Also known as Sheetrock, Gyprock, etc. I will discuss drywalling a room; this is intended as a simplified guide for the homeowner, not a guide for the professional. See the separate topic on drywall patching.
Drywall Types
Three common types: standard, water resistant
(green board), and fire code Type X. Standard comes most commonly in 1/2" and 1/4" thickness.
Greenboard comes in 1/2" and 5/8". Fire code type is most commonly
in 5/8" thickness and it is labeled. I read that there is now a non-sag 1/2" drywall for
use on ceilings, but have not seen it.
Sheet Size
Most common is 4x8'. It is available in
lengths beyond that in 2' increments, 4x12' being the most common. You may also be
able to get it in 54" widths at a drywall supplier. Weight of standard 1/2" 4x8
is about 54 pounds.
Support
Drywall has to be supported by framing. The 1/2"
thickness needs framing on 16" centers or less. Codes are being tightened
for support of ceiling panels and some codes now call for 5/8" drywall on ceilings
to prevent sagging. Make the joints on framing, but the sheets will by nature have
to bridge across the stud space or joist space.
Drywall can be glued to other dry surfaces,
such as concrete block or plaster, providing the surface is flat enough. Construction
adhesive rated for the two materials would be my choice. Use the kind that is
trowelled on to give complete coverage, or trowel out the stuff from a caulking tube.
You will have to use a few fasteners to hold the drywall in place while the adhesive
cures or else brace it until the adhesive cures. If the surface is not flat, it
would be best to fasten nailing strips (sleepers) of wood to the surface and fasten
the drywall to them.
Where Used
Standard 1/2" drywall and greenboard can be used in
most rooms of the house; they are not suitable for wet locations such as
showers or unprotected tub surrounds. Neither of these is acceptable for
ceramic tile backing. Greenboard would be suitable for a bathroom except
for tile backer, but regular drywall can also be used. I hear that greenboard
has anti-mildew properties but have not confirmed this: if true, then it would be
the material of choice for bathrooms.
Type X 5/8" drywall is used most commonly in a garage
as a fire protection surface for a wall or ceiling backing up to the inside
of the house. In some codes, it must be double thickness for this use.
The 1/4" thickness is not needed often but is useful
for making curved walls, or to build up thickness to match another surface,
or as overlay to cover a bad surface such as damaged plaster. Because of its weight
and lack of strength, it is hard to handle. It is best to apply it with
adhesive and temporary fasteners. Construction adhesive in a caulking
tube will work but trowelled on adhesive will work better. For a curved wall,
you can dampen the convex curved surface to make it more flexible. You can get
it pretty wet, without harm, if it can dry off rapidly.
Horizontal or Vertical?
Pros usually set drywall sheets horizontally because
it requires less taping, but this is only true if you use
larger than 4x8 sheets. For example, a wall 8' high and 12' long can be covered
with two 4x12 sheets set horizontally. The factory recessed edge will be horizontal
at mid wall where it is less obvious. For the inexperienced, there is no reason why wall
sheets cannot be set vertically. Thus that 8x12' wall would take three 4x8 sheets,
which are a lot easier to handle. Setting the sheets horizontally means less taping
but unless you are working to a production goal, that just isn't important. Setting
sheets vertically will mean that the factory recessed edge is available for all
joints except for some corners where it is cut.
The factory recessed edge can be taped and filled absolutely flat; more on this
later. Ceilings are another matter; here you want to plan the drywall layout for
minimum end joints. Set the sheets lengthwise across the joists.
The factory recessed edge will then float between the joists, and when it is
taped and filled, it will be strong enough.
Lifting Drywall
You drywall ceilings before walls so the wall sheets
help support the ceiling sheets. If you set the wall sheets vertically, you have
no great problem tilting them in place by yourself. Lifting them
into the room will be more of a problem, and a helper will be welcome
there. Lifting a sheet to the ceiling is a challenge! A drywall lift
can do that nicely, and you can rent them. I have never used one but I understand
they can be disassembled so they can be moved down into a basement. Another method you
can use to get the ceiling
sheets in place is to nail a 2x4 across the studs about 2" down from the
ceiling joists and lift the edge of the sheet up on the 2x4. With one or
two edges supported in that manner, it is easier (but still not easy!) to lift the rest
of the sheet in place and start fastening. A helper in the form of a T-brace
will make it easier. Make one with an overall length about 1/2"
more than the net ceiling height; nail a 24" 2x4 to the end to push against
the sheet. Another trick you can use is to set the sheet on top of a 6'
step ladder on its way to the ceiling.
Story: I watched a pro drywall crew do a room in
a home some years ago. The ceiling man had one of these adjustable metal
sawhorses ("strongback") set just so, and he wore a Navy watch cap. He
hefted the sheet up on his head, stepped up on the strongback and pushed
the sheet up to the ceiling. Then he tack nailed it in place with one nail
in the center! Pros sometimes use special stilts strapped to their legs to
do the ceilings but OSHA does not allow these because they are leg breakers.
In doing a room, get the ceiling drywall in place and tip
up the wall sheets. Push the wall sheet up solidly against the ceiling drywall
using a flat prybar or a drywall roller lift at the floor. This will leave a small
gap at the floor, which is acceptable.
Truss Lift
If you are applying drywall to a ceiling that
is directly under truss framing for a roof, be aware of the phenomenon called
Truss Lift. A roof truss is a framework that is assembled in a factory using pressed-on
gang nail plates and the truss assemblies are installed on the walls on the
building site. The bottom chord of the truss becomes the ceiling joist. The truss will
expand/contract differently than you would expect of non-truss framing, and this
seasonal event will cause the bottom chord to rise and fall in the center portion
of the chord. An interior wall - one near the center of the truss - cannot be
fastened solidly to the bottom chord or structural damage will occur. More
importantly to you, the drywall joint between an interior wall and the ceiling
will crack if it is fastened in the usual manner, and this crack can be as much as
1/2". What you need to do is fasten the ceiling drywall normally except for about
2' out from the interior wall. This portion of the drywall will "float". The corner
joint between the ceiling and wall drywall can be taped and filled in the usual
manner and it will flex enough to keep from cracking. This seasonal rise and fall
of the ceiling is usually not obvious if the ceiling drywall floats properly.
Since the truss rests on the exterior walls, nothing special needs to be done
at that point; fasten the drywall as usual.
Cutting Techniques and Tools
Cutting drywall is usually done somewhat crudely,
in the interest of speeding up the job; the crude cuts will be covered by
compound in the end. Make your cuts about 1/8" shy of the space so it will
not bind. An experienced drywaller will mark the drywall for cutting with
the point of a utility knife and then score the face with the knife along
a straightedge. Pressing against the backside of the cut with a knee or
hand will snap the face of the sheet. Then with the sheet folded slightly,
the backside paper can be cut and the sheet is snapped in the other direction
to complete the cut. Once you learn this technique (which is easy to learn)
the cuts can be made very rapidly. The straightedge must be 48" long to go
across the sheet. The best form of straightedge is a T-square made especially
for drywall. If you have no such straightedge, get the T-square tool; it
is not expensive. I prefer the kind with a removable T head since it
can be used for other jobs as well.
Cutting a notch or corner out of a sheet is a little
more difficult, and you may wish to saw one direction and snap the other.
You can cut a round hole in a sheet with a drywall saw. The typical drywall saw
is a pointed keyhole saw that can be used for curved cuts; they are cheap and
expendable since drywall is hard on the teeth. I also use an old toolbox handsaw
for longer straight cuts; when it gets too dull for cutting wood, I mark it and
use it for cutting drywall. To smooth off nubs where the sheet did not snap
smoothly, you can use a drywall plane or saw or a knife. A drywall plane
is typically a piece of expanded metal fastened to a wood block. I have
one but seldom use it; the knife is usually right at hand.
There is a special powered cutter that is very handy
if you are doing a lot of drywalling. This is a RotoZip tool; it is like a
miniature router with a 1/8" collet and many different types of bits for
different purposes. Some of these can even cut through ceramic tile. Use the
drywall bit that has a smooth end to guide the bit around some object and
spiral cutting edges that throw the dust away from the tool and you. One
way of using this to good advantage is to drywall over the top of a door
opening. These corners should not be pieced since they are stress points.
So by fastening the sheet over the opening, you can use the RotoZip to cut
around the opening; this opening can also be cut with a handsaw. In the
same manner, the RotoZip can be used to cut around the outside of electrical
boxes and similar objects.
Marking holes for electrical boxes can
be a problem at times. The neatest trick I have heard for this is to mark the
location of such wall boxes on the floor, with a notation of the height; if
you are working over a floor you do not want to mark, you can put these notes
on masking tape on the floor. Then hang the sheet from the top and cut the
hole with a drywall saw, based upon the measurements.
Fasteners and Tools
Nailing is the most common method, using
either chem etched nails or ring shank nails. These are designed to lock
into the wood framing and stay in place for the life of the structure.
These work whether the wood framing is wet or dry. Nailing is a reliable
method of fastening and probably the best for the inexperienced. Typical
chem etched nail length is 5p, or 1-5/8"; typical ring shank nail length is 1-1/4".
Chem etched nails are very sharp and are easy to drive; ring shank nails
are much harder to drive and I don't recommend them. Nail spacing is typically
every 6" around the edges of the sheet and every 8" on studs and joists in the
field. The nails must be set just below the surface but without breaking the face
paper; this is not difficult to do. If you are working in a situation where
you fear hammering on the wall could damage other work, screws are the way
to go. This is particularly true of remodeling work and patching.
A drywall hammer is light weight, either
all steel or wood handle. The weight is important because hammering
a lot of nails can be tiring on the wrist; the standard chem etched
nails drive easily so a heavy hammer is not required. The back of the hammer
head is a small hatchet for knocking off projections or punching crude
holes. A standard claw hammer can be used for small jobs; you need not
buy a special hammer unless you will be doing a lot of drywall work.
Screwing drywall is a more reliable fastening
method, but to be so, it takes a special power screwdriver. A good
driver can be adjusted to set the screw reliably to the precise depth
required; this is with the head slightly below the surface but without
breaking the face paper. This is not easy to do without a good driver.
The driver has a clutch for the bit that disengages when the screw reaches
the correct depth. There are very simple driver bits for standard powered
screwdrivers but I have not found them reliable. Note that the screws
have a Philips slot and the driver bit cams out of that slot as the screw
reaches the correct depth. A more positive driver shape, like a square
(Robertson) head, cannot be used.
I watched a pro use a Senco driver once.
He would turn it on with a toggle switch and not turn it off until he was through
with that part of the job. He would grab a handful of screws and set one on
the bit. The bit was stationary at that point, but as soon as he pressed the point
of the screw to the drywall, the clutch would engage and set the screw. As it reached
the correct depth, the bit would disengage and stop. Then he would go to the next screw.
This was a very fast process; he would zing, zing, zing across the sheet.
Spacing of screws can be wider because they hold
better, but approach this cautiously. Typically something like every 8" around the
edges and every 12" in the field. Some codes allow wider spacing but I strongly
recommend against using that; in fact, I recommend you space screws the same as nails.
Without enough fasteners, the panels will vibrate
on the studs and may bow, particularly on ceilings. Screw length for 1/2"
drywall is 1-1/4". Use coarse thread screws; they are easier to drive in wood
and they hold better. For steel studs you need the fine thread screws with
a drill point. However, I have found that pointed fine-thread screws work just
as well on thin steel.
Some codes allow double nailing or screwing.
This is a technique where you put two nails close together but use a wider spacing
to the next pair of nails. Overall, you use the same number of fasteners. I
definitely do not favor this method. The sheets can vibrate and come loose easier.
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