View Full Article At - https://en.wikipedia.org/wiki/Drywall Gypsum board hit the
market place between 1910 and 1930 beginning with wrapped board edges, and
elimination of the two inner layers of felt paper in favor of paper-based facings. In
1910 United States Gypsum Corporation bought Sackett Plaster Board Company and
by 1917 came out with a product they called Sheetrock.- Providing efficiency of
installation, it was developed additionally as a measure of fire resistance - Later air
entrainment technology made boards lighter and less brittle, then joint treatment
materials and systems also evolved.

Rock lath (gypsum lath) was an early substrate for plaster. An alternative to
traditional wood or metal lath, it was a panel made up of compressed gypsum
plaster board that was sometimes grooved or punched with holes to allow wet
plaster to key into its surface. As it evolved, it was faced with paper impregnated
with gypsum crystals that bonded with the applied facing layer of plaster

Coal-fired power stations include devices called scrubbers to remove sulphur from
their exhaust emissions. The sulphur is absorbed by powdered limestone in a
process called flue-gas desulphurization (FGD), which produces a number of new
substances. One is called "FGD gypsum". This is commonly used in drywall
construction in the United States and elsewhere.

Drying chambers typically use natural gas today. To dry 1 MSF ( 1,000 square feet
(93 m2) ) of wallboard, between 1,750,000 and 2,490,000 BTU (1,850,000 and
2,630,000 kJ) is required. Organic dispersants/plasticisers are used so the slurry will
flow during manufacture, and to reduce the water and hence the drying time.

Most plasterboard is made in 120 cm-wide sheets, though 90 cm and 60 cm wide
sheets are also made. 120 cm wide plasterboard is most commonly made in 240 cm
lengths, though 250, 260, 270, 280, 300 cm and even longer (if ordered) are
commonly available.

Plasterboard is commonly made with one of three different edge treatments:
tapered edge, where the long edges of the board are tapered with a wide bevel at
the front to allow for jointing materials to be finished flush with the main board
face; plain edge, used where the whole surface will receive a thin coating (skim
coat) of finishing plaster; and, finally, bevelled on all four sides, used in products
specialised for roofing. However four side chamfered drywall is not currently
offered by major UK manufacturers for general use.

Drywall is delivered to a building site on a flatbed truck and unloaded with a forked
material handler crane. The bulk drywall sheets are unloaded directly to upper
floors via a window or exterior doorway.

As an alternative to a week-long plaster application, an entire house can be
drywalled in one or two days by two experienced drywallers, and drywall is easy
enough to use that it can be installed by many amateur home carpenters. In large-
scale commercial construction, the work of installing and finishing drywall is often
split between the drywall mechanics, or hangers, who install the wallboard, and the
tapers and mudmen, or float crew, who finish the joints and cover the fastener
heads with drywall compound.[citation needed] Dry wall can be finished anywhere
from a level 0 to a level 5, where 0 is not finished in any fashion and 5 is the most
"pristine". Depending on how significant the finish is to the customer the extra steps
in the finish may or may not be necessary, though priming and painting of drywall is
recommended in any location where it may be exposed to any wear.

Drywall screws are designed to be self-tapping.

Drywall is cut to size, using a large T-square, by scoring the paper on the finished
side (usually white) with a utility knife, breaking the sheet along the cut, and cutting
the paper backing. Small features such as holes for outlets and light switches are
usually cut using a keyhole saw or a small high-speed bit in a rotary tool. Drywall is
then fixed to the wall structure with nails or drywall screws and often glue.

Drywall fasteners, also referred to as drywall clips or stops, are gaining popularity in
both residential and commercial construction. Drywall fasteners are used for
supporting interior drywall corners and replacing the non-structural wood or metal
blocking that traditionally was used to install drywall. Their function serves to save
on material and labour expenses, to minimize call-backs due to truss uplift, to
increase energy efficiency, and to make plumbing and electrical installation simpler.

Drywall screws heads have a curved taper, which allows them to self-pilot and
install rapidly without having to be punched through the paper cover. When finished
driving, these screws are recessed slightly into the drywall. Screws for light-gauge
steel framing have an acute point and finely spaced threads. If the steel framing is
heavier than 20-gauge, self-tapping screws with finely spaced threads must be used.
In some applications, the drywall may be attached to the wall with adhesives.

Men apply joint compound to drywall.

After the sheets are secured to the wall studs or ceiling joists, the installer conceals
the seams between drywall sheets with joint tape and several layers of joint
compound (sometimes called mud). This compound is also applied to any screw
holes or defects. The compound is allowed to air dry then typically sanded smooth
before painting. Alternatively, for a better finish, the entire wall may be given a skim
coat, a thin layer (about 1 mm or 1/16 inch) of finishing compound, to minimize the
visual differences between the paper and mudded areas after painting.

Another similar skim coating is always done in a process called veneer plastering, although it
is done slightly thicker (about 2 mm or 1/8 inch). Veneering uses a slightly different
specialized setting compound ("finish plaster") that contains gypsum and lime putty. This
application uses blueboard, which has special treated paper to accelerate the setting of the
gypsum plaster component. This setting has far less shrinkage than the air-dry compounds
normally used in drywall, so it only requires one coat. Blueboard also has square edges rather
than the tapered-edge drywall boards. The tapered drywall boards are used to countersink the
tape in taped jointing whereas the tape in veneer plastering is buried beneath a level surface.
One coat veneer plaster over dry board is an intermediate style step between full multi-coat
"wet" plaster and the limited joint-treatment-only given "dry" wall.

Sound control

The method of installation and type of drywall can reduce sound transmission
through walls and ceilings. Several builders' books state that thicker drywall reduces
sound transmission, but engineering manuals recommend using multiple layers of
drywall, sometimes of different thicknesses and glued together, or special types of
drywall designed to reduce noise.[15] Also important are the construction details of
the framing with steel studs, wider stud spacing, double studding, insulation, and
other details reducing sound transmission. Sound transmission class (STC) ratings
can be increased from 33 for an ordinary stud-wall to as high as 59 with double 1/2"
drywall on both sides of a wood stud wall with resilient channels on one side and
fiberglass batt insulation between the studs.

Water damage and mold

Drywall water damage in a closet.

Drywall is highly vulnerable to moisture due to the inherent properties of the
materials that comprise it: gypsum, paper, and organic additives and binders.
Gypsum will soften with exposure to moisture, and eventually turn to a gooey paste
with prolonged immersion, such as during a flood. During such incidents, some or all
of the drywall in an entire building may need to be removed and replaced.
Furthermore, the paper facings and organic additives mixed with the gypsum core
are food for mold. The porosity of the board—introduced during manufacturing to
reduce the weight of the board, lowering construction time and transportation
costs—enables water to rapidly reach the core through capillary action, where mold
can grow inside. This capillary action can result in water spilled at the base of a wall
being wicked upwards and damaging the material up to several inches off the
ground. Finally, drywall's paper facings are edible to termites, which can eat the
paper if they are infesting a wall cavity that is covered with drywall. This causes the
painted surface to crumble to the touch, its paper backing material having been
eaten. In addition to the necessity of patching the damaged surface and repainting,
if enough of the paper has been eaten, the gypsum core can easily crack or crumble
without it and the drywall must be removed and replaced.


Drywall damage caused by termites eating the paper, causing the paint to crumble.
Water that enters a room from overhead may cause ceiling drywall tape to
separate from the ceiling as a result of the grooves immediately behind the tape
where the drywall pieces meet become saturated. The drywall may also soften
around the screws holding the drywall in place and with the aid of gravity, the
weight of the water may cause the drywall to sag and eventually collapse, requiring
replacement.

In many circumstances, especially when the drywall has been exposed to water or
moisture for less than 48 hours, professional restoration experts familiar with
structural drying methodologies can introduce rapid drying techniques designed to
eliminate necessary elements required to support microbial activity while also
restoring most or all of the drywall and thus avoiding the cost, inconvenience, and
difficulty of removing and replacing the affected drywall.

It is for these reasons that greenboard and ideally cement board are used for rooms
expected to have high humidity, primarily kitchens, bathrooms, and laundry rooms.

Fire resistance

When used as a component in fire barriers, drywall is a passive fire protection item.
In its natural state, gypsum contains the water of crystallization bound in the form
of hydrates. When exposed to heat or fire, this water is vaporised, over a range of
temperatures from 80° to 170 °C (see calcium sulphate), retarding heat transfer until
the water in the gypsum is gone. This makes drywall an ablative material because as
the hydrates sublime, a crumbly dust is left behind, which, along with the paper, is
sacrificial. Generally, the more layers of Type X drywall one adds, the more one
increases the fire-resistance of the assembly, up to four hours for walls and three
hours for ceilings.[19] Evidence of this can be found both in publicly available design
catalogues, including DIN4102 Part 4 and the Canadian Building Code on the topic,
as well as common certification listings, including certification listings provided by
Underwriters Laboratories and Underwriters Laboratories of Canada (ULC). "Type
X" drywall is formulated by adding glass fibres to the gypsum, to increase the
resistance to fires, especially once the hydrates are spent, which leaves the gypsum
in powder form. Type X is typically the material chosen to construct walls and
ceilings that are required to have a fire-resistance rating.

Fire testing of drywall assemblies for the purpose of expanding national catalogues,
such as the National Building Code of Canada, Germany's Part 4 of DIN4102 and its
British cousin BS476, are a matter of routine research and development work in
more than one nation and can be sponsored jointly by national authorities and
representatives of the drywall industry. For example, the National Research Council
of Canada routinely publishes such findings.[20] The results are printed as approved
designs in the back of the building code. Generally, exposure of drywall on a panel
furnace removes the water and calcines the exposed drywall and also heats the
studs and fasteners holding the drywall. This typically results in deflection of the
assembly towards the fire, as that is the location where the sublimation occurs,
which weakens the assembly, due to the fire influence.

Cosponsored tests result in code recognized designs with assigned fire-resistance
ratings. The resulting designs become part of the code and are not limited to use by
any one manufacturer. However, individual manufacturers may also have
proprietary designs that they have had third-party tested and approved. This is
provided that the material used in the field configuration can be demonstrated to
meet the minimum requirements of Type X drywall (such as an entry in the
appropriate category of the UL Building Materials Directory or in the Gypsum
Association Fire Resistance and Sound Control Design Manual) and that sufficient
layers and thicknesses are used. Fire test reports for such unique third party tests
are confidential but may be made available to code officials upon special request.

It's important to consider deflection of drywall assemblies to maintain their
assembly integrity to preserve their ratings. Deflection of drywall assemblies can
vary somewhat from one test to another. Importantly, penetrants do not follow the
deflection movement of the drywall assemblies they penetrate. For example, see
cable tray movement in a German test. It is, therefore, important to test firestops in
full scale wall panel tests, so that the deflection of each applicable assembly can be
taken into account.

The size of the test wall assembly alone is not the only consideration for firestop
tests. If the penetrants are mounted to and hung off the drywall assembly itself
during the test, this does not constitute a realistic deflection exposure insofar as the
firestop is concerned. In reality, on a construction site, penetrants are hung off the
ceiling above. Penetrants may increase in length, push and pull as a result of
operational temperature changes (e.g., hot and cold water in a pipe), particularly in
a fire. But it is a physical impossibility to have the penetrants follow the movement
of drywall assemblies that they penetrate, since they are not mounted to the
drywalls in a building.

It is, therefore, counterproductive to suspend penetrants from the drywall assembly
during a fire test. As downward deflection of the drywall assembly and buckling
towards the fire occurs, the top of the firestop is squeezed and the bottom of the
firestop is pulled. This is motion above that caused by expansion of metallic
penetrants due to heat exposure in a fire. Both types of motion occur because
metal first expands in a fire, and then softens once the critical temperature has
been reached, as is explained under structural steel. To simulate the drywall
deflection effect, one can simply mount the penetrants to the steel frame holding
the test assembly. The operational and fire-induced motion of the penetrants,
which is independent of the assemblies penetrated, can be separately arranged.


Types Of Drywall Available In The USA

Regular white board, from 1/4" to 3/4" thickness
Fire-resistant ("Type X"), different thickness and multiple layers of wallboard provide
increased fire rating based on the time a specific wall assembly can withstand a
standardized fire test. Often perlite, vermiculite, and boric acid are added to
improve fire resistance.

Greenboard, the drywall that contains an oil-based additive in the green coloured
paper covering that provides moisture resistance. It is commonly used in wash
rooms and other areas expected to experience elevated levels of humidity.[26]
Blueboard, blue face paper forms a strong bond with a skim coat or a built-up
plaster finish providing both water and mould resistance. Cement board, which is
more water-resistant than greenboard, for use in showers or sauna rooms, and as a
base for ceramic tile.

Soundboard is made from wood fibres to increase the sound transmission class.
Soundproof drywall is a laminated drywall made with gypsum and other materials
such as damping polymers to significantly increase the sound transmission class
rating.

Mould-resistant, paperless drywall.
Enviroboard, a board made from recycled agricultural materials
Lead-lined drywall, a drywall used around radiological equipment.[28]
Foil-backed drywall used as a vapour barrier.

Controlled density (CD), also called ceiling board, which is available only in 1/2"
thickness and is significantly stiffer than regular white board.

EcoRock, a drywall that uses a combination of 20 materials including recycled fly
ash, slag, kiln dust and fillers and no starch cellulose; it is advertised as being
environmentally friendly due to the use of recycled materials and an energy
efficient process.

Gypsum “Firecode C”. This board is similar in composition to Type X, except
for more glass fibres and a form of vermiculite, used to reduce shrinkage.
When exposed to high heat, the gypsum core shrinks but this additive
expands at about the - same rate, so the gypsum core is more stable in a
fire, and remains in place even after the gypsum dries up.
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