Flooring: MATERIALS ENCYcLOPEDIA
Applications for this system
Finished flooring. Suitable for installation over wet-poured floor and wooden floor systems
Clay, sand and gravel aggregate. Clay floors tend to refer to those that are made with commercially prepared clay and aggregate, while earthen floors refer to those based on naturally occurring site soils that contain an appropriate mix of clay and aggregate. The terms are often used interchangeably.
Admixtures, including flour paste, casein, hydrated lime, blood and other regional formulations
Fiber, including chopped straw, hemp, poly fiber
Pigments, if desired
Finish Material Options:
– Natural oils, including linseed, hemp, tung and walnut oil
– Natural wax (usually applied over oil finishes)
– Commercial floor finishing products (see Chapter 7: Surface Finishing Materials)
Ratings Chart for Earthen floors
The ratings chart shows comparative performance in each criteria category. Click on the tabs below for detailed analysis of each criteria.
- HOW THE SYSTEM WORKS
- ENVIRONMENTAL IMPACTS
- EMBODIED CARBON
- ENERGY EFFICIENCY
- MATERIAL COSTS
- LABOUR INPUT
- SKILL LEVEL REQUIRED
- SOURCING & AVAILABILITY
- CODE COMPLIANCE
- INDOOR AIR QUALITY
- FUTURE DEVELOPMENT
Earthen floor System
People have used earthen floors in their dwellings since we first started making shelters. They have ranged from the soil that was already underfoot to well-mixed and finely finished clay floors. There is certainly a long history to draw upon when considering earthen floors, and many examples of very durable floors. The experience of walking on a well-made clay floor often convinces homeowners they want one!
A clay or earthen floor requires a very stable sub-floor base, as too much flex in the sub-floor may cause the finished floor to crack. Any type of sub-flooring can work, as long as it is constructed to minimize or eliminate deflection under typical conditions.
An appropriate mixture of clay, aggregate and water (along with any admixtures, fiber and/or pigments) are mixed to the desired consistency and poured onto the sub-floor. The material is worked to the desired level and surface texture, usually with trowels. The thickness of this type of flooring can vary greatly, from a thin skim coat to as much as 150 mm (6 inches), though with thick floors it is common to do a thin finish coat separately. In general, the final finished floor is applied between 12–25 mm (1/2–1 inch).
The final surface texture may be achieved during the initial installation, but it is more common to re-trowel the surface at least one time as the floor begins to dry. Some clay floor installers will trowel or rub in a very fine clay mixture at this stage.
Once the desired surface texture has been achieved, the floor is allowed to dry fully (from one week to several months, depending on thickness and climatic conditions). A clay floor must be protected from wear while it is drying. It may be left untouched, or may be covered or planked if work must continue around it.
With the floor suitably dry, the surface treatment is applied. This can range from cold or hot oil applications, waxes or commercial floor-finishing products. Number of coats and time between applications will vary based on the type of treatment used. Natural oils are usually applied in numerous coats, until the floor reaches saturation. Commercial products will have manufacturer’s instructions to guide their application.
Environmental Impact Rating
Harvesting — Negligible to Low
The basic clay and aggregate materials are widely available in many regions, and small-scale extraction has minimal impacts. If sub-soil conditions on-site are suitable for making the floor, enough material is likely to be extracted in preparing the foundation. You may be able to be find small quantities of suitable material from local excavators or at local stone quarries. When manufactured clay and aggregates are used, impacts go up slightly, but commercial extraction is not a toxic process, though it will disturb the immediate ecosystem. Long-established clay pits and aggregate quarries are common, and local ecosystems will have adapted to their presence in many cases.
The finishing products can have a wide variation in impact. Carefully research the origins of “natural” oils, as they can range from locally and organically produced to GMO, factory-farmed oils with toxic chemical additives (in particular, “double-boiled” linseed oil is a highly toxic product). Raw oils are preferable. Waxes, too, can range in impact from locally sourced beeswax to petrochemical wax products.
If you choose commercial finish products, find out what is in them and where they are made to help you assess their environmental impacts.
Manufacturing — Negligible to Low
Processing dry, bagged clay products is a relatively low-energy and nontoxic process, as is aggregate extraction. Clay floors do not require intensive processing. All mixing is typically done on-site by hand or small mechanical mixer. If dry ingredients are being mixed, breathing protection should be worn as airborne silica and other mineral dusts are dangerous to inhale. There are no toxic by-products created during the mixing process.
The manufacturing processes for finishing products vary widely in impact, ranging from low-impact, cold pressing of oil to high-impact petrochemical mixtures.
Transportation — Negligible to Moderate
Sample building uses 1,927.5 kg of clay flooring:
2.9 MJ per km by 15 ton truck
1.8 MJ per km by 35 ton truck
Clay floor ingredients are heavy, and moving them over long distances incurs large transportation impacts. However, most regions will have accessible ingredients within a reasonable radius.
Finishing products are used in quite small quantities and will not incur significant impacts even if they travel long distances, though it’s always preferable to source locally when possible.
Installation — Negligible
Compostable — All leftover clay floor mix can be left in the environment on-site. Quantities will tend to be minimal, as small-batch mixes are the norm.
Recyclable — Containers of finishing products, unless disallowed by recycling programs. Quantities will be minimal.
Landfill — Containers of finishing products if not recyclable. Quantities minimal.
Toxic Waste — Remnants and containers of finishing products if labeled toxic. Quantities minimal.
Chart of Embodied energy & carbon
A clay floor will not have a direct impact on energy efficiency.
Material costs: Low
Mixes using local clay soils will be very low cost, while those using dried, bagged clay will cost more but still be at the low end of the spectrum.
Labour Input: moderate
A clay floor has a similar degree of labor input to other flooring options, though the labor is likely to be spread out over a longer period of time to allow for drying of floor mixes and finishing products.
Skill level required for homeowners
Preparation of sub-floor — Easy
If the sub-floor is suitable stiff, very little needs to be done in advance of pouring the floor. Mesh or fasteners are sometimes used to reinforce the floor and minimize movement.
Installation of floor — Moderate to Difficult
Once a suitable mix has been established, the mixing process is straightforward and the equipment simple to operate. Laying the floor requires some basic understanding of leveling and troweling wet mixtures (similar to working with concrete or plasters), with undulating surfaces being easy to achieve and perfectly smooth and flat surfaces requiring more practice.
Finishing of floor — Easy
Finishing products are generally easy to apply, being brushed or rolled onto the floor and sometimes wiped back with a cloth.
Sourcing & availability: moderate
While the raw materials needed to make a clay floor are widely available, they may not come from conventional building supply sources. Clay soils, if not evident on the building site, can be located locally by talking with excavators and/or aggregate pit operators. Bagged clay is easiest to source from pottery supply outlets. The finishing products may need to be sourced from specialty suppliers.
Each clay floor is made with a custom mix of ingredients, installed with varying techniques and degrees of experience and finished with different products, so durability can range from low to high. Well-mixed, -applied and -finished clay floors can match the durability of commercial flooring options, with a lifespan of ten to forty years. Depending on the type of finish used, maintenance may be required at intervals between one to five years.
Most codes are not prescriptive when it comes to finished flooring materials, as long as the sub-floor has been constructed to code and in a manner intended to support the dead load imposed by the flooring. While it may raise eyebrows, it is unlikely that there will be code restrictions against installing a clay finshed floor.
Indoor air quality: high
The clay floor itself will only have a negative impact on IAQ if the soil, clay and/or aggregate contain toxins. This can happen if the ingredients happen to come from a contaminated source, with contaminants ranging from naturally occurring substances like radon gas and arsenic to those resulting from human activities, like gasoline and oil. These contaminants can be wide-ranging and difficult to detect. Samples can be sent to a laboratory if research into sources shows reason for concern. In general, clay floor ingredients are quite inert and unlikely to be problematic, but shouldn’t be assumed to be so.
The larger IAQ impact is likely to come from the finishing products. Even natural finishes can have high levels of VOCs and other contaminants. Linseed oil, in particular, is a common finish used on clay floors and can have impacts ranging from long-lasting odor to heavy metals from “double-boiled” products. Homeowners with allergies should be certain that any oil product does not cause a reaction before applying it to the floor. Commercial finishing products meeting Greenguard or similar certification will have reliably low impacts on air quality.
Resources for further research
Clay floors are a remarkably environmentally friendly option, with a great deal of potential for development. It would not require very much R&D to be able to formulate reliable clay floor mixes from bagged clay and manufactured aggregates, and the equipment required to harvest, mix and deliver such a product already exists to serve other industries, such as the concrete industry. It would be wonderful to see creative and forward-thinking builders and manufacturers move in this direction, helping to create a wider market for this low-impact, low-cost, no-waste flooring option. Only consumer demand will drive this movement.
Tips for a successful earthen floor
1. While earthen floors have a long and proven history, they are not common in modern construction. Enough excellent examples exist to prove their feasibility, but they are rare enough that anyone choosing this type of flooring is definitely an “early adopter” engaging in an experiment. With proper research and construction, a clay floor is a low-risk experiment, but must be approached with awareness that a successful floor is not guaranteed.
2. Be sure that the construction schedule allows for the drying times required for clay floors. These can range from a week to a month, during which it is best to avoid all traffic on the floor surface.
3. The sourcing of materials for a clay floor is critical, and finding appropriate ingredients will be up to the homeowner and/or installer. Off-the-shelf clay floor mixes are next to non-existent (see Claylin sidebar).
4. Unless the installer is experienced, it is best to create test samples, made on the same type of base as the intended sub-floor and at the intended thickness. Different clay type, aggregate grading and quantities of admixture can have very different results. Time spent refining the formulation will help to achieve a beautiful, durable finished floor.
5. The knowledge base for how to pour, level and trowel a concrete floor can be useful to a clay floor builder. The two materials share enough commonalities that a person capable of working concrete can usually figure out how to work a clay floor.
6. Finishing a clay floor properly is as important as getting the mix right and laying it well. A good deal of the durability comes from the finish, and achieving best results here can take some experimentation.
7. In northern climates, clay floors and finishes are not appropriate for entryways, where wet and salty boot traffic will be problematic for natural oil finishes.
8. North Americans tend to be obsessed with perfectly flat floors, and while clay floors can be made perfectly flat they are an excellent medium for introducing gentle undulations underfoot, to which many people take an instant liking.