Flooring: MATERIALS ENCYcLOPEDIA
Applications for this 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.
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
Ratings Chart for Concrete flooring
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
concrete floor System
Concrete is a mixture of portland 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.
Some buildings will be designed to have a concrete slab floor (see sidebar on concrete, page XXX), and in these cases the most sustainable choice for flooring may be to use the concrete surface as the finished floor.
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.
Environmental Impact Rating
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 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.
Installation — Moderate to High
The mixing and delivery of cement involves mechanical mixing equipment, with the delivery truck typically doing the mixing as it travels to the site. Some installations require the use of pumper trucks, adding to the impacts. Finishing equipment is often gasoline-powered, further adding to impacts.
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.
Chart of Embodied energy & carbon
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
Labour 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 homeowners
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 a hundred years, and possibly longer.
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.
Resources for further research
There is a lot of R&D work into making more environmentally friendly concrete. Currently, concrete manufacturers tout the long lifespan 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.
Tips for a successful concrete floor
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.
3. 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.