Natural Paint & Plaster Overview
Before there were companies that made and sold building materials, people made
their own paints and plasters. It was part of common knowledge. And in many
cases, these older paint & plaster recipes are superior to what we purchase today.
Natural coatings use a variety of non-toxic ingredients to make beautiful, durable,
and incredibly forgiving finishes that invite experimentation and creativity. Recipes
vary depending on the performance needs and locally available ingredients.
All paints and plaster have a key characteristic in common: they all
contain some type of sticky binder. Precisely that stickiness explains why they
adhere to surfaces, like walls and ceilings. And the binder is what creates a cohesive
monolithic material. The binder is often what gives each natural coating it's name:
clay plaster, lime-wash, egg paint, etc.
The difference between paint and plaster is thickness. Paints are micro-
thin coatings, while plaster has a measurable thickness. Paints are applied with a
brush or roller in thin layers. Plaster is applied with a trowel...like spreading cream
cheese on a bagel. Because paints are applied thinly, they are inherently less viscous,
while plasters are generally stiffer.
Paints & plasters are coatings, applied over an existing substrate. They are not wall
systems. They are not structural. They are coatings. Used to create color and
texture. Which makes natural paints & plasters simple to integrate into any
building...existing or new construction.
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Best Use
Natural paints & plasters are extremely versatile and can be used on new construction or to renovate existing buildings.There is a natural coating suitable for most common applications...from exterior render to interior finishes...even inside a shower! Natural paints & plasters can be made yourself or purchased ready-to-use. So no matter your project goals, you can incorporate natural finishes!
ivory clay plaster & aqua tadelakt (polished lime) over strawbale walls
lime plaster with yellow iron oxide pigment remains durable with weather exposure
Cheat Sheet
CLAY WALLS
Binders for paints include: clay, lime, casein (milk protein), egg yolks, egg whites, and more.
Binders for plaster include: clay, lime, gypsum, and more.
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OTHER INGREDIENTS
A variety of other ingredients can augment the aesthetics or performance of natural paints & plasters. Such as: pigment, wheat paste, aggregate (sand), mica, chopped fiber, cattail fluff, cow or horse manure, etc.
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AT A GLANCE
non-toxic
free of petrochemicals
less energy to make
breathable (do not trap moisture)
inexpensive ingredients
very doable for novices
BEST USE
use in place of conventional paint or plaster
(making sure the substrate is compatible with the binder)
LINK TO GLOSSARY
Read the glossary description here.
clay plaster over cob walls and clay paint to create a game board on the floor
close-up of tadelakt, a Moroccan method for burnishing and sealing lime plaster
What's in Paint?
Because paints are applied in thin layers, they do not generally need extra
ingredients to give them structure. In other words, paint is made up of just three
simple ingredients:
1. Binder: this is the glue that holds the paint together and to the surface
2. Pigment: color added to the paint (this is usually the point of painting)
3. Solvent: whatever is used to thin the consistency of the paint (for many
natural paints, the solvent is water)
All three ingredients need to be compatible with each other and with the surface
they will be applied to. For example, some binders, such as lime, are highly alkaline
and so require pigments that will stay color-stable in high alkalinity. To determine
compatibility, simply paint a test area, let it dry, and see if it is easy to peel off.
What's in Plaster?
Because plasters are thick, and many binders shrink when they dry or cure, you
need to add aggregate and/or fiber to give them structure and to mitigate cracking.
This means you have four potential ingredients to play with, and endless possibilities
on what you create with them.
1. Binder: this is the glue that binds your plaster to the surface and creates a
cohesive material
2. Aggregate: fine or coarse construction-grade sand that gives the plaster
structure, strength, and shrinkage control
3. Fiber: an integral web of fiber inside the plaster provides resistance to
cracking and allows plaster to defy gravity (and be applied thickly)
4. Pigment: color added to the plaster
All ingredients need to be compatible with each other and with the surface they will
be applied to. The specific ratios of each ingredient depends on the binder, how thick
your application is, and your application technique. So testing is essential to find a
recipe that is suitable for your particular situation. Additionally, plaster is applied
with a trowel, which means you can use your tools to create any variety of finish
textures in the surface...from rough to polished smooth.
Benefits
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• Natural paints and plasters are non-toxic and free of petrochemicals
• Require very little energy to produce
• Finishes are vapor permeable, aka "breathable" (so do not trap humidity inside your walls)
• Inexpensive ingredients, generally less costly that purchasing manufactured paints or plasters
• Natural and completely biodegradable materials, that create a healthy indoor space
• When you make your own finishes, you control the ingredients (and the health of your space)
• You can make absolutely any color (you just might need to experiment a bit)
Challenges
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• Requires testing with new recipes to ensure compatibility with substrates, as well as overall performance and durability
• Requires test samples to ensure your recipe creates the color and texture you want
• Can be difficult to color match
• Ready-made products can be costly
• It can be intimidating to make your own products when we've been trained to purchase what we need...the solution is to start with something small, something temporary, until you gain your confidence and feel empowered
Performance
HEALTH
The single biggest benefit of using natural
paints & plasters is that they use non-
toxic ingredients. (Unlike commercial
paints that can contain carcinogens,
respiratory toxins, neurotoxins, and other
nasties.)
This is especially true if you make your
own natural paints & plasters. Then you
control every ingredient.
DURABILITY
One misperception is that you compromise
durability with natural finishes. This
couldn't be farther from the truth. In fact,
most of the oldest buildings on earth still
only have the original artisan-made paints &
plasters. So natural paints & plasters
can last centuries if made & applied
correctly.
Additionally, most natural finishes can be
sealed with breathable clear sealers, such as
hardening oils or beeswax paste, which
increase the hardness and/or washability of
the surface.
RELATIVE COSTS
Ingredients for natural paints and
plasters cost less than commercial
products. The list is simple: clay or lime
putty, sand, maybe some pigment. The total
material cost to paint an average room is
around $15. To plaster an average room, the
material cost is around $40.
Natural plasters provide additional
potential cost reduction in the form of
energy savings. Thick plasters add
uniform mass to the interior of a space,
which helps to reduce temperature
fluctuations inside. Less fluctuation
translates into less heating/cooling time.
Additionally, clay has the ability to regulate
humidity, which improves comfort and
reduces the need for air conditioning. (See
also "humidity control".)
PESTS
Pest/bug infestations are absolutely
not an issue with natural paints &
plasters. The cured paints & plasters do
not contain any food source nor do they
create a suitable habitat for bugs.
contrasting blue and brown clay plaster details
clay plasters create healthy spaces
burnished lime plaster with green pigment really reflects life!
natural plasters beg to be touched
FIRE RESISTANCE
Natural finishes are not inherently
flammable. Plasters in particular are akin
to a stone finish in terms of flammability. In
code-speak, they are designated as "non-
combustible materials" in accordance with
ASTM E136.
Natural paints & plasters do not foster
smoke development in a fire. Nor do they
release toxic chemicals in case of fire
(because there are no toxic chemical
ingredients).
Plasters do not change the fire resistance of
the wall itself, However, a thick plaster
finish slows the transfer of heat through a
wall. By thickness, 1/2" thick plaster slows
fire development by 1/2 hour, 1" thick
plaster slows by 1 hour, etc.
HUMIDITY CONTROL
Any material that stays persistently damp
can support mold growth. And any
biodegradable material that remains damp
will begin to decay in place.
Clay plasters in particular are hygroscopic.
This means they tend to absorb moisture
when an excess is present. In your space,
this means clay plaster will absorb moisture
out of the air any time the relative humidity
exceeds 50%. It then releases the humidity
when the air is dry (less than 50%). Thus
clay plaster regulates the humidity
inside a space, keeping you
comfortable.
The example I like to share is this:
When you take a hot shower in a
conventional space, the steam condenses on
any mirrors, fogging them up. In a
bathroom that has clay plaster walls, the
mirror does not fog up from your shower.
Note that the clay is not getting wet!
The humidity absorption/release is never
felt as a change in the dampness of your
plasters. The clay can absorb gallons and
gallons of water without any perceptible
change to the surface of your walls.
SIMPLICITY
The ingredient list is short: 3 for paint & 4
for plaster. This means getting started is
fast & unintimidating. And playing with
the infinite possibilities is inevitable...
yellow iron oxide in a white clay plaster, smoothed around a sculpted clay railing
clay plaster over cob walls and clay paint to create a game board on the floor
close-up of tadelakt, a Moroccan method for burnishing and sealing lime plaster
What can I plaster?
Natural plasters can be applied to nearly any substrate. What you need are 3
characteristics for your wall:
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1. Rigidity - this means the wall surface does not flex or flake, and does not show signs of movement cracks. A wall that is not rigid results in cracking plaster. If the wall is highly flexible, you will need to add rigidity. If there is any material that is flaking or dusting, it needs to be removed, and any holes would be patched. And if there are movement cracks, the structure should be stabilized before plastering.
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2. Texture - this means you need a lot of surface area for the plaster to interface with, because the plaster is heavy and needs a gripping surface to hang off the wall. Texture can be as simple as applying paint with coarse sand in it (if your plaster will be thin). Or it can be wooden lath that is spaced to create a grip for plaster to key in to.
3. Absorbency - ok, this on is technically optional, but it's highly beneficial. An absorbent surface allow small amounts of binder to actually pull into the wall substrate. This creates an even stronger bond between the plaster and the wall below.
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Then test your plaster on the surface you want to apply to. This way you can ensure the
plaster is compatible before you commit to a large area. And don't forget to dampen your
wall before plastering if it is absorbent!
Examples of surfaces compatible with clay or lime based plasters: wood lath, drywall with
sandy paint applied, strawbales, clay walls, unpainted concrete or block...and on and on...
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Other fun stuff
My niece is a project girl, through-and-through. Once when she came to visit, we pulled out some milk and set it in the sun to curd. We strained the curd and added water and
pigments and voila! we had made milk paint. With a small collection of pigments, she could mix any color her heart to dream up. I think we spent 3 hours painting at the dining table. And at the end she said "we should do this every time I visit".
And that is the beauty of natural paints. They are easy. Fun. All-natural. Stress-free.
Non-toxic. And addictive!
close-up of tadelakt, a Moroccan method for burnishing and sealing lime plaster
Recommended Reads
Here are my favorite books about natural paint and plasters (click the text link below each book)
