Following topics regarding exposed concrete floors are covered:
- Properties of exposed concrete floors
- Applications of exposed concrete floors
- Construction of exposed concrete floors
- Exposed concrete floor finishes
- Pattern and texture of exposed floor finishes
- Color of exposed concrete floor
Fig.1: Exposed Concrete Floors and Finishes
Properties of Exposed Concrete Floors
- Exposed concrete floor needs to be adequately strong to be able to support the heavy load and traffics.
- It should be durable.
- It should properly resist wearing.
Applications of Exposed Concrete Floors
Exposed concrete floors are suitable for various applications and can be considered for many projects. This is because it offers acceptable and satisfactory performance in most cases. The common applications of exposed concrete floors are:
- Domestic living rooms
- It is particularly desirable to be combined with underfloor heating for efficient and continuous heating space heating
Construction of Exposed Concrete Floors
Generally, the prime aim for the construction of exposed concrete floor is to have leveled concrete floor surface, distribute aggregate evenly, and keep air voids to as minimum as possible.
The following procedure should be followed to achieve such objective:
- Concrete should have an adequate compressive strength (minimum 32MPa) and utilization of additives should be prevented.
- The use of agents such as curing agents should be avoided unless it is accepted in advance. This is to prevent chemical reactions which might occur during polishing of concrete floor surface.
- Finished surface tolerances are maximum +/-3mm for the 3m length, +/-2mm for the 1m length, and +/-1mm for the 0.3m length.
- The application of mechanical or hand trowel will not only reduce air voids but also level the surface.
- Edging trowel is advised to be used for finishing exposing edges.
- The casting of aggregate, stones and other objects that intended to be polished should be carried out after screeding and prior to bull floating and troweling.
Finishes for Exposed Concrete Floor
Generally, the upper face of the exposed floor is flat and unformed, unlike others faces which are formed due to formworks. So, the upper face needs to be formed using proper techniques to achieve required texture and shape.
Frequently, polished finishes are considered for exposed concrete floors and two methods are available to achieve this type of floor finish. It should be known that each technique produces different exposed floor appearance.
These polishing techniques are explained in the following sections:
- Power floated method
- Diamond polished method
Power Floated Method of Finishes for Exposed Concrete Floor
Power floated method is carried prior to the full curing and hardening of concrete, so the success of power floated technique is considerably dependent on the time at which the process is started.
Initially, the pan floater is applied to cut the surface of the partially cured concrete and then troweling is used to smoothen the surface.
Commonly, suitable powered tools are used to achieve designated floor finish, but the application of hand trowelling is also acceptable in small spaces. If it is necessary, the higher degree of polishing can be achieved using various sealants.
The color of the polished surface is governed by fine components of the concrete mixture such as cement, sand, and pigments if present.
Diamond Polished Method of Finishes for Exposed Concrete Floor
Diamond grinder is used to polish exposed concrete floor surface. The equipment removes concrete layer whose thickness does not exceed few millimeters at the top of the floor. After that, a fine grade protection layer is applied to provide the favored polished finish.
If the diamond polished method is considered, it would be required to determine cement color, pigment, and type of aggregate to obtain the desired floor finish.
Pattern and Texture of Exposed Floor Finishes
In addition to the polished exposed concrete floor surface, patterns, grains, and textures can be produced through the removal of the top thin layer of concrete. This is specifically beneficial in areas where slip resistance is needed. Consideration of suitable concrete mixture is vital for proper aggregate exposure.
If such special measure is not considered at concrete mix phase, aggregate would not remain close to the concrete surface after compaction which is not desirable in the case of the exposed concrete floor.
There are different methods by which concrete can be removed to get certain texture, pattern and slip resistance. These methods include water blasting, shot blasting, imprinting wet concrete and use of surface retardants and concrete brushing.
In this method, water is applied to remove mortar and expose the aggregate. Time of water blasting process should be specified properly to ensure that concrete gain enough strength to hold coarse aggregate. Water blasting should be carried out by an experienced worker.
In this method, steel balls are forced into concrete to expose aggregate and it is suitable for sand exposure.
Imprinting Wet Concrete
It is an economical method which uses form texture and enhances slip resistance of concrete floor.
Use of Surface Retardants
It is claimed that the use of surface retardant is considerably accurate in exposing the aggregate. In this technique, retardant materials are applied to the concrete floor surface to avoid hardening of the top thin layer of concrete and then remove it through water washing or brushing.
The thickness of concrete intended to be removed is based on the type of retardant material.
This method increases slip resistance of exposed concrete floor surface. It is economical, but uniformity cannot be achieved easily that is why it is suitable for places where aesthetic appearance is not a major concern.
Color of Exposed Concrete Floor
Exposed concrete floor color is controlled by fine grain constituents of concrete mix and the degree of aggregate exposure. However, it is possible to provide certain color to the exposed concrete floor.