Insulating Earth Plaster
Earth and clay, in and of themselves, are not insulating materials. They have thermal mass, which means they store heat (or cold), but don’t reduce the transmission of heat energy from inside to outside (or vice-versa). Nevertheless, you can make earth plaster more insulating if you need to. More on how to do that, and how well it insulates, later in the post.
Insulating a House Basic Overview
Before I get to the plaster game though, a quick overview of insulating houses in general: The first thing you need to worry about is not the walls, it’s the roof. That’s where 60% of your heat goes. High ceilings are notorious for energy wastage, as you have a fat layer of completely unused heat that skulks under the ceiling. Your floor is the next worst culprit for heat loss. This doesn’t mean you don’t want to insulate the walls. You do. Though sometimes insulating the north facing wall (or south facing in southern hemisphere) is enough. But insulating the walls without sorting out the roof is a bit pointless.
What is all this jabber about R and U values? If you’re a newbie builder you may be wondering. Insulation levels are measured in R values. Here’s a neat little infographic for US climate zones showing the kind of R values you would need for your roof, floor and walls for a conventional house in various climates. All building materials have an R value per inch, though be careful because calculating R values is a bit more complicated than just multiplying by inches. Some insulating materials work in different ways (for example, if you compress certain materials, or mix them into something like clay plaster, then you reduce their capacity to insulate). Nonetheless, the graphic gives a basic idea of what’s going on with R values.
Then there are U Values, which rate how energy efficient a given system will be. Me? I want to get back to earth plaster, but if you feel like geeking out on U Values as well here’s more info.
Ok, back to the plaster. First, let's be clear; Mixing insulating materials into your earth plaster alone isn’t going to cut the mustard in seriously cold climates. You’ll want to use the Other Ways to Insulate an Earthern Wall listed in the next section. But if you live in a temperate climate, or a place where you need a little extra oomph in the winter months, insulating plaster can work a treat.
Note: When using insulating plaster, you need to apply a thick layer (at least 3 inches). It's important to add the plaster to the exterior walls of the house for maximum insulation (though if you’re restoring a listed building, this may not be possible, in which case you’ll have to insulate the interior wall instead).
Other Ways to Insulate an Earthen Wall
If you live in a climate which remains below zero for months at a time, earth plaster alone is not going to be enough. I'm not discussing whether or not you should have built a mud home in a cold climate here, nor going into massive detail. There are a few ways of insulating earthen houses. Most of these require attaching a light lath or frame over your wall, and stuffing it with some sort of insulation such as:
Alternatively, you can cover the exterior of your mud house in straw bales (R 1.45 per inch).
I'm sure there other natural, insulating earth plaster methods out there. If you've tried something else, feel free to add it in the comments.
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4/5/2018 07:03:57 pm
Thanks Atulya. You helped me think through our insulation ideas. :) We have access to tons of free sawdust, so that will be our got insulator. I appreciate all of your help full posts. Blessings, Kit.
5/5/2018 11:21:16 am
Sawdust is a great insulating additive. Good luck with that Kit. Sounds like you have a great project on the go.
29/5/2019 10:08:29 am
1/11/2019 12:16:58 pm
here's one explanation of thermal mass:
4/1/2020 10:31:53 am
Nice Blog!! The content you have shared is very elaborative and informative. Thanks a lot for sharing such a great piece of knowledge with us.
6/12/2020 01:58:49 pm
8/1/2020 02:10:23 am
i want to build vacation homes and i live in the coast and summer gets very hot. Whats your suggestion ??
6/12/2020 02:01:39 pm
Well, it depends what resources you have on your land. If you are in an area with plenty of bamboo, that could be good. If you have a lot of clayey soil on your land, that would be my choice. If you have rocks, I'd build with rocks. My suggestion is to look at and listen to your land.
11/3/2020 07:06:17 am
Hey Atulya! You had done a great work dear on your blog. Your post with a unique title EARTH PLASTER MINI COURSE is interesting and wonderful to read. I am excitedly waiting for your next article to read. By the way, your post content is also looking so good and interesting with pictures. Keep it up.
6/12/2020 02:02:52 pm
12/4/2021 01:56:48 am
Thanks for this. I'm so inspired
12/4/2021 01:17:34 pm
A small mud house in the backyard is the perfect way to start! So glad you are inspired to go for it.
Nice blog. Happy to see your idea of writing blogs. It seems easy but it is not as the painting have to match the color as the house owner wants and the color preference is different of all home owner. Around a year ago I hire a painter on the recommendation of my relatives but not got the desired results as I was expecting. But now I understand that no one can full fill your all expectation in any field.
10/10/2021 12:21:31 pm
True! Better to do it yourself if you can. Cheaper, and no one else to blame:)
10/10/2021 09:38:30 am
thank you very much for the course of mud , we are building a rootcellar and it helpt a lot . I want to make the roof with mud but also on top making a garden , have you any sug. off don ts or does thank you very much . greatings from Spain .
10/10/2021 12:40:18 pm
So glad it helped. You want a living roof then. Take a look at my article on that here: https://www.themudhome.com/living-roofs.html
Atulya so appreciate all your work bringing ourselves together! And all this knowledge ! Along with your writer’s spin!!
5/1/2022 02:27:08 pm
I have a brick house from 1806 that my wife and kids and I are working on in upstate NY (Canadian boarder upstate) and I had purchased one of your courses about lime after I had already decided to use lime mortar and lime plaster on the brick but I still need to go through the course. I had planned to use slip straw for my insulative infill for my walls after I framed in the interior but most natural builders didn't have much advice about brick and those that did didn't recommend this for the fact that the brick may bring in moist air and the clay may not be able to negate it affects on the straw in the long run but I guess hempcrete is far better so I've decided to do that as my insulated infill then I plan on putting a clay plaster over that. I had purchased a whole bunch of dinged up drywall at the hardware store for 75% off before I decided on some of my plans so I figured I would use the drywall on my ceilings but I'm not sure of a good solution for insulation when it comes to my roof or ceilings when we get -30F and sometimes, but not in a few years, we get -50F in my area. The winters have been more mild the past handful of years but I can't guarantee that it'll stay that way. I wish wool wasn't so expensive because I like that idea for the ceilings and I hate the idea of using some of the more mainstream insulation aspects due to the healthy issues such as fiberglass insulation plus the chemicals that are all over the other stuff but if I had to choose one I'd probably go with rockwool despite the HUGE amount of energy that it takes to create the cotton candy style rock insulation. If anyone has any advice or direction I would greatly appreciate it. I mixed up 16-5gal buckets of slacked lime to use for mortor and plaster plus I still have 12 bags of high calcium hydrated lime to use. I sifted much of the sand that I have from the my land or a neighboring property to use as well. I dug up a bunch of pure clay to use but I'm not sure how to go about processing that part yet.
5/1/2022 02:40:11 pm
7/12/2022 09:30:43 am
Great post thankyoou
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