Here is a short video we made for San Diego’s Sustainable Building Week 2021 about how biogenic materials – such as straw – not only reduce the carbon emissions associated with construction, they can even trap and store carbon in buildings, helping to reverse climate change.
Running April 12 -16, 2021, Sustainable Building Week highlights local organizations going above and beyond in sustainability and improving our built environment. For more info and links to all the events, check out the website.
Now, some of their paint is not as bad as most (their Emerald line is recommended by the Healthy Building Network because it is APE-free, low-VOC, and low emissions) but it’s still paint: plastic-y, synthetic, not very close to natural wood and stone.
So I decided to make a clay plaster version of the color and I’m in love.
Natural plaster can’t fix the big problems in the world today but it can help you create a calm, beautiful sanctuary in your home.
Many of us have found ourselves spending more time at home recently and probably more time thinking about what it is to be healthy, both physically and emotionally. With so many uncertainties, many people are experiencing high levels of stress and are looking for ways to stay centered.
If you’ve found yourself at home, staring at the walls, you may have started to think more about what ‘home’ is, what you want your home to be. What would it take to create more beauty and a sense of calm in your home? What would make it feel more like a sanctuary that reflects your values and aesthetics?
This is what natural plasters can do. Natural plasters create a rich, subtle background. A natural plaster is one made with sand, a binder of clay or lime, mineral pigments, and no synthetic additives. Whether rustic and earthy or fine and polished, clay and lime plasters add deep visual interest and a sense of solidity to a space.
Have you ever found yourself inexplicably attracted to a photo of a room without being able to put your finger on what makes it so lovely? It might be the plaster. Look closely at the walls. Do they seem to have varying tones, depth of color, subtle texture? Then it’s probably plaster, the unsung hero of interior decor. Whether it’s bold texture or subtle color variation, nothing creates as much depth of interest on a wall as plaster.
Natural plasters beg to be touched and they feel like stone, whether it is polished marble or rough-hewn sandstone. They attract the eye and can create a calm canvas on which to meditate or an active work of art that inspires. Facets in the sand reflect the light, the depth of the surface creates tonal differences, and inclusions –such as black sand or mica– lend minute detail.
And there are additional benefits beyond beauty. Natural plasters contribute to better indoor air quality. They do not contain VOCs (volatile organic compounds) and will not off-gas when applied, so you are not building toxins into your home. Clay plaster has the miraculous ability to safely store extra humidity and then release it when the air is drier. This not only makes you feel more comfortable but helps to stop condensation that leads to mold growth. Clay plaster is softer than painted drywall, causing sound to bounce and echo less. Lime plaster has a very high pH, making it naturally antiseptic and anti-fungal. Both plasters have thermal mass which helps you hold on to your heat in the winter or cool in the summer.
Natural plasters are also better for the planet. Clay plasters require very little processing and have incredibly low embodied carbon. Lime plasters have lower embodied carbon than cement-based stuccos. Both types create less pollution than their synthetic counterparts.
No, natural plaster will not stop a global pandemic, fix racial inequality, or restore the economy. But it is very beautiful, it is good for your health, it is not bad for the planet, and it may help you find some precious sanctuary in these difficult times.
When I consider what plaster to use, I always think of clay plaster first. I love clay plaster, it has so much going for it.
In terms of minimizing environmental impact and carbon footprint, you cannot beat clay plaster. It is minimally processed, needs no additives, and can be sourced locally.
Building well with straw bales (and straw-clay, adobe, cob, and other natural building systems) requires an understanding of moisture: vapor permeability, diffusion, wicking, etc. This leads to needing to understand plasters.
Clay plaster is one of the most vapor-permeable finishes, coming in at 11 perms per 2″ of plaster. This makes it ideal for any building system where you do not want trapped moisture — which should be the goal for every building system but is often ignored in conventional construction.
Clay plaster has many benefits, but it does have some limitations. Once it gets wet enough, it will erode. It is also not as hard or impact-resistant as some finishes. Sometimes you need a plaster that can fulfill different duties. This is when I turn to lime plaster.
Lime plaster has a slightly lower carbon footprint than cement plaster and is more vapor-permeable than cement (lime plaster is 9 perms per 2″ where straight cement plaster is less than 1 perm per 2″).
If you do it right, lime plaster goes through a chemical change as it cures that effectively turns it back into limestone on the wall. It will not erode. It is harder and more impact-resistant than clay.
Lime plaster used to be very common in the US but was replaced by drywall and gypsum-based plasters in the last century. Then it became difficult to source lime of high enough quality to produce consistently good lime plaster. Although it is possible to make a good lime plaster from locally-available Type S lime, it requires knowledge, skill, and a fair bit of babying to succeed.
On larger-scale projects, like the exterior of a strawbale home in a climate that gets sideways monsoon rains, we will make our own Type S lime plaster, don our gloves and safety glass, apply the plaster skillfully before it begins to set, and then tend to it patiently until it has cured.
Hydraulic lime is another option. It still requires knowledge and skill, but it sets faster and more consistently with less babying. You could import hydraulic lime from Europe, where the tradition of lime plaster had not been broken, but at a high cost financially and environmentally.
So you can see why I gravitate towards clay plaster whenever possible. I encourage clients to build wrap-around-porches to take advantage of outdoor living and to allow for clay-plastered exterior walls.
On a smaller scale, like a bathroom, lime plasters are a little less daunting. When applied well and polished, lime plaster can look and feel like marble. When finished in the tadelakt tradition, by rubbing oil-based soap into the plaster before it has cured, it can be remarkably waterproof. But these thin veneer plasters leave little room for error or inconsistency, so I have been reluctant to sell them to clients.
I recently became aware of a product called Limestrong. It is a bagged lime plaster created by the talented plasterer Ryan Chivers, in partnership with other experts in plaster chemistry. In my mind, it is the lime equivalent of American Clay Plaster: a convenient, bagged, premeasured plaster with a tested range of pigments that allow you to create a consistent result time after time. And, like American Clay, you do pay more for this convenience.
At the 2020 Natural Plasterers’ Guild Retreat in January in Jacksonville, Oregon, I had a chance to learn more about Limestrong and see Ryan demonstrate the line of products.
Most importantly to me, Limestrong sources all of its ingredients from the US. Since lime itself has a larger carbon footprint due to the amount of heat needed to process it, keeping the embodied carbon involved in shipping as low as possible is important.
Limestrong uses pumice as the aggregate. This not only makes it lighter to ship (and carry around the job site), the pumice creates a mild pozzolanic effect, making the plaster slightly hydraulic. Although this means a faster set time, it also ensures a more even cure.
The only additive in Limestrong is cellulose, which is a non-toxic material that helps retard the set and acts as an adhesive to help it stick to difficult substrates like painted drywall.
So it is with great excitement that we have decided to host a professional plasterers’ training for Limestrong plasters at our current job site in Valley Center, CA, in March. We will learn directly from Ryan Chivers and his co-teacher Liz Johndrow about applying Limestrong over drywall. If time and interest permit, we may also install Limestrong over a clay plaster base coat on a straw bale wall. Attendees will also be able to observe two tadelakt shower surrounds being installed by our crew. Exciting stuff!
We are excited to announce that we are hosting a training in Limestrong lime plasters at our current job site! These natural, durable plasters are perfect for existing homes as well as new construction.
Join Ryan Chivers, owner and formulator of Limestrong Mineral Finishes, for a hands-on lime plaster weekend training at our current project in Valley Center, CA. Discover each of Limestrong’s beautiful finish plasters: Sand, Stone, Marble, Tadelakt and Limewash as we plaster inside a local residence. Instruction and lunch provided on Saturday and Sunday, 10 am – 4 pm.
What is Limestrong?
Limestrong is a dry, bagged lime plaster mix created by the talented plasterer Ryan Chivers, in partnership with other experts in plaster chemistry. It is the lime equivalent of American Clay Plaster: a convenient, bagged, premeasured plaster with a tested range of pigments that allow you to create a consistent result time after time.
Limestrong sources all of its ingredients from the US. Since lime itself has a relatively large carbon footprint due to the amount of heat needed to process it, keeping the embodied carbon involved in shipping as low as possible is important.
The aggregate in Limestrong is pumice. This not only makes it lighter to ship (and carry around the job site), the pumice creates a mild pozzolanic effect, making the plaster slightly hydraulic. Although this means a faster set time, it also ensures a more even cure. The only additive in Limestrong is cellulose, which is a non-toxic material that helps retard the set and acts as an adhesive to help it stick to difficult substrates like painted drywall.
If you would like to expand your range of plastering skills to include this beautiful, non-toxic, eco-friendly lime plaster system, join us for this informative and fun workshop.
* Some people have reported having issues with the registration page on Limestrong’s website. Make sure the number of tickets is set to at least 1 before clicking the registration button. If you are unable to sign up, please email email@example.com