Fibrous mat-faced gypsum board in exterior and interior finishing systems for buildings

Gypsum-containing boards, uses for these boards, and methods for making them are provided. The board includes a set gypsum core having a fibrous glass at disposed thereon. The core includes a water-resistant additive in at least a minimum amount sufficient to impart to the board an ASTM C-473 water absorption value of less than about 10%. This additive includes organohydrogenpolysiloxane resin added with a portion of the mixing water, or otherwise added in neat form to the process for preparing the slurry.

FIELD OF THE INVENTION 
The invention described in aforementioned application Ser. No. 583,874 
relates to improvements in exterior finishing systems such as, for 
example, exterior insulation systems for buildings, and also to 
improvements in shaft wall assemblies for buildings. More particularly, 
the aforementioned invention relates to an improved structural component 
for use as a support surface in an exterior finishing system, including an 
exterior insulation system (sometimes referred to herein for convenience 
as "EISystem"), and also to the use of said component in hollow shaft wall 
assemblies, for example, those used in constructing elevator shafts and 
stairwells. 
The EISystem and shaft wall assemblies described in said '874 application 
include as a structural component thereof a fibrous mat-faced gypsum 
board. The claims of said '874 application are direction to said improved 
EISystem, to improved fibrous mat-faced gypsum board which can be used in 
said system, and to the preparation of said improved board. 
Although the present application includes a description of said EISystem 
and of said improved board, the description and claims hereof are directed 
to improved exterior and interior finishing systems which include a 
fibrous mat-faced gypsum board as a structural component thereof. The 
present invention will be described initially in connection with its use 
in roof deck systems and in plaster lath systems, but as will be explained 
hereinafter, its use has wider applicability. 
Installation of an exemplary and popularly used roof deck system in 
construction of a building, including newly constructed buildings, 
generally involves the following sequential steps: (A) constructing a 
frame for support of the roof of a building; (B) affixing to the frame 
corrugated sheets to provide a surface for support of the other components 
of the roof deck system; (C) affixing to the corrugated sheets planar 
support members; and (D) affixing to the planar support members an 
exterior finishing material having good weathering properties. Roof deck 
systems which include panels of insulation sandwiched between the 
aforementioned corrugated sheets and planar support members are used 
widely also. Such systems are designed to be insulative in character and 
weather resistant. Such roof deck systems can be used to advantage to 
conserve energy used for heating and to conserve energy used for 
air-conditioning. 
More specifically, such roof deck systems typically include corrugated 
metal sheets which are mechanically affixed, usually by screws or bolts, 
to appropriate structural members of the building such as steel beams. The 
corrugated metal sheets support the weight of the components which overlie 
it, including the insulating material (when used), the planar support 
members, and the finishing material. Light weight, low density insulating 
panels of expanded polystyrene, are used widely in such systems, 
especially in colder climates. The planar support members generally 
comprise gypsum board and are fastened in place by mechanical fasteners 
such as screws to the underlying corrugated metal sheet. When panels of 
insulation are used, they are sandwiched between the underlying corrugated 
metal sheets and the overlying panels of gypsum board. An exterior 
finishing material, such as a rubber membrane or alternating layers of 
asphalt and roofing felt, overlies the panels of gypsum board. 
Another exemplary roof deck system that is in wide use is one that is known 
as the "poured-in-place" gypsum deck. Construction of such decks usually 
involves the following sequential steps: (A) constructing a frame for 
support of the roof of a building; (B) applying to the frame planar 
support members to provide a surface for support of the other components 
of the system; (C) placing a reinforcing mesh-like material on the support 
members; (D) pouring over the mesh-like material a cementitious slurry 
which hardens to form a smooth continuous deck surface for the support of 
the other components of the system; and (E) affixing to the hardened 
cementitious deck an exterior finishing material having weather -resistant 
properties. 
More specifically, such "poured-in-place" gypsum decks generally comprise 
elongate, horizontally disposed supporting metal I-beams (called 
"purlins") which are attached to appropriate structural members of the 
building. Elongate, horizontally disposed sub-purlins or "bulb Tees", 
so-called because of their resemblance to an inverted "T" when viewed in 
cross section, are positioned transversely across the tops of the 
underlying purlins, and are usually welded into place. The planar support 
members, which typically comprise panels of gypsum board, are laid between 
the sub-purlins and are supported there by flanges formed by the bottom of 
the inverted "T". (Such gypsum board panels are referred to in the 
industry as "form boards".) Open metal mesh reinforcing screen is laid 
over the gypsum form boards and sub-purlins. A gypsum slurry is then 
poured over the screen, sub-purlins and gypsum form boards to a 
predetermined depth. Once the gypsum slurry has set and dried, a roofing 
membrane such as the aforementioned alternating layers of asphalt and 
roofing felt is adhered to the top of the deck. 
It is noted also that the face of the form board facing the interior of the 
building, that is, the ceiling thereof, may be finished with interior 
finishing systems, usually by "field painting" with a suitable form board 
paint. The paint is typically applied under pressure with a sprayer. 
An example of a poured-in-place roof deck is described in U.S. Pat. No. 
3,289,371. This patent refers to the tendency of such decks to crack. This 
weakens the deck and stresses the roofing membrane, thereby inducing roof 
failure and leaking. To combat these problems, the need for a suitable 
support member and proper reinforcement is stressed. 
It is mandatory that roof deck systems, including the types described 
above, possess certain characteristics for commercial acceptability. For 
example, it is particularly important that the planar support members, for 
example, panels of gypsum board, used in such systems possess 
fire-resistant qualities that enable the systems utilizing them to meet 
the strict fire regulations of municipal codes. In addition, it is also 
important that the support members possess water-resistant qualities which 
enable the board to resist the significant weathering which such systems 
are subjected to during both installation and use. Such weathering 
includes, for example, attack by precipitation and wind uplifting, each of 
which contributes to the degradation of the overlying finishing materials 
and the underlying planar support members. 
As regards interior finishing systems for use in a building, installation 
of such a system generally involves the following sequential steps: (A) 
constructing a frame for support of the interior walls of a building; and 
(B) affixing to the frame planar support members which provide a smooth 
continuous surface to support an interior finishing material having 
aesthetic and durability properties. Such systems are designed to be 
strong and durable and to withstand abuse during the building's occupancy. 
More specifically, an exemplary interior finishing system includes: (A) 
wood or metal frame members which are mechanically affixed to appropriate 
structural members of the building; (B) planar support members comprising 
panels of gypsum lath; and (C) "thin coat" or "veneer" plaster covering 
the gypsum lath. The gypsum lath panels are mechanically affixed by nails 
or screws to the frame members. 
The effective application of the plaster coating to the gypsum lath is 
tricky business. Problems often arise because the thin plaster coating 
contains a relatively large quantity of water when applied. Until a 
significant portion of this water is removed from the plaster, it cannot 
be properly smoothed by troweling. Where the removal of water from the 
plaster is primarily by air drying, it has been found that by the time the 
plaster is in a trowelable condition, it is also close to setting, leaving 
insufficient time to do the troweling job properly. For this reason, it 
was once the practice to apply a relatively rough plaster base coat 
followed by a relatively thin plaster finish coating. This practice is 
somewhat self-defeating since the material and labor savings intended to 
be gained with the thin coat plaster are not realized when more than one 
plaster coat is applied. 
If, on the other hand, the water in the plaster coating is withdrawn too 
quickly, as by use of highly water absorbant gypsum lath, the plaster 
coating dries out before it has time to set, this leading to cracking and 
spalling of the set plaster coating. Thus, a balance must be struck such 
that the rate of water absorption from the thin plaster coating applied to 
the planar support surface is sufficiently slow to avoid drying prior to 
setting, yet sufficiently rapid to remove a sufficient quantity of water 
to permit the plaster to be properly troweled. 
The present invention relates to improved exterior finishing systems and to 
improved interior finishing systems, including, for example, roof deck 
systems and plaster lath systems, which include an improved planar support 
member as a structural component thereof. 
REPORTED DEVELOPMENTS 
As mentioned above, widely used roof deck systems include gypsum board as 
the planar support member thereof. Such gypsum board is paper-faced and 
includes a set gypsum core which ordinarily includes therein 
fire-resistant and water-resistant additives, for example, chopped glass 
fibers and wax-asphalt emulsion, respectively. The surface of the paper 
facings of the board are typically treated with a water repellant agent, 
such as, for example, a poly(ethylene) emulsion. The use of such 
water-resistant additives and water repellant paper is designed to provide 
a product that resists attacks by precipitation which is particularly 
damaging during the construction phase of the roof deck system. 
Nevertheless, it has been found that such paper-faced, water-resistant 
gypsum board is usually damaged by exposure to precipitation. The paper 
facing tends to come loose and degrade, and the gypsum core tends to 
deteriorate. Damaged paper facing and a deteriorated core comprise a poor 
substrate upon which to adhere an overlying material such as a roof 
membrane. 
With respect to gypsum lath used commercially in the aforementioned 
interior finishing systems, it comprises also a set gypsum core faced with 
paper. An example of such paper-faced gypsum lath is described in U.S. 
Pat. No. 3,382,636, assigned to the assignee of the present application. 
The gypsum lath comprises a gypsum core having a thickness, for example, 
of about 1/2", sandwiched between sheets of paper which may be coated on 
the side contiguous the core with an adhesive in order to secure the 
product together. On the plaster-receiving side of the lath, there are 
provided small apertures or pinholes which extend through the paper and 
through the adhesive coating (if used). The pinholes of the paper, which 
is treated with a wetting agent, provide passageways for excess water from 
the thin plaster coating applied thereover to pass into the relatively 
absorbent gypsum core. This permits the plaster coating to reach a 
trowelable consistency before setting, leaving sufficient time for a 
worker to do the troweling job properly. 
The gypsum core of the above-described gypsum lath may include chopped 
glass fibers as a reinforcing and fire-resistant additive. In addition, 
such lath may be insulated with, for example, aluminum foil laminated on 
one side of the lath. Examples of such lath and thin coat plasters for use 
therewith are described in Georgia-Pacific publication No. 6695 entitled 
"Plaster Products/Dens-Cote Veneer Lath and Plaster". 
It would be of benefit to have a gypsum lath (also referred to in the 
industry as "veneer lath") which enables the applicator to more readily 
apply the plaster coating and in a manner such that a good finished 
product is obtained consistently. 
In accordance with the present invention, there are provided an improved 
exterior finishing system and an improved interior finishing system, each 
of which include a gypsum based structural component, including for 
example, improved roof decks and interior systems which include thin 
plaster coatings adhered to veneer or gypsum lath. 
SUMMARY OF THE INVENTION 
In accordance with the invention described and claimed in aforementioned 
application Ser. No. 583,874, there is provided an improved structural 
support element comprising a fibrous mat-faced gypsum support surface for 
use in an exterior finishing system, including exterior insulating 
systems, for buildings. A preferred form of the fibrous mat-faced gypsum 
support surface or member described and claimed in said '874 application 
comprises a gypsum core having one or more additives therein which improve 
the water resistance of the core. 
In accordance with the present invention, there is provided an exterior 
finishing system or an interior finishing system for use in a building 
comprising, as a support member thereof, a fibrous mat-faced gypsum board 
comprising a gypsum core having one or more additives therein which 
improve the water resistance of the core, and an exterior or interior 
finishing material overlying said board. 
In preferred form, the mat for use in said invention is a glass fiber mat 
in which filaments of glass fiber are bonded together by an adhesive. 
For use in applications in which fire-resistant properties are deemed to be 
important, said gypsum core includes also one or more additives which 
impart improved fire-resistant properties to the board. 
A particular embodiment of the present invention comprises a roof deck 
system for use in a building which includes supporting means, preferably 
corrugated sheet(s), fibrous mat-faced, water resistant gypsum board 
overlying said means, and an exterior finishing material overlying said 
board. In a modified form of this embodiment, insulating material is 
sandwiched between said supporting means and said gypsum board. 
Another embodiment of the present invention comprises a roof deck system 
comprising a fibrous mat-faced, water-resistant gypsum board, a 
cementitious composition overlying said gypsum board, and an exterior 
finishing material overlying the cementitious composition. In preferred 
form, a mesh-like material is sandwiched between said gypsum board and 
said cementitious composition. 
A particular embodiment of the present invention comprising an interior 
finishing system comprises a plaster lath system which includes a fibrous 
mat-faced, water-resistant gypsum board and an interior finishing material 
overlying said gypsum board. In preferred form, said finishing material 
comprises a mono-ply of thin plaster coating. 
An additional preferred form of the invention described and claimed in the 
'874 application comprises a gypsum board having each of its core faces 
covered with a porous glass fiber mat, with the mat of one of the faces 
being adhered to the core by set gypsum penetrating but part-way into the 
thickness of the mat and having its outer surface substantially free of 
set gypsum. As will be described below, the glass fiber mat surface, which 
is free of set gypsum, provides an excellent substrate to which there can 
be adhered panels of insulation, or exterior finishing materials such as 
asphalt, or interior finishing materials such as plaster. 
There are numerous advantages which flow from the use of the aforementioned 
invention in both exterior and interior finishing systems which include 
fibrous mat-faced, water-resistant gypsum board. Such fibrous mat-faced 
support surfaces that have exterior or interior finishing materials 
applied thereover can have higher tensile or cohesive strength than a like 
system that includes paper-faced gypsum board. The fibrous mat-faced 
surface of the gypsum support element is "nailable", and accordingly, it 
can be secured readily to an underlying frame or other substrate by 
nailing. In comparison to various of the commercially available systems, 
the improved support surface of said invention has improved strength 
uniformity in both the length and width dimensions of the system. Unlike 
conventional paper cover sheets, the fibrous mat does not expand or 
contract during the manufacture of the product; this reduces cockle and 
leads to uniformity of dimensions. The water-resistant board provides a 
substantially improved weather-resistant product which better resists 
degradation both within and outside of the system. The use of 
fire-resistant additive(s) in the core of the board provides a structural 
element that can be used to excellent advantage in the numerous and varied 
applications in which conventional paper-faced gypsum lath is used. Such 
applications include, for example, the use of the board as structural 
components of walls, ceilings, partitions, and the like.

DETAILED DESCRIPTION OF THE INVENTION 
The essential components of the finishing system of the present invention 
comprise fibrous mat-faced, water-resistant gypsum board and an overlying 
finishing material. The finishing material can be in multi-ply or mono-ply 
form. It can be positioned contiguously to said gypsum board or it can 
directly overlie or be directly affixed to a member(s) which is sandwiched 
between said gypsum board and said finishing material. 
Turning first to a description of the fibrous mat-faced, water-resistant 
gypsum board for use in the present invention, it comprises a set gypsum 
core faced with a fibrous mat. The gypsum core is basically of the type 
used in those gypsum structural products which are known as gypsum 
wallboard, dry wall, gypsum board, gypsum lath and gypsum sheathing. The 
core of such a product is formed by mixing water with powdered anhydrous 
calcium sulfate or calcium sulfate hemihydrate (CaSO.sub.4 
.multidot.1/2H.sub.2 O), also known as calcined gypsum; and thereafter 
allowing the mixture to hydrate or set into calcium sulfate dihydrate 
(CaSO.sub.4 2H.sub.2 O), a relatively hard material. The core of the 
product will in general comprise at least about 85 wt. percent of set 
gypsum. 
The composition from which the set gypsum core is made can include optional 
constituents, including, for example, those included conventionally in 
gypsum sheathing. Examples of such constituents include set accelerators, 
retarders, foaming agents, and dispersing agents. As will be described in 
more detail below, a preferred gypsum core for use in exterior and 
interior finishing systems includes one or more additives which improve 
the water resistant properties of the core. 
The surface of the core of the gypsum board is faced with a fibrous mat. 
The fibrous mat should be sufficiently porous to permit water in the 
aqueous gypsum slurry from which the gypsum core is made to evaporate 
therethrough. As described in detail below, the fibrous mat-faced gypsum 
board can be made efficiently by forming an aqueous gypsum slurry which 
contains excess water and placing thereon the fibrous mat. Aided by 
heating, excess water evaporates through the porous mat after the calcined 
gypsum sets. 
The fibrous mat comprises material which is capable of forming a strong 
bond with the set gypsum comprising the core of the gypsum board. Examples 
of such materials include a mineral-type material such as glass fibers and 
synthetic resin fibers. The mat can comprise continuous or discrete 
strands or fibers and be woven or nonwoven in form. Nonwoven mats such as 
chopped strand mat and continuous strand mat can be used satisfactorily 
and are less costly than woven materials. The strands of such mats are 
bonded together by suitable adhesive. The mat can range in thickness, for 
example, from about 15 to about 40 mils, with a thickness of about 25 to 
about 35 mils being preferred. The aforementioned fibrous mats are known 
and are commercially available in many forms. 
The preferred fibrous mat is a fiber glass mat comprising fiber glass 
filaments oriented in random pattern and bound together with a resin 
binder. Fiber glass mats of this type are commercially available, for 
example, those sold under the trademark DURA-GLASS by Manville Building 
Materials Corporation and those sold by Elk Corporation as BUR or shingle 
mat. 
Although improvements can be realized by the use of a gypsum core which has 
but one of its surfaces faced with fibrous mat as described herein, it is 
preferred that both surfaces of the core be faced with substantially the 
same fibrous material. If the surfaces of the core are faced with 
materials that have different coefficients of expansion, the core tends to 
warp. Fibrous mat-faced 
gypsum board and methods for making the same are known, for example, as 
described in Canadian Patent No. 993,779 and U.S. Pat. No. 3,993,822. 
The fibrous mat-faced gypsum board for use in the present invention 
comprises a gypsum core which has water-resistant properties. The 
preferred means for imparting water-resistant properties to the gypsum 
core is to include in the gypsum composition from which the core is made 
one or more additives which improve the ability of the set gypsum 
composition to resist being degraded by water, for example, to resist 
dissolution. In preferred form, the water resistance of the core is such 
that it absorbs less than about 10%, preferably less than about 7.5% and 
most preferably less than about 5% water when tested in accordance with 
ASTM method C-473 with only the edges exposed. 
Fibrous mat-faced gypsum board having a gypsum core which does not have a 
water-resistant additive(s) therein has substantially better 
water-resistant properties than conventional paper-faced gypsum wallboard 
or sheathing. Nevertheless, evaluations have shown that the bond between 
the fibrous mat and gypsum core can deteriorate relatively quickly under 
the influence of water. For example, samples exposed to the weather showed 
loosening at the glass fiber facing within one to two months. In contrast, 
evaluations of water-resistant gypsum core faced with fibrous mat, as 
described herein, have shown the bond between the mat and core resists 
being degraded by water for indefinite periods of time. 
Examples of materials which have been reported as being effective for 
improving the water-resistant properties of gypsum products are the 
following: poly(vinyl alcohol), with or without a minor amount of 
poly(vinyl acetate); metallic resinates; wax or asphalt or mixtures 
thereof; a mixture of wax and/or asphalt and also cornflower and potassium 
permanganate; water insoluble thermoplastic organic materials such as 
petroleum and natural asphalt, coal tar, and thermoplastic synthetic 
resins such as poly(vinyl acetate), poly(vinyl chloride) and a copolymer 
of vinyl acetate and vinyl chloride and acrylic resins; a mixture of metal 
rosin soap, a water soluble alkaline earth metal salt, and residual fuel 
oil; a mixture of petroleum wax in the form of an emulsion and either 
residual fuel oil, pine tar or coal tar; a mixture comprising residual 
fuel oil and rosin; aromatic isocyanates and diisocyanates; 
organohydrogenpolysiloxanes; a wax-asphalt emulsion with or without such 
materials as potassium sulfate, alkali and alkaline earth aluminates, and 
Portland cement; a wax-asphalt emulsion prepared by adding to a blend of 
molten wax and asphalt an oil-soluble, water-dispersing emulsifying agent, 
and admixing the aforementioned with a solution of casein which contains, 
as a dispersing agent, an alkali sulfonate of a polyarylmethylene 
condensation product. 
A preferred material for use in improving the water-resistant properties of 
the gypsum core comprises wax-asphalt emulsion, species of which are 
available commercially. The wax portion of the emulsion is preferably a 
paraffin or microcrystalline wax, but other waxes can be used also. The 
asphalt in general should have a softening point of about 115.degree. F., 
as determined by the ring and ball method. The total amount of wax and 
asphalt in the aqueous emulsion will generally comprise about 50 to 60 wt. 
percent of the aqueous emulsion, with the weight ratio of asphalt to wax 
varying from about 1 to 1 to about 10 to 1. Various methods are known for 
preparing the wax-asphalt emulsion, as reported in U.S. Pat. No. 3,935,021 
to D. R. Greve and E. D. O'Neill, assigned to the same assignee as the 
present invention. Commercially available wax asphalt emulsions that can 
be used in the composition described herein are sold by United States 
Gypsum Co. (Wax Emulsion), Monsey Products, (No. 52 Emulsion) and Douglas 
Oil Co. (Docal No. 1034). The amount of wax-asphalt emulsion used can be 
within the range of about 3 to about 10 wt. percent, preferably about 5 to 
about 7 wt. percent, based on the total weight of the ingredients of the 
composition from which the set gypsum core is made, said ingredients 
including the water of the wax-asphalt emulsion, but not including 
additional amounts of water that are added to the gypsum composition for 
forming an aqueous slurry thereof. 
A particularly preferred material for use in improving the water-resistant 
properties of the gypsum core comprises a mixture of materials, namely, 
poly(vinyl alcohol) and wax-asphalt emulsion of the aformentioned type. 
The use of such additives to improve the water resistance of gypsum 
products is described in aforementioned U.S. Pat. No. 3,935,021. 
The source of the poly(vinyl alcohol) is preferably a substantially 
completely hydrolyzed form of poly(vinyl acetate), that is, about 97 to 
100% hydrolyzed polyvinyl acetate. The poly(vinyl alcohol) should be 
cold-water insoluble and soluble in water at elevated temperatures, for 
example, at temperatures of about 140.degree. to about 205.degree. F. In 
general, a 4 wt. percent water solution of poly(vinyl alcohol) at 
20.degree. C. will have a viscosity of about 25 to 70 cp as determined by 
means of the Hoeppler falling ball method. Commercially available 
poly(vinyl alcohols) for use in the composition of the present invention 
are available from E. I. Du Pont de Nemours and Company, sold under the 
trademark "Elvanol" and from Monsanto Co., sold under the trademark 
"Gelvatol". Examples of such products are Elvanol, Grades 71-30, 72-60, 
and 70-05, and Gelvatol, Grades 1-90, 3-91, 1-60, and 3-60. Air Products 
Corp. also sells the product as WS-42. 
The amounts of poly(vinyl alcohol) and wax-asphalt emulsion used should be 
at least about 0.05 wt. percent and about 2 wt. percent respectively. The 
preferred amounts of poly(vinyl alcohol) and wax-asphalt emulsion are 
about 0.15 to about 0.4 wt. percent and about 3.0 to about 5.0 wt. percent 
respectively. Unless stated otherwise, the term "wt. %" when used herein 
and in the claims means weight percent based on the total weight of the 
ingredients of the composition from which the set gypsum core is made, 
said ingredients including the water of the wax-asphalt emulsion, but not 
including additional amounts of water that are added to the gypsum 
composition for forming an aqueous slurry thereof. 
In applications of the type where fire-resistant properties are considered 
important, the core of the fibrous mat-faced gypsum board includes 
preferably one or more additives which improve the ability of the set 
gypsum composition to maintain its integrity when subjected to the heat of 
fire. Examples of materials which have been reported as being effective 
for improving the fire-resistant properties of gypsum products include 
mineral fibers such as, for example, glass fibers, asbestos fibers, and 
calcium sulfate whisker fibers. A mixture of one or more of such fibers 
can be used. Other exemplary materials which are known for use in 
conventional fire resistant gypsum board are unexpanded vermiculite, clay, 
colloidal silica and colloidal alumina. Typically, mineral fibers, and 
particularly glass fibers, are used in admixture with one or more of the 
aforementioned exemplary materials. For example, see U.S. Pat. No. 
3,616,173, assigned to the same assignee as the present invention. 
A preferred material for use in improving the fire resistant properties of 
the fibrous mat-faced gypsum board comprises chopped glass fibers, for 
example, as described in aforementioned U.S. Pat. No. 3,616,173, the 
disclosure of which, as it relates to glass fibers, is incorporated herein 
by reference. Briefly described, said glass fibers are of the drawn 
textile glass fiber type, produced as continuous individual filaments and 
having a diameter of from about 0.0002 to about 0.001". The individual 
filaments are usually grouped into strands, the filaments having coated 
thereon a relatively weak, bonding type material, such as, for example, 
starch or other water softenable or soluble coating material. The bonding 
material helps to prevent abraiding between the several grouped filaments 
of each strand. Prior to the addition of the loosely bonded textile glass 
fibers to the core composition, the strands are cut into short lengths 
such as, for example, 1/8" to 1". Once added to the aqueous slurry 
composition from which the core is made, the bonding or coating material 
dissolves, and the strands separate into individual fibers which become 
uniformly distributed throughout the slurry as the slurry is mixed. 
The presence of mineral fibers in the core of fibrous mat-faced gypsum 
board results in a product which has unusually high fire-resistant 
characteristics. For example, the presence of a predetermined amount of 
chopped glass fibers in the core of glass mat-faced gypsum board of 
predetermined thickness provides a product which has fire resistant 
characteristics that are significantly better than those of conventional 
paper-faced gypsum board that has a like amount of glass fibers in its 
core and a like thickness. The effects which flow from this development 
are significantly important and can desirably be taken advantage in 
several different ways. For example, the development can be used to 
produce a glass mat-faced gypsum board which has a lower density than that 
of conventional paper-faced, glass fiber-containing gypsum board without 
sacrificing fire resistant properties. Similarly, significantly lower 
amounts of glass fibers can be used in the glass mat-faced board without 
sacrificing fire-resistant properties. 
The amount of glass fibers included in the core should be at least about 
0.03 wt.% and can vary over a wide range, for example, from about 0.03 to 
about 0.3 wt. percent based on the total weight of the dry ingredients 
comprising the core, that is, the total weight of the ingredients before 
they are combined with water to make the aqueous slurry from which the 
core is formed. In preferred form, the amount of glass fibers comprises 
about 0.07 to about 0.2 wt. percent. 
The core of the fibrous mat-faced board for use in fire-resistant 
applications can be fabricated according to available techniques into a 
density of desired value. Preferably, the density of the core should not 
exceed about 55 lbs/cu. ft. It is believed that a density within the range 
of about 45 to about 55 lbs/cu. ft. will be used most widely. 
An attractive feature of the present invention is that the fibrous 
mat-faced gypsum board can be made utilizing existing wallboard 
manufacturing lines, for example, as shown somewhat diagramatically in 
FIG. 1. In conventional fashion, dry ingredients (not shown) from which 
the gypsum core is formed are pre-mixed and then fed to a mixer of the 
type commonly referred to as a pin mixer 2. Water and other liquid 
constituents (not shown) used in making the core are metered into the pin 
mixer 2 where they are combined with the dry ingredients to form an 
aqueous gypsum slurry. Foam is generally added to the slurry in the pin 
mixer to control the density of the resulting core. The slurry 4 is 
dispersed through one or more outlets at the bottom of the mixer 2 onto a 
moving sheet of fibrous mat 6. The sheet of fibrous mat 6 is indefinite in 
length and is fed from a roll (not shown) of the mat. 
As is common practice in the manufacture of conventional paper-faced gypsum 
board, the two opposite edge portions of the fibrous mat 6 are 
progressively flexed upwardly from the mean plane of the mat 6 and then 
turned inwardly at the margins so as to provide coverings for the edges of 
the resulting board 40. In FIG. 1, this progressive flexing and shaping of 
the edges of the mat 6 are shown for only one side edge of the mat and the 
conventional guiding devices which are ordinarily employed for this 
purpose are omitted from the figure for the sake of clarity. FIG. 7 shows 
an edge of the set gypsum core 42 covered by the overlapped edge portion 
6A of the mat 6. FIG. 7 shows also score marks 10 and 10A of the mat 6, 
the score marks permitting the formation of good edges and flat surfaces. 
The score marks 10 and 10A are made by a conventional scoring wheel 12. An 
advantage of using the preferred form of glass fiber mat is that it is 
capable of being scored and edged like conventional paper facing. 
Another sheet of fibrous mat 16 is fed from a roll (not shown) onto the top 
of slurry 4, thereby sandwiching the slurry between the two moving fibrous 
mats which form the slurry. The mats 6 and 16 with the slurry 4 sandwiched 
therebetween enter the nip between the upper and lower forming or shaping 
rolls 18 and 20, and are thereafter received on a conveyer belt 22. 
Conventional edge guiding devices, such as indicated at 24 shape and 
maintain the edges of the composite until the gypsum has set sufficiently 
to retain its shape. In due course, sequential lengths of the board are 
cut and further processed by exposure to heat which accelerates the drying 
of the board by increasing the rate of evaporation of excess water in the 
gypsum slurry. 
With reference to FIG. 7, it has been observed that the set gypsum of the 
core 42 is effective in forming satisfactory bonds with the mats and 
between the edge portions of the overlying mat 16 and the overlapped edge 
portion 6A of the underlying mat 6, thus making it unnecessary to use a 
bond improver in the slurry or an edge paste to form the aforementioned 
bonds. 
The preferred form of mats 6 and 16, as shown in FIGS. 2 and 3, comprises 
glass fiber filaments 30 oriented in random pattern and bound together 
with a resin binder (not shown). 
A preferred form of glass fiber mat-faced gypsum board 40 is shown in FIGS. 
4 and 7. It comprises one in which the set gypsum of the core 42 
penetrates substantially through the thickness of the mat 6 over 
substantial area portions thereof and in which the set gypsum of the core 
42 penetrates the mat 16 partially, with the surface being thus 
substantially free of set gypsum. The gypsum-free surface of mat 16, as 
seen in FIG. 8, is highly textured, and provides an excellent substrate 
for adhering thereto an overlying component inasmuch as it comprises many 
interstices into which an adhesive composition can flow and bond. 
The phrase "substantially penetrated by set gypsum", as used herein, means 
that the set gypsum of the core, extends from the mat surface which is 
contiguous to the core to the outer mat surface and coats glass fibers on 
the outer surface with a thin film of set gypsum to the extent that the 
outline of glass fibers can be seen through the thin film of set gypsum. 
The phrase "over substantial area portions of the outer surface", as used 
herein, means that about 30 to 75% of the outer surface area of the mat is 
substantially penetrated by set gypsum. Preferably, about 45 to about 55% 
of the outer surface area of the mat is substantially penetrated by set 
gypsum. Accordingly, the gypsum-coated surface of this preferred 
embodiment of the board comprises a surface that has a roughened or 
patterned appearance; it does not comprise a smooth continuous coating of 
set gypsum. This preferred form of board can be formed with relatively 
small amounts of gypsum slurry being deposited on the underlying support 
surface, thus minimizing the need to clean the surface of the 
board-forming equipment. 
The need for such cleaning can be substantially avoided by adjusting the 
viscosity of the slurry so that it penetrates but part-way through the 
underlying fibrous mat, for example, up to about 50% of its thickness. 
Thus, this preferred form of board has two gypsum-free fiber-faced 
surfaces. 
The manufacture of the aformentioned preferred forms of board can be 
accomplished by controlling the viscosity of the aqueous slurry of the 
calcined gypsum in a manner such that the slurry penetrates the underlying 
and overlying mats to the desired degree. In manufacturing each of the 
aforementioned preferred forms of board, the viscosity of the slurry 
should be such that it penetrates about 10 to 50% of the thickness of the 
overlying mat over the entire surface area thereof. 
The recommended means for controlling the viscosity of the slurry is to add 
thereto a viscosity-control agent. Such viscosity-control agents are known 
in the field of gypsum board manufacture. A preferred viscosity-control 
agent is paper fiber. Examples of other agents that can be used are 
cellulosic thickeners, bentonite clays, starches, and gypsum whisker 
fibers. 
The particular viscosity values that are used in the manufacturing 
operation can vary from one application to the next, depending on the 
porosity of the mat, and the desired penetration of the slurry. 
Accordingly, for any particular application, the viscosity value is best 
determined empirically. 
In using the preferred form of glass fiber mat, as described above, to 
manufacture the aforementioned preferred forms of board, developmental 
work has shown that satisfactory results can be achieved utilizing a 
gypsum slurry having a viscosity within the range of about 5000 to 7000 
cp. As used herein, the viscosity value refers to Brookfield viscosity 
measured at a temperature of 70.degree. F. at 10 rpm utilizing paddle No. 
3. It should be appreciated that the amount of viscosity-control agent 
added to the slurry to give the desired viscosity will vary depending on 
the particular agent used and the specific viscosity desired. 
In preferred form, the core of fibrous mat-faced gypsum board that does not 
include fire-resistant additive(s) has a density of about 40 to about 50 
lbs/cu. ft., most, preferably about 41 to about 45 lbs/cu. ft. The 
manufacture of cores of predetermined densities can be effected by using 
known techniques, for example, by introducing an appropriate amount of 
foam into the aqueous gypsum slurry from which the core is formed. There 
are weight advantages that can be realized by the use of fibrous mat-faced 
gypsum board in that fibrous mats which are lighter in weight than 
conventional paper facing are available. For example, the weight of a 
widely used paper facing in the manufacture of conventional gypsum 
sheathing is in the range of about 120 lbs/1000 sq. ft. of board, whereas 
the weight of a preferred form of glass fiber mat for use in the present 
invention is about 40 lbs/1000 sq. ft. of board. 
Turning now to a description of the finishing material, for use in exterior 
systems, the material should have good weathering characteristics, that 
is, it should resist being degraded by outdoor elements, for example, 
precipitation, rays of the sun and wind. Examples of such finishing 
material include synthetic resinous materials, rubber membranes, asphalt, 
and alternating layers of asphalt and roofing felt. Crushed stone or 
gravel is usually added as a topping to asphalt coatings. 
When the exterior finishing system comprises a poured-in-place roof deck, 
application of the exterior finishing material such as asphalt and roofing 
felt is preceded by application of a settable cementitious material over 
the fibrous mat-faced gypsum board. An example of such settable 
cementitious material is a calcium sulfate, fibered concrete sold by 
Georgia-Pacific Corporation as "Metro Mix". This material comprises a dry 
mixture of calcium sulfate hemihydrate in a dry weight amount of 97 wt. % 
and wood chips in a dry weight amount of about 3%. Water is mixed with the 
dry ingredients of the Metro Mix product to form an aqueous slurry having 
an average testing consistency of 56. 
Insulating material is advantageously used in exterior systems in 
underlying relationship to the finishing material. Presently, the most 
popularly used insulating material in exterior systems, including roof 
deck systems, is expanded or foamed polystyrene, a material which has good 
moisture resistant properties. Although it has desirably low water vapor 
transmission, it is not a vapor barrier, but instead is capable of 
breathing. Rigid panels of expanded polystyrene are used most widely in 
roof deck systems. Such panels have satisfactory compressive strength and 
resilience and are presently available in thicknesses ranging from 1/2 to 
6 inches, widths from 6 to 48 inches and lengths ranging from 4 feet to 16 
feet. One commercially available system utilizes rigid, expanded 
polystyrene panels which are 4'.times.8'.times.1". 
Other thermal insulating materials can be used also. Examples of such 
materials include extruded polystyrene, polyurethane, isocyanurate, 
cement-based insulating plasters, and phenolic foam. Insulating materials 
generally have low thermal conductivity and low density. 
In exterior systems, the fibrous mat-faced, water-resistant gypsum board 
can be affixed to an underlying support member in any suitable way, for 
example, by the use of nails or screws. In such systems, the underlying 
support member may comprise, for example, panels of rigid plastic or metal 
sheets, for example, in corrugated form, purlins and sub-purlins. Panels 
of insulating material may be affixed to such support members and underlie 
panels of said gypsum board which are affixed thereto. The support member 
is typically affixed to the frame of the building. 
The fibrous mat-faced, water-resistant gypsum board can be used also to 
good advantage in other types of exterior applications, including those in 
which it replaces conventional gypsum sheathing. Thus, the board can be 
used as an underlying support surface which is covered with overlying 
finishing materials, for example, aluminum, wood siding, plaster, Portland 
cement stucco, and brick. As described in the aforementioned '874 
application, it can be used also in EISystems. 
The finishing material for use in interior systems should have durability 
characteristics and be preferably appealing in appearance. The most widely 
used interior finishing material is plaster. Especially suitable for use 
in the present invention are the so-called thin coat or veneer plasters. 
An example of one such plaster is sold by Georgia-Pacific Corporation 
under the trademark "Dens-Cote". An example of a plaster made from such a 
product is described in the table below. 
______________________________________ 
Ingredients Wt. % of Dry Ingredients 
______________________________________ 
calcined calcium 
46.15 
sulfate 
sand 24.9 
refined kettle calcined 
22.5 
calcium sulfate 
lime 6.24 
sodium citrate 0.18 
hydroxy propyl methyl 
0.05 
cellulose 
water 38 parts water to 
100 parts dry mix 
______________________________________ 
Numerous other interior finishing plasters are known for interior surfacing 
of walls, ceilings, and the like. A number of these are described in the 
Georgia-Pacific brochure entitled "Plaster Products Denscote Veneer Lath 
and Plaster", mentioned hereinabove. 
The interior finishing material can vary in thickness, as desired, minimum 
exemplary thicknesses being about 1/16" to about 1/4". Preferably, the 
plaster finish comprises a mono-layer of plaster; however, multi-layers of 
plaster can be used also, applied in thicknesses in excess of 1/4". In 
interior systems, the fibrous mat-faced, water-resistant gypsum board can 
be affixed to an underlying support member in any suitable way, for 
example, by the use of mechanical fasteners such as nails and screws. The 
underlying support member can comprise a wooden or metal frame which 
includes studs. In some applications, the panels of the board may be 
affixed directly to the interior surface of an inside wall, for example, 
one comprising cinder blocks or concrete blocks. In new construction, the 
board is typically affixed directly to the frame of the building. 
A typical roof deck system incorporating the fibrous mat-faced gypsum board 
as described above is shown in FIGS. 10 to 12. In this construction, 
spaced parallel trusses 50 extending between building support members (not 
shown) support a corrugated metal deck 52 which is welded or otherwise 
fastened to the trusses. Layers 54 and 56 of insulating sheet material, 
which may, for example, be of expanded polystyrene, are disposed on the 
corrugated metal deck. A layer 58 of fibrous mat-faced gypsum board panels 
of the type described hereabove are secured to the corrugated deck 52 by 
means of fasteners 60 passing therethrough and through the underlying 
insulation layers 54 and 56 into the deck 52. The joints of the panel 
layer 58 are sealed by application of tape 62, as shown in FIG. 10 with 
respect to one of the panel joints. Overlying the gypsum layer 58 is a 
waterproof roofing membrane comprising alternate layers of asphalt 64 and 
roofing felt 66, three layers of each being shown in the present example. 
A final coating of asphalt 68 is covered with a crushed gravel topping 
layer 70. 
In the enlarged view of FIG. 12, the manner in which the first asphalt 
layer 64 penetrates into the upwardly facing fibrous mat-face of the 
gypsum board panel layer 58 is illustrated. This penetration assures a 
secure adhesion of the waterproof membrane to the structural layers of the 
roof system. 
Referring to FIGS. 13 and 14, a poured-in-place roof deck system is shown 
comprising purlins 72 supporting spaced sub-purlins (bulb tees 74 in 
parallel spaced relation). Fibrous mat-faced gypsum board panels 76 of the 
type described above are supported on the horizontal flanges 74a of the 
sub-purlins 74. A reinforcing mesh screen 78 is laid over the sub-purlins 
and gypsum board panels 76 and a layer of settable cementitious slurry 80 
is poured in place over the reinforcing mesh. The slurry 80 is allowed to 
harden to form a smooth continuous deck surface 82. Adhesion of the slurry 
to the gypsum board panel 76 is assured by the penetration of the slurry 
into the upwardly facing fibrous mat surface of the panels. A roofing 
membrane comprising alternate layers of asphalt 4 and roofing felt 86, 
three layers of each in the illustrated example, is applied to the surface 
82. A final layer of asphalt 88 is covered with a coating of crushed rock 
or gravel 90. 
An example of an interior usage of the present fibrous mat-faced panel is 
illustrated in FIGS. 15 and 16. In these views, an interior wall system 
comprises spaced vertical studs 92 to which fibrous mat-faced gypsum board 
panels 94 in accordance with the invention are attached by spaced 
fasteners 96 such as screws or nails. A thin layer 98 of plaster is 
applied to the fibrous mat surface 100 of the panel 94 and is troweled to 
form a smooth finish surface which may then be decorated by paint, paper 
or the like in a conventional manner. As shown in the enlarged view of 
FIG. 16, the plaster 98 penetrates into the fibrous mat surface of the 
panel 94 to effect a secure mechanical bond of the plaster layer to the 
panel. Although shown in the context of a wall in FIG. 15, the panel 94 
may equally suitably be used as a ceiling panel and can be used with 
either a wood or metal stud support system. For some applications, it may 
be found that adjustments need to be made in the water-resistant 
properties of the core in order to obtain a satisfactory plaster finish. 
For example, it may be found expedient to adjust the amount of the 
water-resistant additive(s) in the core in a manner such that the water 
absorbancy of the core (as determined according to the aforementioned ASTM 
C-473) is 10% or greater, for example, up to about 20%. 
EXAMPLES 
EXAMPLE NO. 1 
The formulation set forth below is an example of a preferred aqueous gypsum 
slurry which can be used in making the core of a gypsum support member for 
use in an exterior or interior finishing system. 
______________________________________ 
Lbs./1000 
Constituents sq. ft. of board 
______________________________________ 
calcined gypsum 1380 
(CaSO.1/2H.sub.2 O) 
wax/asphalt emulsion 130 
aqueous solution of 10 wt % 
56 
poly (vinyl alcohol) 
paper fiber 15 
set accelerator 6 
ammonium lauryl sulfonate (foaming agent) 
1 
calcium lignosulfonate (dispersing agent) 
2 
water 
______________________________________ 
The wax/asphalt emulsion used in the above formulation contained 
approximately 48 wt. % solids of which about 11 wt. % was paraffin wax and 
about 37 wt. % was asphalt. The set accelerator comprised about 80 wt. % 
potash, about 12 wt. % lignosulfonate and about 8 wt. % ground gypsum. 
The above formulation was used to prepare gypsum board, the surfaces of 
which were covered with nonwoven fiber glass mat. The mat was composed of 
glass fiber filaments oriented in a random pattern bonded together by an 
adhesive referred to by the manufacturer as a "modified urea-formaldehyde 
resin". The mat had a thickness of 33 mils and was more porous than paper 
of the type used as the cover sheet of gypsum wallboard. The air 
permeability of the mat was 700 CFM/sq. ft. (test method FG 436-910). The 
mat is available commerically as DURA-GLASS 7502-2 lbs. and is an example 
of a preferred fibrous mat for use in the practice of the present 
invention. 
Continuous length board was made from the above gypsum slurry and glass 
fiber mat on a conventional wallboard machine. The slurry was fed onto a 
moving sheet of the mat as it was unrolled from a roll onto a moving 
support surface. The mat had a width of about 51 inches and was scored 
continuously by conventional scoring blades prior to the deposition of the 
slurry thereon. Each edge of the mat was scored with two score marks, with 
each of the outer scores being about 1 inch from its respective edge of 
the mat and each of the inner scores being about 11/2 inch from its 
respective edge. After the slurry was deposited on the mat, the edges were 
folded at the score marks and overlapped on top of the slurry. (The gypsum 
core formed from this operation had a width of 477/8 inches and a 
thickness of 1/2 inch.) Mat from another roll thereof and having a width 
of 471/2 inches was fed onto the top of the gypsum slurry and the 
overlapped edge portions of the underlying mat. The gypsum slurry 
penetrated the overlapped edge portions and served to bond the edge 
portions of the overlying mat to the overlapped edge portions of the 
underlying mat. 
The viscosity of the gypsum slurry was about 5900 cp at 70.degree. F. At 
this viscosity, the slurry penetrated substantially through some portions 
of the underlying mat to form a thin film thereof on about 40 to 50% of 
the area of the outer surface of the mat. As the gypsum in the film set, 
substantial portions of the outer surface of the mat were covered with a 
thin film of set gypsum. The surface had a roughened appearance with 
outlines of the glass filaments being observable underneath the thin 
coatings of gypsum which covered them. However, at the aforementioned 
viscosity, the slurry penetrated but a portion (about 5 mils) of the 
thickness of the overlying mat over the entire area thereof, with no 
slurry being observed on the outer surface of the mat. As the gypsum set 
in the intermediate portions of the mat that were penetrated by the 
slurry, it formed a bond that included a mechanical interlock with the set 
gypsum core. 
The continuous length board is cut into lengths of about 8, 10 or 12 feet. 
Drying of the gypsum board is accelerated by heating in an oven at 
350.degree. F. for about 2 hours and until the board is almost dry and 
then at 200.degree. F. for about 1 hour until it is dried completely. The 
density of the board is about 43 lb./cu.ft. 
Glass fiber-faced gypsum boards, made as described above, and with their 
edges protected, were placed outdoors for several months and exposed to 
the elements. During that period, the boards were examined and found to be 
in excellent condition with no signs of deterioration. Other outdoor tests 
have shown that glass fiber mat-faced gypsum board having a core which 
includes wax-asphalt emulsion as a water-resistant additive better resists 
deterioration than a like board having a core which includes sodium methyl 
soliconate as the water-resistant additive. 
Board of Example 1 above can be used advantageously pursuant to the present 
invention in exterior and interior finishing systems particularly of the 
type in which it is not deemed important for the board to have relatively 
high fire-resistant properties. For use in systems where it is considered 
important for the board to have relatively high fire-resistant properties, 
(as well as good water-resistant properties), the board of Example No. 2 
below is exemplary. The Board of Example No. 2 is a 5/8 " thick glass 
fiber mat-faced gypsum board having a core composition as set forth below 
and prepared according to the technique described for glass fiber 
mat-faced gypsum board of Example No. 1 above. 
______________________________________ 
Components Wt. %, set & dried board 
______________________________________ 
glass fiber mat facing 
1.58 
calcium sulfate dihydrate 
94.06 
glass fiber (1/2" chopped 
0.08 
glass roving) 
paper fiber 0.74 
potash (accelerator) 
0.15 
wax-asphalt 2.96 
poly (vinyl alcohol) 
0.28 
calcium lignosulfonate (dispersing 
0.11 
agent) 
ammonium lauryl sulfonate 
0.04 
(foaming agent) 
______________________________________ 
The density of the core of the board was 53 lbs/cu. ft. A fire rating of 1 
hour and 30 seconds was achieved when the board was evaluated for fire 
resistance and hose stream resistance according to ASTM E-119. It is noted 
that the board has excellent water-resistant properties due to the use of 
water-resistant additives in its core, those additives being wax-asphalt 
emulsion and poly(vinyl alcohol). 
It should be understood that gypsum board as described herein can be used 
in applications other than the specific ones described hereinabove. For 
example, such gypsum board can be used to excellent advantage in mobile 
homes, that is, prefabricated or manufactured housing of the type wherein 
buildings, usually dwellings, are manufactured in a factory, including, 
for example, in sections which are transported to site and assembled to 
form a finished building. In such systems, it is particularly desirable 
that gypsum board used in forming the walls and ceilings of the mobile 
home be light in weight to reduce transportation costs and be resistant to 
sagging, as tends to occur when veneer plasters and textured interior 
finishes are applied thereto. Such overlying finishes are typically 
applied by spraying. 
When evaluated for sag or humidified deflection according to ASTM C-473, 
one type of commercially available, paper-faced 1/2" thick gypsum board 
shows a humidified deflection of 10/8". A similar 3/8" board shows a 
humidified deflection of 15/8". It is noted that conventional gypsum 
board, the core of which includes water-resistant additives fares even 
worse in humidified deflection tests than the aforementioned commercially 
available gypsum boards. 
On the other hand, when a 1/2" thick glass mat-faced board having a core 
composition according to Example 1 herein is tested according to ASTM 
C-473, the board shows a humidified deflection measurement of less than 
1/8". Such board or one having a thickness of 5/16", a preferred thickness 
for use in mobile homes, can be used effectively in mobile home 
applications. 
It is noted that the compositions of the examples included the use of 
calcium sulfate hemihydrate to form the set gypsum product. Alternatively, 
there can be used calcium sulfate, the term used in the claims to cover 
generically both soluble anhydrous calcium sulfate and calcium sulfate 
hemihydrate. 
In summary, it can be said that the present invention provides improvements 
in exterior and interior finishing systems, including systems which are in 
relatively wide use in industry. The improvements are provided in a 
practical way which promotes their being adopted readily, thereby helping 
to assure that the benefits of the invention are realized by the 
installers and users of the systems.