Concrete flooring

wood floorsApplications for system

  • Floor slabs. Can be a skim coat finish floor or a finish can be applied to a slab that is serving a structural role.

Basic materials

  • Portland cement
  • Aggregate
  • Admixtures (including slag, fly ash and other pozzolans to offset portland cement content)
  • Metal reinforcing mesh and/or reinforcement fibers
  • Pigment (can be dispersed through concrete or used as a surface treatment)
  • Sealants and/or finishes

How the system works

Concrete is a mixture of portand cement, aggregate and admixtures. Most slab floors are made from ready-mixed concrete, which is prepared at a batching plant and delivered to the building site mixed and ready to pour. Smaller slabs can be made by site-mixing the ingredients with water. In both cases, formwork is created to shape the slab, filled with wet concrete and leveled. As the concrete sets (a chemical process, not a matter of drying) several stages of finishing occur as the concrete stiffens.

Slab floor. Some buildings will be designed to have a concrete slab floor, and in these cases the most sustainable choice for flooring may be to use the concrete surface as the finished floor.

Concrete slab being laid.

  1. Large slab areas are difficult to install for beginners. From creating and properly bracing forms to mixing, laying and finishing, there is a lot to know before pouring your own concrete. There is a lot of good resource information about working with concrete; research well before proceeding.

Concrete Skim Floor. In some cases, concrete may be applied over an existing sub-floor in a relatively thin layer to provide a finished floor surface. Often, this is done as a means of covering hydronic tubing for radiant floor heating systems built on joist floors.

Concrete can be finished to a wide variety of surfaces, from roughly textured to highly polished. Concrete surfaces can also be stamped in a wide variety of patterns, using rubber mats with the pattern molded in that are applied to the surface when the concrete is still soft. Choices about surface texture will be based on practicality (slippery vs. grippy), aesthetic preferences and the skill and ability of the concrete finisher. It should be made clear to the person in charge of doing the concrete work if the surface is intended to be the finished surface.

Concrete can be poured with pigment mixed in, or the pigment may be cast onto the wet surface of the slab and worked into the concrete during finishing. Concrete can also be poured and finished with no color, or have a color finish applied to the surface after the slab is cured. Some homeowners may choose to have the natural color of the concrete be the finish, whether unsealed or sealed.

Tips for successful installation

  1. To minimize environmental impacts, be sure to specify a concrete mix with the highest possible amount of portland cement replacement material (such as slag or fly ash) and recycled aggregate (crushed concrete). It may take some research to find a batching plant and a concrete finisher willing to do this.
  2. Plan for the type of finish desired prior to ordering and installing the concrete. Be sure both the batching plant and the finisher understand the intent and tailor the mix and their finishing efforts to suit. This is especially the case if using pigments in the concrete or on the surface.

Harvesting — Moderate to High. Portland cement and aggregate ingredients are non-renewable but abundant resources that are widely available. They are quarried or dug from geological deposits. Most limestone quarries have been long established, so are not responsible for the disturbance of untouched ecosystems. Impact at existing quarries tends to be low, and can include interference with and silting of ground and surface water and the creation of airborne dust. Little to no contaminated effluent is created and no chemicals are used in obtaining these materials. Pressure for ever-increasing quantities of aggregate means new pits are being opened, usually close to urban centers and often on or near prime agricultural lands, resulting in serious impacts including loss of arable land, natural habitat disturbance and contamination of ground and surface water.

The balance of materials required for concrete are mainly mined or quarried (including gypsum, calcium sulfate and bauxite, among others), and make up a very small percentage of the mix. These will all have harvesting impacts similar to other quarried materials.

Mining ore to make steel for reinforcement bars or mesh is a high-intensity activity, resulting in serious impacts including habitat destruction and air and water pollution. Depending on the specifications for the slab, the amount of steel used can be low to high.

Manufacturing — High. Portland cement is made by crushing the raw limestone and heating it in a kiln to a high temperature (1300-1500°C / 2350- 2750°F). This is an energy-intensive process and uses fuels such as natural gas, oil, coal and landfill waste, with resulting air and water pollution and habitat destruction. During the heating process, the limestone releases a large amount of carbon dioxide, contributing significantly to greenhouse gas emissions.

Aggregate is relatively low in manufacturing energy inputs and resulting effects.

Admixtures for concrete are often industrial by-products, like blast furnace slag (from ore smelting) and fly ash (from coal burning). While these activities have high impacts, the by-products are not typically attributed with the effects.

The making of steel for reinforcement bars and mesh is a high-intensity activity, including high-energy inputs for melting ore. Impacts include significant air and water pollution.

Transportation — Moderate to High. Sample building uses 5,664 – 14,047 kg of concrete flooring:

5.3 – 21.3 MJ per km by 35 ton truck

Most of the processes involved in making concrete happen relatively close to the source of raw materials, to minimize transportation costs for these heavy materials. Distances from point of harvesting to batching plant may be small or large, depending on the region.

Steel for reinforcement will have varying transportation impacts, depending on the origin of the steel and the number of steps it takes from manufacture to site delivery.

WASTE: Low

Compostable — Excess concrete. Can be left in the environment if crushed into aggregate. Quantities can vary depending on the accuracy of the material take-off for ordering.

Landfill — Excess concrete. Bags from site-mixed concrete ingredients. Quantities can vary from low to high.

ENERGY EFFICIENCY

A concrete floor will have little impact on energy efficiency. When used as a slab floor on grade, an adequate amount of insulation must be used to isolate the slab from cold ground temperatures and in particular any edges of the slab that are exposed to the cold exterior. A concrete floor is very conductive, and feet in contact with concrete may feel colder than the actual temperature indicates, resulting in higher thermostat settings to maintain comfort levels.

MATERIAL COSTS: MODERATE LABOR INPUT: MODERATE

Pouring a concrete slab is a labor-intensive activity, and includes the construction and bracing of formwork, laying of reinforcement bars and/or mesh, mixing/pouring/leveling of concrete and multiple steps of finishing.

Pouring a thin finished floor will not usually require any formwork to be constructed, eliminating one labor-intensive step.

SKILL LEVEL REQUIRED FOR THE HOMEOWNER Preparation of sub-floor — Moderate to Difficult.

If formwork is needed, carpentry skills will be

required. An aggregate base must be laid, leveled and tamped, then a grid work of reinforcing steel laid. The perimeter of the formwork must be leveled, and all required drains, water lines and electrical conduits installed, braced and leveled.

Skim coat floors will not require as much preparation in terms of formwork, but reinforcement and floor penetrations must still be handled. Installation of floor — Moderate to Difficult. The placement and leveling of wet concrete is a skill that requires some experience to master, and as the size of the pour increases so does the level of difficulty. Creating a level floor requires careful preparation and screeding and troweling skills. Finishing concrete requires an understanding of the stages of the curing process and troweling or power-troweling experience. Concrete has a limited working time due to its chemical curing process, so there is no time for mistakes or slow work.

Finishing of floor — Easy to Difficult. If a homeowner is intending to trowel off the finished surface, it can be difficult to achieve a smooth, even floor. Particular finishes (stamping, pigmenting, high gloss) are very difficult to achieve without prior experience. If a fairly level, fairly smooth surface is acceptable, this can be achieved with a moderate level of difficulty. If the homeowner is only applying a finish treatment to the surface of the concrete, then it is a relatively simple process that typically involves brushing or rolling a product onto the floor surface as per manufacturer’s instructions.

SOURCING/AVAILABILITY: EASY

Concrete and concrete finishing are available in every region. Premixed concrete is ordered from a local batching plant, or ingredients can be ordered from building supply outlets or masonry supply stores. Concrete finishing is a common trade, and competitive quotes should be obtainable in most regions.

DURABILITY: VERY HIGH

A concrete floor can last for at least 100 years, and possibly longer.

CODE COMPLIANCE

A concrete slab must be designed and installed to meet the structural requirements of local codes, which all recognize this type of floor. If the concrete floor is only a finish, the sub-floor will have to be designed to meet the loads imposed by the concrete.

INDOOR AIR QUALITY: HIGH

Cured concrete is quite benign, and will have little effect on IAQ. Some products used to color and seal concrete can be extremely toxic. Acid stains will carry warnings for cancer, reproductive system damage and miscarriages for pregnant women. Sealants are often petrochemical based, and many off-gas dangerously in the short and/or long term. Using third-party certified finishes will help to ensure minimal impacts on IAQ.

FUTURE DEVELOPMENT

There is a lot of R&D work into making more environmentally friendly concrete. Currently, concrete manufacturers tout the long life span of concrete as an adequate offset for its high environmental impacts, but this is difficult to support in any balanced analysis. Before concrete becomes a sustainable choice, the high energy inputs and high greenhouse gas emissions must be addressed. While it is likely that developments in these regards will occur, for now the best argument for concrete is in its combined use as a structural floor material and a finished floor. By reducing the need for additional flooring materials, some of its impacts may be balanced. Should it become feasible to create a concrete with much lower impacts that can still serve the double functions of structure and finish, it would be a revolutionary development.

Chapter title page photo credits. Top left to right.

Surface finishing materials

THERE IS A WIDE RANGE OF SURFACES in a building that require a surface finish to protect the material and/or add an aesthetic dimension to the material. Even a small home may have thousands of square feet of surfaces that require treatment, and choices in finishes visually define the building as well as influence longevity. It is rare that one type or one color of finish is chosen for the whole home, leading to multiple finishing decisions that must all work together, both aesthetically and practically.

In many cases, the surface finish is a key element in the durability of the material it is protecting. We ask a lot of our finishes, which take the brunt of exposure to the elements, wear and tear and cleaning. Modern science has succeeded in creating finishing products that offer excellent durability, color choice and fastness, ease of application and adhesion. Unfortunately, in the pursuit of such qualities these products have become proprietary chemical soups. Even the “greenest” petrochemical finishes rely on extraction and manufacture of chemical components that have a wide variety of problematic environmental impacts. There have been excellent developments in reducing the impacts on the end user of such products, but this does not take into account impacts that happen throughout the entire chain of production.

The majority of the finishes described in this chapter fit under the heading of “natural finishes.” They use naturally occurring and minimally processed ingredients that are entirely free of petrochemical products. They are viable on a wide range of surfaces and materials, and offer low impacts and low or no toxins from raw material acquisition through to final application. In some cases, the products may not offer quite the same degree of color choice and fastness, ease of application, durability and adhesion as their petrochemical counterparts; a small trade-off for vastly reduced environmental impacts. And in many cases, the natural finishes offer a beauty and richness that cannot be matched by petrochemical finishes.

The one exception to the focus on all-natural finishes is the section on nontoxic latex paints. While almost every paint company offers a low- or no-VOC version of their latex paint, this alone is not enough to warrant inclusion in this book. These paints may not emit volatile organic compounds, but they still include many dangerous substances, many of which are known carcinogens, endocrine disruptors or other health-adverse chemicals. These can include (but are not limited to): ethyl acrylate, zinc pyrithione, ben- zisothiazolin, triclosan, methylchloroisothiazolin, hexanoic acid, tetraethylene glycol, nepheline syenite, ethylene-vinyl acetate and an array of antimicrobials. There are a few paint companies making an attempt to create actual nontoxic latex paints, and while these are a vast improvement over petrochemical paints of the past, even they are not entirely clean and free of toxins, nor can the chain of production be guaranteed to be clean and nontoxic. However, in the hope of increasing interest in truly nontoxic latex paints, we include them as a category in this chapter. They will offer homeowners the same level of performance expected from commercial paints with greatly lowered impacts.

Building science basics for finishes

Surface finishes can alter the moisture-handling characteristics of the materials to which they are applied, and this is an important building science consideration when selecting finishes.

We often desire a finish that is “waterproof,” and for good reason. If a finish can completely repel all liquid water from penetrating the material it is protecting, the life span of that material can theoretically be extended. However, a truly waterproof coating can often cause as many moisture problems as it alleviates. Moisture will inevitably penetrate building materials; even the best waterproof coating can only delay the process. Depending on the position of the material on the building, restricting the passage of water can also prevent the passage of vapor, robbing the material of the ability to dry out properly and perhaps causing moisture to accumulate in the material or in adjacent materials, causing more harm than a porous finish might suffer.

As an example, a coat of latex paint on the exterior plaster skin of a permeable natural wall system will cause moisture that would have harmlessly passed through the wall and been released to the atmosphere to be trapped in the wall, first saturating the plaster and then the material behind the plaster. Rot and mold will follow.

The most versatile coatings are those that discourage the entry of bulk water via a very tight pore structure, but that still have pores to allow vapor to pass through the finish. This ability to allow moisture to transpire is measured in “perms,” and many finishes have published perm ratings. Many natural finishes do not necessarily have quantified perm ratings, but we can extrapolate from successful applications in a wide variety of climates and over long periods of time that they have a range of permeability that is suitable for long-term durability.

It is never a good strategy to rely on a finish to do a job that the material it is covering cannot do, at least to some reasonable degree, on its own. Finishes should be an enhancement, but not an integral part of, a building science strategy. Paints should not be considered a primary air or vapor control layer, and should not be relied upon to make otherwise vulnerable materials “durable.”

FINISHES

Accurate data for the embodied energy of finish materials is not widely available or consistent between sources. Gross quantities of finishing materials also tend to be small, and many are mixtures of numerous materials that must each be quantified, making accurate embodied energy figures too uncertain to be valuable or meaningful — so they are not included.

Extrapolations for comparison purposes can be made by examining the harvesting and manufacturing impacts listed for each finish.

CODE COMPLIANCE AND FINISHES

Building codes will rarely prescribe finishes for residential construction, except in rare cases in which a particular finish is required by a material in order to be successfully used in a building. For this reason, code compliance is not rated for the products in this chapter.

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