Textured exterior surface treatment

A lightweight synthetic stucco composition is disclosed which includes a mixture comprising a latex emulsion, water and titanium dioxide as well as a number of additives for adjusting the properties of the mixture and further including an admixture of hollow microspheres and macrospheres, with the microspheres having a diameter of about 10 to 150 microns and the macrospheres having a diameter of from 300 to 2000 microns, the admixture comprising between 30 and 60% of the finished composition. Utilizing a mixture of microspheres and macrospheres produces a substantial weight savings which makes the synthetic stucco composition easier to apply, less costly to transport and less demanding on the structure of the building. In addition, the particular combination of spherical structures provides a uniform tightly knit appearance free of pinholes and craters as the smaller particles fill the void spaces between the larger ones with the spherical shape of the particles allowing them to pack in a very tight arrangement. Where it is desired to have a more textured appearance, between 1 to 25% by weight coarse silica sand may be added to the admixture, with the coarse silica sand having a particle size from 1500 to 2000 microns.

TECHNICAL FIELD 
This invention relates to surface coating compositions and more 
particularly to lightweight trowelable synthetic stucco surface coatings. 
BACKGROUND OF THE INVENTION 
Synthetic wall coatings for new construction and renovation generally 
utilize the application of a synthetic coating to the exterior of a 
building which is easily applied and manipulated to produce an attractive 
outer surface. A synthetic stucco composition which is trowel applied is 
particularly preferred to produce a decorative wall coating of a desired 
texture. Such a synthetic stucco material is generally used in energy 
saving composite wall systems or may be used as a finish over existing 
masonry walls. Such stucco-type compositions usually include a latex 
binder combined with various fillers and additives such as pigments. Such 
stucco coatings may be used to insulate and waterproof, as well as to 
decorate, the exterior of buildings. 
Generally, silica sand is used as the filler, comprising up to 60% of the 
stucco composition. Such silica usually includes a trace amount of tramp 
iron which, over time, bleeds through the applied coating, causing streaks 
or discoloration. In addition, silica sand is heavy, adding substantial 
weight to the compositions, increasing transportation costs and adding to 
the fatigue of workers who must add and work the composition on a wall 
with a trowel. The silica sand is also of non uniform size and shape, 
producing a non-uniform surface texture easily susceptible to cracking. A 
cratered surface is common, even after manipulation with a trowel. 
In U.S. Pat. No. 4,391,647 to Deer et al, a spackling joint compound is 
disclosed for use as a stucco composition. The compound includes a 
proportion of hollow silica particles which have an average diameter of 
from about 25 microns to about 100 microns, and a density of from about 
0.1 gm per cc to about 0.2 gm per cc. About one to five parts by weight of 
hollow-silica particles are added to a base composition. The use of 
hollow-silica particles is said to produce a lighter weight composition 
and provide less trowel drag during application, with improved surface 
leveling characteristics. 
In U.S. Pat. No. 4,171,228 to Lowrey, a pigment composition for a high 
build protective coating is disclosed which includes pigments selected 
from a first group consisting of low density pigments of smooth nodular 
shape having a maximum particle size of 325 microns and a second group 
consisting of pigments having a median particle diameter ranging from 0.5 
to 20 microns and being shaped so that not more than 20% by weight of the 
smaller particles have ratios of any two dimensions exceeding 10. The 
total pigment volume concentration is not less than 40% and the total 
volume of both groups of pigments is not less than 75% of the total volume 
of pigments in the coating material. A blend of both groups contains from 
20 to 95% by volume of the first group of pigments and from 5 to 80% by 
volume of the second group of pigments. 
In U.S. Pat. No. 4,356,037 to Novak, an abrasion resistant coating is 
disclosed which includes a binder having dispersed therein first abrasion 
resistant particles of substantially uniform size and second abrasion 
resistant particles of substantially uniform size, the second particles 
having a diameter of less than 15.4% of the first particles. The use of 
two different sizes of abrasion resistant particles enhances the overall 
resistance of the coating to erosion by contact with various particle 
sized abrasives. 
Although various types of fillers are disclosed for inclusion in base 
compositions for synthetic stucco, the final compositions are typically of 
substantial weight and do not achieve optimum application characteristics, 
particularly where trowel application of a decorative coating is required. 
Consequently, the search continues for synthetic stucco-type compositions 
which include fillers which reduce weight while increasing the ease of 
application. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a stucco-type 
composition which is easily trowelable onto a surface. 
It is another object of the present invention to provide a synthetic stucco 
composition which is very lightweight and easily transportable. 
It is another object of the present invention to provide a synthetic stucco 
composition which produces an essentially uniform surface texture, 
eliminating voids or cracks. 
It is yet another object of the present invention to provide a composition 
which essentially avoids the use of silicon particles as a filler, thereby 
providing an essentially iron free composition which is not susceptible to 
rust or bleed through. 
According to the present invention, a synthetic stucco type composition 
which is trowelable onto a surface is disclosed which comprises a 
latex-based formulation which may include various additives for adjusting 
the properties of the composition such as bactericides, fungicides, 
thickening agents, etc. The composition further includes an admixture of 
microspheres, having a diameter of from about 10 to 150 microns and 
macrospheres, having a diameter of 300 to 2,000 microns, dispersed 
therein. The macrospheres are admixed in a ratio of about 1:1 to about 4:1 
relative to the microspheres, by weight, with the admixture comprising 
from 10-50% by weight of the final composition. 
Utilizing an admixture of microspheres and macrospheres in a synthetic 
stucco composition provides enhanced trowelability while reducing 
substantially the weight of the composition. In addition, the distribution 
of particle sizes contributes to a uniform texture of the synthetic stucco 
finish with the smaller particles filling the void space between the 
larger ones, giving the surface texture a tightly knit appearance free of 
pinholes and craters. Since the particles are more perfectly spherical 
than silica sand, the particles pack into a very tight arrangement. 
Another advantage of such an admixture is that the larger size particles 
control the spread rate and coverage of the synthetic stucco, allowing a 
trowel to float over the surface of the material during application, while 
the small particles are packed. This is achieved quickly and easily by 
first spreading the composition then lightly rubbing the trowel over the 
surface in a circular pattern, thereby moving only a portion of the 
largest particles while packing the smaller particles to provide a uniform 
surface texture. Consequently, the time required to apply a decorative 
coating is reduced, while the appearance is enhanced.

DETAILED DESCRIPTION OF THE INVENTION 
The composition of the present invention includes a base composition which 
may comprise a mixture of acrylic latex emulsion, water, titanium dioxide, 
various defoamers, bactericides, and/or mildewicide/fungicides as well as 
thickeners such as hydroxyethylcellulose. The base composition may also 
include a solvent for the thickener such as ethylene glycol. Generally, 
the ingredients of the base composition are well known in the art for 
producing synthetic stucco compositions. While a particular combination of 
components will be discussed, it will be understood by those skilled in 
the art that various combinations of materials, ingredients, and additives 
can be used to produce a base composition. 
For producing a trowelable stucco material, a key property is the viscosity 
which is required to provide ease of application and formation of the 
decorative shapes. Generally, viscosities on the order of 70,000 cps are 
common, with such viscosities generally achieved through the controlled 
addition of the thickening agent. 
The inventive composition also includes an admixture of microsphere and 
macrosphere fillers in a ratio of 1:1 to 4:1 by weight respectively. The 
microspheres have a diameter of from 10 to 150 microns and the 
macrospheres have a diameter of from 300 to 2000 microns. Generally, the 
smaller size microspheres are preferably composed of glass with the 
macrospheres preferably composed of a ceramic, such as silicon carbide or 
alumina. Generally, about 10 to 50% by weight of the final stucco 
composition is the microsphere/macrosphere admixture, with 30 to 50% 
preferred. The mean diameter ratio of the microspheres to the macrospheres 
is also important to achieving proper packing. Generally, the microsphere 
should be from 16 to 35% of the diameter of the macrospheres to produce an 
optimum coating texture. 
The microsphere preferably have a specific gravity of about 0.5-0.7 with 
the macrospheres having a specific gravity of about 0.5 to 1. 5. Such low 
densities are achieved by utilizing hollow micro spheres such as the 
holloW glass spheres disclosed in U.S Pat. No. 4,171,228 to Lowrey, and 
are available from P.A. Industries and/or by using as macrospheres the 
ceramic spheres including a microporous interior structure such as that 
disclosed in U.S. Pat. No. 4,632,876 to Laird et al, or those disclosed in 
U.S. Pat. No. 4,680,230 to Gibb et al., which are available from 3M. Since 
these spheres are of such low density and comprise such a large percentage 
of the final stucco composition, there is a substantial savings in weight 
over typical synthetic stucco compositions. Generally, conventional stucco 
contains a large percentage of silica sand or other fillers which produce 
a product with a weight of about 14 to 15 pounds per gallon. Utilizing the 
microspheres and macrospheres in an admixture according to the invention 
produces a product with a weight of about 8 to 9 pounds per gallon. This 
is approximately a 35 to 47% reduction in weight, which makes the 
inventive composition easier to use, less costly to transport, and less 
demanding on the structure of the building. 
Where silica is used as a filler, an additional problem is bleed through of 
residual iron which may discolor the stucco after application. While low 
iron silica is available, trace amounts of iron still persist, with the 
traces multiplied by the large quantity of silica used. Eliminating silica 
sand from the composition eliminates this problem of rust or bleed 
through. 
Another advantage of the present invention is that the distribution of 
particles sizes contributes to a reduction in void spaces which could 
otherwise produce pinholes or craters in the synthetic stucco finish. 
Generally, since the particles are all spherically shaped rather than an 
odd mixture of shapes, the particles tend to pack closely into a very 
tight arrangement which provides an exceptionally smooth surface. 
Utilizing the larger particle size of the macrosphere also effectively 
increases the spreadability of the composition, allowing thinner coatings 
to be applied, further reducing the weight of the final coating. The 
larger particle sizes tend to float with a trowel over the surface of the 
material making it easier to apply while at the same time providing ease 
in spreading and shaping the coating into a decorative configuration. 
In another embodiment of the present invention, the composition, including 
the admixture of microspheres and macrospheres, further comprises the 
inclusion of a percentage of coarse silica sand, from about 1 to 25% by 
weight. Rather than being added as a filler, which requires substantially 
more silica sand, this silica sand is added to provide a different texture 
than the material without the silica sand. Generally, the coarse silica 
sand has a particle size of about 1500 to 2000 microns, producing a grainy 
appearance. Utilizing such a smaller percentage of silica substantially 
reduces the potential for bleed through from trace iron. 
A typical formulation including the microsphere and macrosphere admixture 
is disclosed in Table 1. A typical formulation including the admixture as 
well as the coarse silica sand is disclosed in Table 2. 
TABLE 1 
______________________________________ 
Ingredient* Wt. 
______________________________________ 
Acrylic Emulsion 34.8 
Water 5.8 
Titanium Dioxide 11.6 
Defoamer 0.25 
Bacteriacide 0.20 
Mildewcide/Fungicide 
0.20 
Microspheres 11.6 
Macrospheres 34.31 
Hydroxyethyl Cellulose 
0.32 
Ethylene Glycol 0.92 
______________________________________ 
TABLE 2 
______________________________________ 
Ingredient* Wt. 
______________________________________ 
Acrylic Emulsion 29.53 
Water 4.8 
Titanium Dioxide 9.6 
Defoamer 0.25 
Bacteriacide 0.20 
Mildewcide/Fungicide 
0.20 
Microspheres 9.6 
Macrospheres 19.8 
Silica Sand 25.73 
Hydroxyethyl Cellulose 
0.26 
Ethylene Glycol 0.76 
______________________________________ 
*Universal waterbased tints are added to the system to shade the product 
to the desired color. The range of tint added is between [0-4] fluid 
ounces/gal. 
The inventive composition is manufactured using conventional paint 
dispersing equipment such as a Hockmeyer disperser or other similar 
equipment which is able to grind the titanium dioxide to a hegman grind of 
6.. Generally, high-speed dispersion is only necessary to adequately 
disperse the titanium dioxide within the base composition to whiten the 
product. 
To produce the composition of Table 1, an acrylic latex emulsion, such as 
Rhoplex-AC-234, manufactured by Rohm & Haas, is first charged to a mixing 
tank which may be made of mild steel or stainless steel. The other 
ingredients such as water, defoamer, bactericide, fungicide/mildewicide 
and titanium dioxide, are then added and dispersed at high speed for about 
15 to 30 minutes. A grind check is then made and once it shown that at 
least a grind of six is achieved, the disperser is set at low speed and 
the admixture of microspheres and macrospheres is added slowly to the base 
composition. The admixture includes microspheres obtained from P.A. 
Industries (Extendospheres SL-50), and macrospheres obtained from 3M 
Company, Industrial Mineral Products Division (Macrolite ceramic spheres 
ML-3050 and ML-814). Slow addition of the admixture is required to prevent 
any overshearing which could possibly break or fracture the frangible 
hollow spheres. At this point, various pigments or coloring agents may be 
added to tint the batch to a desired shade. After mixing for a period of 
time, for example about 10-15 minutes, a thickener such as 
hydroxyethylcellulose (pre-mixed with a solvent such as ethylene glycol) 
is added to the mixture. For example, 3 lbs of Natiolsol, made by Aqualon, 
Inc , is added to 10 lbs of ethylene glycol, and mixed to uniform 
consistency, prior to addition to the stucco composition. The thickener is 
added last to allow the even distribution of the various components while 
the mixture is at a low viscosity, on the order of about 10 to 15 kcps, 
which allows the batch to achieve a uniform texture and color in a minimum 
amount of time. Enough thickener is added to achieve a viscosity of about 
70 kcps, which is required to produce a trowelable mixture, with the 
viscosity checked by adjusting the temperature to 77.degree.0 F. and using 
a Brookfield viscometer. Where it is desired to have a coarse surface 
finish, a quantity of silica sand is added along with the microsphere and 
macrospheres admixture to ensure uniform distribution through the batch. 
About 1-25% by weight of low iron silica sand having a particle size of 
1500-2000 microns may be added to adjust the surface texture. This is a 
substantial reduction from the 40-60% silica sand required in most 
synthetic stucco formulations, substantially reducing the potential for 
bleed through. 
FIG. 1 shows a microscopic view of a prior art composition. The known 
compositions are irregularly packed, with large gaps between components. 
This can cause surface pinholes and a non-uniform surface texture and 
profile. In contrast, FIG. 2 shows a microscopic view of a composition of 
the invention. The spherical particles permit closer packing, which 
provides a smoother surface that is free of pinholes and crates. 
While this invention is discussed in relation to a trowelable stucco 
composition including a plurality of additives included therein, it will 
be understood by those skilled in the art that any changes in the choice 
or quantity of additives or base composition can be made without varying 
from the scope of the present invention.