Tag Archives for " remediation "

Phytoremediation Cleans Up Soil Naturally

It’s happened to the most careful and graceful of us: a cup of coffee or plate of spaghetti sauce lands on the carpet, upside-down, of course. Out come the carpet cleaners, vacuum cleaner, or if you’re really prepared, the carpet-cleaning machine, and we do our best to treat the area and cordon it off for “drying”.  If the offending stain doesn’t appear again, case closed.

But what if you or someone else spills a toxic chemical on a large area of your lawn?  How do you remove that? There are no “lawn cleaners”...or maybe there are. 

The Environmental Protection Agency (EPA) is the U.S. agency concerned with not only monitoring, but cleaning up those big spills or more unfortunately “dumps” in the U.S.  It mandates how the sites are cleaned up and should hold individuals or corporations liable for the damage.  Unfortunately, as long as there is industry, there will be accidental, and often intentional, spill on land and water.  However, sometimes, the “cleanup” may not look like cleanup at all, if phytoremediation is used.  A toxic waste cleanup site may look like any other green field.

Phytoremediation refers to the different ways plants can be used to “clean up” contaminated soil.  Around  400  species  of  plants are called “hyperaccumulators” because they absorb unusually large amounts of metals in comparison to other plants.   These  plants  have  been found to accumulate metals at a rate 50 - 100 times higher than normal plants.  (Phytoremediation of soil metals)  They do this in a number of ways; the following terms are taken from the EPA’s Phytoremediation Resource Guide:

• Phytoextraction: some plants take up metal contaminants in the soil by plant roots and move them into the aboveground portions (stems, leaves, fruit). 

• Rhizofiltration: some plants adsorb contaminants from ground water onto their roots, or in the case of aquatic species, the plants live in contaminated water (like wastewater). Duckweed is a species that has been shown to remove many types of heavy metals from water. (Duckweed: A Model for Phytoremediation Technology)

• Phytostabilization: some plants are used to immobilize contaminants in the soil and ground water through absorption and accumulation by roots, adsorption onto roots, or precipitation within the root zone. This process reduces the mobility of the contaminant and prevents migration to the ground water or air, and it reduces bioavailability for entry into the food chain.

• Phytodegradation: some plants take up contaminants and break them down through metabolic processes within the plant, or through the effect of compounds (such as enzymes) produced by the plants. Pollutants are degraded, incorporated into the plant tissues, and used as nutrients.

• Rhizodegradation:  the breakdown of contaminants in the soil through microbial activity that is enhanced by the presence of the rhizosphere and is a much slower process than phytodegradation. Microorganisms (yeast, fungi, or bacteria) consume and digest organic substances for nutrition and energy.  This is becoming a very popular topic and technology as scientists learn how to modify and genetically engineer microbes for particular purposes.   

• Phytovolatilization:  some plants are able to take up and transpire (breathe out) contaminants, releasing the contaminant or a modified form of the contaminant to the atmosphere.  It is known that trees with deep roots transpire radon from the ground and groundwater.  

So, once the area is planted with hyperaccumulating plants, what happens next?  Unless the contaminant is phytodegraded, meaning, the plant breaks it down, the plants will still contain the contaminants, so they must be harvested and disposed of properly.  If testing reveals that they indeed have higher-than-acceptable levels of the contaminants (actually, this is a good outcome), they are either composted or dried and incinerated, and the waste remaining is securely buried.  Then the process is repeated until the soil is cleaned to an acceptable level.  The difference between phytoremediation and traditional soil removal is huge:  typically the amount of material to be incinerated from phytoremediation is only 10% of that required by traditional soil removal.   Here is a video of an EPA phytoremediation project in Crozet, VA where arsenic is removed from the site of an old apple orchard by planting and harvesting ferns that were bioengineered for the purpose of extracting arsenic.

What does this mean for the average homeowner?  Unfortunately, many private lands are poisoned with any number of contaminants: lead paint from old buildings, pesticides from farms and aerial contaminants that settle from spraying for insects or crops are all sources of contaminants.   You might not even be aware of old fuel tanks or lines that were buried decades ago, before you purchased the land, and have begun to leak, or maybe a new industry is releasing chemicals upstream of your land.  With any knowledge or suspicion of contamination, consider if you or your family will be exposed to the soil, and decide whether to get the soil tested.  If children or animals are regularly in contact with the soil, or you want to grow edible plants and vegetables on the land, testing is a good idea, so you know what chemicals you’re dealing with and which plants may be able to help you!  Here is a great article on how to gather soil samples and available testing centers. 

If you do find contamination on your land, here are some actual plants that could help clean up the soil: 

• Grasses: Indian Grass has the ability to detoxify common agrochemical residues such as pesticides and herbicides. Indian Grass is one of nine members of grasses that assist in phytoremediation plants. When planted on farmland, the reduction of pesticides and herbicides is significant. This list also includes Buffalo grass and Western wheatgrass, both capable of absorbing hydrocarbons from the land. (Phytoremediation Plants Used to Clean Contaminated Soil)

• Sunflower plants were demonstrated to have removed 95 percent of uranium from a contaminated area in a 24-hour period. This highly successful crop is a powerful tool for the environment because of its ability to remove radioactive metals from superficial groundwater, so they were used in cleanup after the Chernobyl nuclear disaster, which left nearby soil and water heavy with the radioactive elements cesium and strontium. The process works because the isotopes “mimic” nutrients that the sunflower would naturally absorb – cesium mimics potassium, which plants need for photosynthesis, and strontium passes for calcium, which provides structural support. Unfortunately, sunflowers did not work so well for Fukushima, Japan, because the isotopes released were very different from Chernobyl. (Why Scientists Plant Sunflowers After Nuclear Disasters).  Sunflowers are also good at absorbing metals such as lead, arsenic, zinc, chromium, copper and manganese. Indian mustard removes lead, selenium, zinc, mercury and copper.  Hydrangeas draw out aluminum from the soil.  (Superplants clean up toxins from contaminated soil)

• Trees can do their part:  Willows and poplars have been shown to be strong phytoremediators, not to mention being beautiful.  Carbon tetrachloride, a well-known carcinogen, is easily absorbed by poplar tree roots. They can also degrade petroleum hydrocarbons like benzene or paint thinners that have accidentally spilled onto the soil. (Phytoremediation Plants Used to Clean Contaminated Soil)

• Vegetables:  Of course, if you know that there’s soil contamination and you grow vegetables to remove it, you must take care not to let anyone or any animals eat the vegetables or plants.  Certain vegetables only take contaminants into their root systems, but others draw them up into the leafy greens of the plants.  Cruciferous vegetables like broccoli, kale, collards, mustards and also corn are considered hyperaccumulators.  (Superplants clean up toxins from contaminated soil)

• Mushrooms: Like phytoremediation, mycoremediation is the use of fungus or microbes to clean the soil.  It’s hard to believe that edible mushrooms are in the same class as toxic mold, but they are both fungus, and can be used to absorb and/or break down pollutants.  As mycelium spreads, it secretes enzymes which can break down pollution.  For example, oyster mushrooms have been used to remove E. Coli from Chicago River water, harmful Polycyclic aromatic hydrocarbons (PAHs) and TNT from water sources contaminated by wildfire ash, and diesel-contaminated fields from 10,000 parts per million (ppm) of PAHs to less than 200 ppm in eight weeks.  Turkey Tail, Shiitake and White-Rot Fungus are three other useful mycoremediators. (Mycoremediation: 8 Ways Mushrooms Can Mitigate Pollution)

The downside of hyperaccumulating plants is when they are grown and consumed without testing/regulation of the contaminants in them.  Unfortunately, brown and white rice (they are the same grain; brown rice is simply the whole grain while white rice has been milled and polished) are hyperaccumulators of cadmium and arsenic.  Arsenic is a more common pollutant; in the US, it gets into rice through pesticides used in old cotton fields that are flooded to farm rice, and through contaminated groundwater that floods fields in Bangladesh, for example.  The rice plant often takes up arsenic in place of silicon; rice plants require large amounts of silicon for optimal growth, and the chemical form of arsenite (AsIII) is very similar to silicon.  (Arsenic Transport in Rice and Biological Solutions to Reduce Arsenic Risk from Rice)  This is a very serious problem in eastern cultures where rice is a main staple of the diet for millions of people, and even those who can’t eat gluten, a protein in wheat that causes severe allergies in some people.

Unless you are reclaiming a swamp, new pristine land is not being created in great quantities, so we’re left with land that has centuries or millennia of human footprints, including toxic chemicals and metals.  Human use of the land in general leaves it in worse condition, but with the right plants, it’s possible to reverse a lot of the contamination.  If you want to make your own land–whether it’s your suburban backyard or acres in the country–cleaner and more habitable, get the soil tested and research which hyperaccumulating plants will make it better.  Once you get past the latin plant classifications, you may find the right plants also bring aesthetic beauty you wouldn’t have imagined. 

Fire and Smoke Recovery

Wildfires have been very destructive in the western half of the US in the late 2010's and early 2020’s.  As for the future, a 2022 report by the UN Environment Programme (UNEP) and GRID-Arendal projects an increase in extreme fires by 14% by 2030, 30% by the end of 2050, and 50% by 2100, due to climate change and land-use change. (breezometer.com)  

Fire disasters, like natural disasters, do not just destroy what the fire touches.  They can disrupt major infrastructures like highways and railways, power and water, and most important, air quality.  Because fires may smolder for some time, try to prepare to deal with the effects for weeks. 

If you live in an area prone to wildfires or prevailing winds that may carry smoke, here are some ways to prepare:

• Seal doors and windows with weatherstripping, caulk and door sweeps.  
• Find out how to adjust your HVAC system accordingly: you’ll want to close the fresh air intake and change over to recirculation, no matter whether you have central AC, a window air conditioner or portable air conditioner.
• Purchase extra MERV 13 or higher filters for your HVAC system, to be used on poor air quality days.
• If you live in an apartment building or condo with little control over the HVAC, consider purchasing vent filter material so you can place them in the vents into your space. Carbon vent filter material will neutralize many VOCs as well.
• Purchase a HEPA air cleaner (non-ozone producing type) and be sure to have an extra filter or two on hand.    
• Keep a number of N95 respirator masks on hand.    
• Keep canned food and bottled water on hand.
• Stock up on essentials for cleaning smoke odor: baking soda, white vinegar, rags, TotalClean

During:

• Try not to cook during a wildfire emergency, because cooking indoors increases small particulates and vapors in the air, and you won’t want to turn on your stove exhaust, as that will draw polluted outdoor air into the house.  Try to use just the canned food you have on hand.
• Monitor the filters in your HVAC system and air purifiers and change them when you start to notice a color change on the front of the filter, or when the output air starts to smell like smoke. 
• Check your local air quality and receive updates from airnow.gov . Fire and smoke maps are available under the heading fire.airnow.gov.  You can also register for a free 14-day trial of Breezometer’s Air Quality app.  Below is a diagram to understand air quality index values (airnow.gov).
• Use N95 respirators to evacuate to a safer place if necessary.  

Source: airnow.gov

After:  

• Don’t open windows and doors until the air quality index is less than 100.  When that happens, you can open windows fully to get more fresh air ventilation. 
• Set up fans near doors and windows to “push” smoke odor and soot outside.

To remove smoke odor that infiltrated from outside, or if you had a fire in your home:

• Run air purifier(s) continuously with charcoal filters. 
• Sprinkle baking soda over carpets and rugs and leave it overnight.  Then using a vacuum with HEPA filter, vacuum out the carpets.  
• Remove drapes, towels, and any hanging fabric exposed to smoke, and either launder it in your washing machine or send it for professional cleaning.  When washing it yourself, you can add a cup of distilled white vinegar to your regular laundry detergent to remove smoke.  Don’t machine dry the item until the odor has been removed; it may need an additional washing cycle.
• Wipe down all hard surfaces, including walls, ceilings, floors and windows with TotalClean or a 1:1 mixture of warm water and white vinegar (TotalClean is more gentle than vinegar and can be used on stone, wood, etc.)  Dispose of rags or wash them out with mild detergent and water as you go.  

To clean fabric-upholstered items:

• Try to remove any cushion covers that are washable.  
• Clean bare foam cushions by using “air replacement”:  Place the cushion into a large vacuum-seal bag and sprinkle baking soda over it.  Seal the bag and use your HEPA vacuum to remove the air from inside the cushion.  Let the air back into the bag to re-inflate the cushion.   Repeat several times if necessary. 
• Sprinkle baking soda over the piece and let it set overnight before vacuuming it off.
• You can also move the piece outside to air it out in the sun.  
• It’s difficult to remove smoke that’s settled into furniture, however, if it does not dissipate following using an ozone generator, you can contact a restoration company for their services if it’s a valuable piece to you.

Try an Ozone Generator to remove smoke odors:

• Ozone generators should only be used once all surfaces that can be cleaned are thoroughly cleaned (walls, floors and ceilings too!).  
• Ozone is not as effective in areas of high humidity, so running the air conditioner or a dehumidifier in the space to get the humidity down (60% or less) is advisable.  Central air conditioning and any exhaust fans must be shut down when using the ozone generator, though, because you’ll want the ozone to stay in the space. 
• Use fan(s) within the space to circulate the ozone.
• Ozone generators cannot be used in the presence of people, pets or plants, but once these are removed, they can be quite effective in removing smoke.  Follow all instructions to seal up the space and allow it to work for the full time advised before ventilating.  Contact HypoAir regarding rental of our ozone generators, or local restoration companies may rent ozone generators.    

For large areas with open walls and ceilings such as basements, garages or gutted homes, consider having them soda blasted by professionals to remove soot and smoke odor from the structure in hard-to-reach places.  Baking soda’s legendary cleaning and odor-absorption qualities can produce amazing results when combined with commercial equipment and a skilled contractor.

Don’t: 

• Spray deodorizers or fresheners to “cover up” the smell of smoke, because they do nothing to remove the contaminants, and many have toxic ingredients in them.
• Attempt to live in spaces with heavy smoke damage until they are cleaned.  “Third-hand smoke” is the term used for the way carbon and chemicals in the smoke react to the materials in your home, and it can make you very ill.
• Neglect flood remediation if the smoke damage was part of a fire in your home and fire response crews extinguished it using water.  Building materials must be removed or dried thoroughly within 48 hours in order to prevent mold growth. 

Ancient homebuilding 101: How did ancient people prevent mold in their homes?

Mold is an ancient problem, the most infamous account of which is in the 14th chapter of the book of Leviticus in the Bible.   Although it’s described as a “plague of leprosy” in the King James translation (verse 34), the references to “ingrained streaks, greenish or reddish, which appear to be deep in the wall” (verse 37 in New King James translation) are hallmarks of mold.  Indeed, some scholars investigating the meaning of the Hebrew word “Tsara’at” that was translated “leprosy” have inferred from ancient skeletal evidence and modern symptoms of mold exposure that a better translation may have been “mold”.  (Mold: “Tsara’at,” Leviticus, and the History of a Confusion).  Going forward with this assumption, the prescription for mold in the ancient Hebrew home was inspection (by the priest), identification (by shutting up the house and seeing if the mold grew), remediation (empty the house of everything valuable, remove the stones and plaster, and replace them with new stones and plaster), reinspection and cleansing, and in the case of last resort, demolition (complete dismantling and removal of the house). 

Has the problem (or plague) of mold gotten worse since ancient times?  Maybe so.  After World War II, a housing boom generated the need for faster and cheaper construction and made gypsum wallboard (drywall) much more popular than plaster as a building material.  Drywall is composed of compressed gypsum between two layers of durable paper. Gypsum readily absorbs water and dries slowly, while paper supports mold growth very readily. Since mold growth can occur within 24-48 hours of a water event, according to the US EPA, this is a perfect recipe for mold growth (just add water!).

The housing boom also caused quality of construction to decrease as volume increased, allowing for water problems to happen more frequently. “Back in the days of plaster, brick and stone construction, we didn’t have mold problems like we do now. This is in part because mold doesn’t grow on those materials very easily, if at all. Drywall, on the other hand, is like a Petri dish. What’s worse is that drywall is an ideal growth medium for Stachybotrys, the black toxic mold referenced above, because of its high cellulose content. Nearly every mold will grow on drywall given the right moisture levels, but Stachybotrys has a field day with it.  The final component of the perfect storm, which has made mold into the problem we now face as a society, here and internationally, is that our buildings are built so tightly, in the name of energy efficiency. Ever since the fuel crisis in the 70’s, there has been a huge push to reduce energy usage and create a more comfortable living environment. We have walls stuffed thick with fluffy insulation. Having a small utility bill is a bragging right at cocktail parties.” (A Brief History of Mold)

We can see that there are three things we need to consider in homebuilding to prevent the dreaded “m” word: design (for natural ventilation), construction technique (to avoid water intrusion and decay) and materials.  Here are two examples of how ancient people incorporated these mold-fighting aspects into their homes, knowingly or unknowingly:  one is from Israel and the other is from Egypt.

Building techniques in first-century Israel:

According to nazarethvillage.com, villagers in Israel often built homes on the bare ground.  They could dig into soft limestone to make caves for water or wine storage, but often just used what the topography offered.  “Building on sloping bedrock requires great care in setting the first course, starting from the lowest part of the foundation and working upwards step by step. The bedrock footing is flattened and slightly stepped, but does not need to be completely level. By fitting stones into the uneven footing, the force of gravity will secure the buildings onto the bedrock. Using the land as the ancients did makes a lot of sense – there is less to dig and less to build.”  (Site Excavation)  The mortar used to hold the stones together was primarily earth, chalk (calcium carbonate), leftover straw (to add strength and reduce cracking) and a small amount of hydrated lime for durability.  The chalk is excellent at absorbing excess moisture from the air (reducing humidity inside), while the lime also inhibits fungal growth (keep reading for more benefits of lime!).  (Mortars for building and plastering in antiquity)

House windows in first-century Galilee were typically placed relatively high in the wall for maximum ventilation and privacy. Ventilation, as we know, can discourage mold by allowing ions in the fresh air to reach interior surfaces. (Windows)  The same principles were used in design of the homes, which featured a central courtyard with rooms added around it; thus fresh air could flow through the rooms whenever doors were opened to the courtyard. 

Preparing the house for plastering inside requires placing “small chinkstones and mortar to fill cracks and create a flat substrate for the interior plaster. Although obscuring the beautiful view of exposed stone masonry, interior plaster was necessary for insulation and to prevent household pests from taking over.  Plasters also improve interior lighting by brightening up the colours of the walls. We discovered that mixing chalk with the earth plaster gives a bright yet warm tonality to the home. The homes of more wealthy residences and public buildings – such as our synagogue – were finished in white lime plaster and occasionally painted.” (Interior Plaster)

Building techniques in ancient Egypt:  The following facts were taken from the article Homes and Mud-Brick Construction in Ancient Egypt, which references the report by Virginia L. Emery, University of Chicago, UCLA Encyclopedia of Egyptology 2011, escholarship.org:

Unfired mud brick houses were common in ancient Egypt, from the simplest abodes to the grandest of palaces.  Mud brick had several advantages over stone:

• Brick ingredients were available virtually everywhere (sand, clay, and silt combined with chopped straw or dung as temper and binding agent)
• Mud bricks are quicker to fabricate than quarrying stone, making them more economical in that sense
• Mud bricks are quicker and easier to build with because they don’t require the trimming or fitting that building with hewn stone demands. 

“Mud-brick walls could be constructed directly on an unprepared ground surface, though more commonly were provided with brick foundations and wall footings laid in trenches upon a bed of sand... Occasionally, particularly along high- traffic routes, the base of the wall at ground level was protected by a footing of stone, in an effort to minimize the undercutting of the wall due to water or wind damage and traffic; stone elements also could be included in the wall proper, being most common at the quoining of building corners.”

The article Mudbricks give clues to understanding the Bible, which referenced the article Mud Bricks and the Process of Construction in the Middle Bronze Age Southern Levant, confirms that unfired mudbricks are susceptible to water damage.  Water can dissolve the bricks as well as weaken them, especially near the base of the walls. Several strategies are used to help minimize water damage. Typically, the construction techniques in the Ancient Near East involved building a stone foundation of 2-3 courses of stone upon which mudbricks were then placed to the desired height. The stone foundation does two things:  it minimizes the capillary action of water and salts seeping into the lower courses of bricks; it also helps reduce the erosive effect of water splashing from the roof back onto the bricks or from water running in the street.  Another aspect of mudbrick preservation was regular plastering and re-plastering the walls, which helped retard the effects of moisture and erosion, as well as the intrusion of plants, insects, and animals. 

How do these natural building methods defeat mold?

Mud-brick, which is also called adobe in areas of Spanish influence, can still be an economical way to build. Many people think that mud-brick invites mold and dampness into your home, however, it actually inhibits mold in several ways.  Ideal conditions for mold or rot are caused when a building material absorbs moisture and is unable to later release it, or when moisture is not absorbed but condensates on a surface. Here are the ways mud-brick and other earth building techniques inhibit mold, according to Earth Building School:

• Creating thermal mass:  Thermal mass regulates temperature by absorbing heat when it is available, storing it and slowly releasing it when ambient temperatures drop.  Keeping temperatures higher and more constant reduces condensation and dampness, because cold air holds less moisture and so will condensate on windows and walls.Earth is one of the best thermal mass materials available, because of its slow reaction time and because it naturally regulates humidity.  It is easy to retrofit earthen building elements to your existing home: Earthen plaster over drywall, inbuilt cob furniture or mudbrick feature walls - let your imagination run free while creating a beautiful, healthy living space.
• Clay regulates humidity: You can't beat clay when it comes to balancing indoor humidity at optimum levels of 40-60% RH. A solid wall of earth bricks can absorb up to thirty times the moisture of conventional burnt bricks and a 30mm (1-3/16”) thick surface coating of clay is more than enough for daily buffering.  
• Naturally anti-fungal: Finally, natural finishes such as clay, lime plasters or Tadelakt (Moroccan plaster) are naturally anti-fungal.  These are good finishes in areas that are often damp, such as kitchens and bathrooms.  Lime is highly alkaline (high pH) and inhibits mold growth. It can be used to fix mold problems in old buildings (once permanent water damage has been remedied) and is a good and very hygienic choice for bathrooms - even in splash areas such as hand basins and showers.  Lime plaster is water resistant and can be applied as Tadelakt, for a totally waterproof result.  Working with lime - especially in situations where waterproofing is required - is a bit more technical, so it is advisable to get a skilled person onto the job. 

Whether the building is constructed with mud-brick or stone, these are the “bones” of the walls; plaster is placed over the brick or stone, and then the final interior and exterior finishes give them the protective “skin” that really preserve the construction from the elements.  Let’s dive into the finishes of Limewash and Tadelakt to find out why they are so good at inhibiting mold.

Limewash:  This ancient paint has so many physical benefits, and topping it off, has a soft and warming aesthetic that is causing a resurgence in its popularity.  Chemically, limewash is calcium hydroxide mixed with water.  Calcium hydroxide, also known as quicklime, is a naturally-occurring mineral that is soft and easy to mine from the ground (nature also “excavates” lime deposits with water, producing caves with fantastic formations inside).   Adding just the right amount of water causes the mixture to heat up (an exothermic reaction) that can be used immediately or left to cool down and thinned out with more water.  Here are some benefits of applying limewash in your interior or exterior finishes:

• Limewash applied to stone and wood prevents rot and erosion while allowing the structure to “breathe” and release moisture.
• Limewash is a natural pest repellent: the active ingredient, calcium hydroxide, discourages many types of worms, beetles and even mosquitoes from infesting the structure.
• Lime is a farmer’s friend because it naturally deodorizes.  Lime provides free calcium ions, which react and form complexes with odorous sulfur species such as hydrogen sulfide and organic mercaptans found in animal and biological waste.  Thus, waste odors are not “covered over” with lime, but actually destroyed.  (Uses of Lime/Environmental/Animal Waste)
• The high pH of limewash (10-13) makes it anti-fungal, anti-viral and anti-bacterial when it’s wet.  When dry, the pH lowers to neutral; however certain commercial limewashes like Lime Prime by Earthpaint have proprietary resins/polymers that allow the active ingredients to rehydrate and raise the pH again, so that it continually fights mold.
• Limewash (and the plaster beneath it) are naturally incombustible.  This property was recognized at least as far back as 1212, when the King of England decreed that buildings that survived the terrible London fire must be plastered and limewashed immediately to prevent future fires.
• Limewash prevents rust on iron surfaces.  This makes it even easier to apply, as masking off hardware is not necessary unless for aesthetic purposes.
• Limewash is cheap and easy to make on your own.  You’ll just need to purchase calcium oxide (also called burnt lime or quicklime) from a supplier, and be sure to wear the proper clothing and protective gear to guard against chemical burns.  There is plenty of tutorials online, and this article from a long-established UK building conservation company also describes the process.
• Finally, if you prefer skip the DIY and use commercially prepared limewash, Earthpaint, a company that prides itself in only offering non-toxic paints and wood finishes, has a set of products that can specifically tackle damp areas and mold remediation areas: Lime Prime and Lime Seal.  These are also great on unprimed drywall in any location.

Tadelakt: Sometimes referred to as Moroccan plaster, tadelakt is a traditional plaster indigenous to the Marrakesh region of Morocco that can be used as a stylish wall covering and alternative to tiles. It can be used indoors and on exterior walls.  Tadelakt-plastered walls create a solid, waterproof surface that is seamless, has no grout lines and is resistant to mold, which are some of the reasons why this traditional plaster style has become so popular in contemporary, minimalist homes. (Tadelakt: What you Need to Know About Moroccan Plaster)

Tadelakt is applied in several coats and finished using a special technique. "The final stage of polishing is done by using a plastic trowel, Japanese trowel or a traditional Moroccan application which requires a special polishing stone," explains Ian Kozlowski, Founder of Decor Tadelakt.  It's the final stage of applying tadelakt that makes the resulting surface waterproof.  Valentin Tatanov, manager at Tadelakt London explains: "The olive oil soap that is rubbed into the surface of the product chemically reacts with the lime to form calcium stearate."

This waterproof membrane makes Tadelakt appropriate for use in shower enclosures and wet room ideas (where shower walls are not necessary and the entire room can be wetted and drained).  The seamless application means that details like benches, windowsills and shower niches are easy to create.

Tadelakt is relatively low maintenance;  it can be cleaned simply by rinsing with water because the surface resists dirt and mold. "In the shower, squeegeeing down the walls after each shower is all that is needed to maintain the tadelakt shower walls," explains Decor Tadelakt's Ian Kozlowski.  What's even better from a non-toxic standpoint, you must avoid using commercial bathroom cleaners on tadelakt, especially any containing bleach or harsh solvents, as this may destroy its waterproof quality. 

Just like a wooden countertop or cutting board needs periodic maintenance to keep it looking great, water-resistant and bacteria free, "regular recoating with soap solution ensures that the tadelakt stays in excellent condition for years to come," suggests Valentin. 

Shikkui Plaster:  The Japanese started using this type of thick plaster in the 6th century following the spread of Buddhism from the Korean peninsula.  It is made of slaked lime additives including seaweed extracts, soybean oil, natural plant fibers, and eggshells.  It is also used on interior and exterior surfaces.  According to this article, some versions of the plaster also contain plankton skeletons and special algae only found in Japan, which is hygroscopic and helps control humidity. Due to these ingredients and the plaster’s natural ability to absorb pollutants and VOC gasses, it creates healthy airflow within spaces. It is fire and earthquake resistant, has the ability to naturally control bacteria, fungi, and molds; and is naturally anti-static, which reduces dust accumulation.   This Shikkui plaster manufacturer shows the tools and techniques for applying this plaster to practically any wall surface (even wallpaper!).  It is applied quickly in two thin coats back to back, and has a highly polished finish.

For all of their benefits and non-toxicity, we shouldn't be afraid to experiment with limewash, tadelakt and even Shikkui plaster in our homes as the "new" anti-microbial coatings.  They've stood the test of time!