Cementitious structural panels have been used in the construction industry to form the interior and exterior walls of residential and/or commercial structures. Typically, the cementitious structural panel has a hardened cement or plaster layer in between layers of a reinforcing or stabilizing material.
Methods of manufacturing such structural panels include casting in specially designed moulds as well as continuous extrusion processes in which the materials are pressed together in the assembly process. These extrusion methods of manufacture are designed for large scale productions which are usually expensive, do not allow for small scale production and cannot be used in remote areas as they need to be near a constant supply of materials.
The methods of manufacture of cementitious structural panels described above allow one to produce a durable wall material which is suitable for construction of both external and internal walls. The cementitious panels have also found applications in interior construction in sections of a building which are exposed to a high relative humidity or water such as floor underboard.
There still remain several drawbacks to this type of panel. Concrete is not a waterproof material and if the panel surface is not waterproofed in some manner it will absorb water at its surface and the absorbed water, at least for typical panels with a thin concrete layer of about 12 mm in thickness, will migrate through the panel and evaporate into the adjacent room or space. Water migration through the panel can wash out soluble salts in the panel and deposit these salts on the panel surface causing efflorescence which affects the appearance of surface of the panel and any coating which was previously applied.
Water migrating through a panel also carries organic materials and deposits them throughout the cross-section of the panel. These organic substances can encourage microbe growth. The growth of microorganisms, once initiated, cannot be easily eliminated and ultimately leads to its gradual deterioration through the gradual loss of the panel's mechanical characteristics, as well as the loss of aesthetic value of the original structure. This process can only be counteracted if water migration is prevented from the moment of panel installation. In order to prevent this migration, cementitious materials require surface protection on the side where microbiological attack may first occur, namely the side which is directly exposed to moisture intrusion. If this protection is not provided, the deposited organic matter will stimulate microorganism growth leading to the previously described loss of mechanical strength and to inferior appearance.
Another important reason for surface waterproofing of such panels is the degradation of the reinforcing material which may be used to improve the strength of the panel. Because of the alkaline nature of cement, the strength of the reinforcing materials can be destroyed over time. Alkaline-resistant coatings may be applied to the reinforcing material but these coatings are not always resistant to microbiological degradation and moreover may not always be effective, as the degradation of the reinforcing material results from the presence of water.
The above concerns are widely shared throughout the construction industry and have resulted in various countermeasures to provide structural panels with waterproof characteristics. For example, urethane elastomers have been sprayed on installed structural panels. Another solution has been to insert a waterproof film into the panel between two layers of concrete material. Alternatively, a sheet made from a thermoplastic resin may be adhered to the surface of the panel. Still others have suggested a silicon rubber sealer composition or a waterproof fibrous plate be used to restrict moisture penetration. Expansive insulating materials have also been used to waterproof and insulate masonry units. Finally, others have attempted to construct an inner layer of concrete, intermediate layer of insulation, and outer waterproofing layer by interconnected hollow passageways, or adhering a rigid layer of insulation or asphalt-elastomer continuing membrane to a cementitious layer by the means of waterproofing adhesive.
Many of the above systems have two disadvantages. The first is that they require a considerable amount of labour. The second is that their performance depends on the skill of the field worker because they are applied at a construction site where only lower precision can be achieved. These systems frequently fail because there is a tendency for contractors to use less than the recommended quantity of material or to use inferior materials since proper materials are generally expensive. In addition, liquid systems have a tendency to settle or separate during storage. If such a system is not properly mixed prior to use, the concentration of active component varies throughout the height of a container in which it is stored causing inconsistent application. Many systems freeze or cannot be applied at certain weather condition which limits field application of these materials. Also, structural panels should be waterproofed immediately after installation to protect them from rain which is not always possible due to work scheduling and uncertain weather conditions.