up !

I am going to sound like a broken record here but - cobcottage.com Ianto Evans, Great Book 'The Hand-Sculpted House' and M. Smith's 'The Cobbers Companion '

Yadah ! Yadah! Yadah! Post here if you have any more questions Big AL !

Late Note : Three other places to look generally in the 'Cob Forum/Threads' specifically '' Clay 'slip' between layers of Cob'' and always look down at the bottom of the page
for the - '' Similar Threads " - Section ! Big AL

I will try and get these books from cobcottage.com now, but I seem to only be able to get printed books there, not ebooks.

We didn't wet the old clay wall actually! I wonder if it might be compensated by the fact that our clay mix was probably way too wet? Fingers crossed.

We just did a small section though like in the photo half expecting it to fail so we could learn something about the mixture. I knew we missed something but with no books or internet to lookup at the location we had to go on what we remembered from reading online.

Thanks for all the yadah Big Al

With the floor it is currently just wood (chip board it seems) that is sitting on top of bare soil.

The foundation of the house is sitting on concrete.

At the moment, we're thinking of digging down a foot, putting in about 6" of stones for drainage / dryness, and then ramming an earth floor on top.

I have heard of some people adding a plastic layer between the stones and clay floor, but we're not interested in using plastics.

So far with what I've described, what problems are there with this sort of approach? Does one need pipes amongst the rocks? Should sand be used?

Any pointers would be really helpful.

Thanks,
Rob

edit: I've started reading the Hand Sculpted House ebook now.

The problem with ramming directly on stones is the clay mix will work its way down into the stones, filling all voids and making them a waste of time.

You can use fabric instead of the plastic, but then you won't have a vapor barrier but just a sediment screen. Not a problem, just an observation.

Drainage pipes among the rocks could be useful if you expect water problems, but if your chipboard on soil is holding up you probably don't have water problems.

Tubes to run hot water hydronic heat are REALLY NICE to have and I strongly suggest adding them if you can afford it. Even if you can't afford the boiler now, put the pipes in while the floor is going in. My biggest regret in my current house is not doing that.

The chip board floors have started to give way in areas, but it doesn't seem too bad and not as a result of there being too much water. The planks are anywhere from 10 - 20 years old. I am assuming then the drainage around the foundations is ok. The house is also surrounded by a 1 meter moat which looks like it directs heavy rains into the forest.

R. Scott, I thought the clay might go down with the rocks, creating a ladder for moisture to climb up, defeating the purpose of going to the trouble of bringing in all these rocks. I wonder if a bed of smaller rocks, on top the larger rocks might fill those gaps would prevent this... perhaps then a layer of large grained sand on top of the smallest rocks might do the trick and act like a plastic sheet?

Instead of this, can other ingredients be added to the floor mix to increase its water resistance, such as Cow Manure or Lime? It seems to me very resource intensive and counter intuitive to fill a large base area of the house with rocks from the creek.

We have been wondering about whether we will add heating tubes to the floor or not. I should do more research on this before we go ahead. Thanks R!

Hi Rob,

I have been following along on this one. Good advice all around. Your recent post though has some "hole" in your logic If you take a jar and put stones, little pebbles and sand in it, in that order and shake...you end up with the big stuff on top and the little stuff (sand) on bottom. That same thing happens (over time) if you don't have a matrix separating them. We use geotextile cloth between our larger rock and finer particulate matter, be it sand, clay or whatever. I have also used plastic if there is a moisture issue, but that wasn't really a good idea, (we went back and changed that one!) as the moisture issue should be delt with first. If you don't have a moisture issue, and it doesn't sound like you do, then you must use something to seperart the clay cobb of your floor from the "drainage bed."

Here are a list of natural and traditional "margin materials," to consider.

Damp news print 5 cours thick minimum.

Grass or straw laid as a matting.

Recycle carpet or carpet padding (not the foam type.)

Recycle window screening (I would only use the nylon type as metal will oxidize and decompose to nothing)

Burlap sacks laid as matting. This is done a minimum of to course thick and each course is "clayed" before laying.

I am sure there are others that I have forgotten,

Good luck,

jay

I forgot, for "water proofing," read about Tadelakt methods.

Jay C. White Cloud wrote:Hi Rob,

I have been following along on this one. Good advice all around. Your recent post though has some "hole" in your logic If you take a jar and put stones, little pebbles and sand in it, in that order and shake...you end up with the big stuff on top and the little stuff (sand) on bottom. That same thing happens (over time) if you don't have a matrix separating them. We use geotextile cloth between our larger rock and finer particulate matter, be it sand, clay or whatever. I have also used plastic if there is a moisture issue, but that wasn't really a good idea, (we went back and changed that one!) as the moisture issue should be delt with first. If you don't have a moisture issue, and it doesn't sound like you do, then you must use something to seperart the clay cobb of your floor from the "drainage bed."

That makes perfect sense.

Jay C. White Cloud wrote:Hi Rob,


Here are a list of natural and traditional "margin materials," to consider.

Damp news print 5 cours thick minimum.

Grass or straw laid as a matting.

Recycle carpet or carpet padding (not the foam type.)

Recycle window screening (I would only use the nylon type as metal will oxidize and decompose to nothing)

Burlap sacks laid as matting. This is done a minimum of to course thick and each course is "clayed" before laying.

I am sure there are others that I have forgotten,

Good luck,

jay

Thanks for explaining all that Jay! Defining the lingo is helpful as well. I didn't know what a margin material was but I'd seen it around the place.

I think we're going to go with straw out of this list, as it is something we can access easily enough. How thick would you make this straw layer?

If you go with straw, mix it with "clay slip" and it should be a minimum of 20mm thick for the "margin" of "stratum" layer between the gravel and the cobb floor matrix, which will (should) go down in at least three "lifts" with no single lift being thinker that 100mm.

Hope that helps.

Regards,

jay

You inspired me to google search "The Hand-Sculpted House". One of the first results that comes up is a PDF scan. It'd be better to buy the book and support the authors, but if you need the info now...

Also, abebooks.com is useful to find new and second hand books. Unfortunately, when clicking "Destination, Rates & Speeds" to get shipping, it only allows certain countries to be default. I usually set it as Switzerland since that is reasonably close to Slovakia, then sort the results by cost including shipping.

Usually it takes books from Britain a week or two to get here.

Jay C. White Cloud wrote:If you go with straw, mix it with "clay slip" and it should be a minimum of 20mm thick for the "margin" of "stratum" layer between the gravel and the cobb floor matrix, which will (should) go down in at least three "lifts" with no single lift being thinker that 100mm.

Thanks for this Jay. With this clay slip, I'm guessing the straw should be just dipped into the clay slip, and then only applied to the drainage bed once it is no longer dripping anything. Or should it actually be dry before putting it down?

Hi Rob,

It goes down "soupy" (or "soppy," depending on you accent) so it will form a rather nice little matrix of stone, straw and clay. This layer is your natural "geo cloth" concept at work.

Andrew Ray wrote:You inspired me to google search "The Hand-Sculpted House". One of the first results that comes up is a PDF scan. It'd be better to buy the book and support the authors, but if you need the info now...

Also, abebooks.com is useful to find new and second hand books. Unfortunately, when clicking "Destination, Rates & Speeds" to get shipping, it only allows certain countries to be default. I usually set it as Switzerland since that is reasonably close to Slovakia, then sort the results by cost including shipping.

Usually it takes books from Britain a week or two to get here.

Thanks a lot for this Andrew. I found that PDF as well. I am going to order to the book now - it takes it seems about the same time for books to get from UK here to Estonia. Cheers!

Jay C. White Cloud wrote:Hi Rob,

It goes down "soupy" (or "soppy," depending on you accent) so it will form a rather nice little matrix of stone, straw and clay. This layer is your natural "geo cloth" concept at work.

Ahh I see. So it is ok if the soppy-ness goes down a bit, but just not all the way? Because if it goes all the way that would create a ladder for the moisture to climb, wouldn't it?

Yes it would create a "ladder effect." However, your gravel bed should be at least 150 mm thick (if not more) and even with the soupiest straw-clay matrix (thin pancake batter as an example) penetration would only be another 50 mm past straw. For floors I like a thicker clay slip mix with the straw just to curtail the penetration depth into the stone matrix.