Surfaces formed of concrete block, brick or poured concrete contain surface imperfections including voids, hairline cracks, poor joints and uneven areas. For aesthetic reasons it would be desirable to apply a coating of paint over these surfaces to fill the voids and leave a protective overcoat. Conventional cement base paints are acceptable for weatherproofing in that they will seal a porous masonry structure but cannot provide a smooth or uniformly thick outer coating. Instead they tend to be absorbed into the structure. On the other hand a conventional latex formulated paint forms a coating which will fill hairline cracks but is much too thin to fill voids and does not adhere well to a cementatious surface. In fact, the thin film formed by conventional latex formulated paint cannot provide a coating of satisfactory smoothness and thickness to plug up the cracks in a cementatious surface even when both a primer and finishing coat is applied. If too heavy a layer of latex paint is applied to the surface, cracking or crazing will occur as the paint cures and the paint will tend to flake and peel after curing. A paint composition which will coat a cementatious surface in a reasonable thickness to cover surface irregularities, voids and defects and which can be uniformly applied to leave a smooth protective outer layer would represent an entirely new architectural tool for the building trades and the homeowner.
In the parlance of the paint industry a paint is a three component system of binder, pigment and diluent. The paint should spread readily and easily as it is applied to a surface yet should have a substantial reluctance to flow under gravity. However, even the most extremely viscous commercially available latex formulated paint is poor in its resistance to flow under gravity. A paint which is thixotropic will come close to providing an ideal physical flow characteristic, i.e., one that is as free flowing as desired during application but is essentially immobile immediately after application. Commercially available latex paint formulations vary widely in viscosity but are essentially Newtonian or non-thixotropic. Thixotropy is the property of a liquid or gel that is characterized by loss of viscosity under stress and by regain of the original viscous state upon removal of the stress. Many conventional aqueous based paints include viscosity additives in their formulation t increase their resistance to flow. However, the degree of thixotropy in such paints is minimal if at all.
It is known to us cement base paints which use portland cement as the binder and principal constituent for application upon masonry surfaces. The portland cement, usually white portland, is combined with lime and usually an accelerator such as calcium chloride to which may be added pigment or coloring agents. The ingredients are mixed and milled to form a dry powder. The dry powder is commercially sold with instructions to mix with water to form a slurry which is applied to the masonry surface as a conventional paint. A conventional cement based paint is, however, nonthixotropic and the use of lime poses environmental dangers and causes efflorescence. Portland cement has also been mixed with nonaqueous organic paint compositions in a attempt to formulate a paint composition for masonry surfaces. Such organic compositions are also nonthixotropic and tend to form coatings which lack cohesiveness and are disposed to cracking and crazing as the paint cures.