Plastering

Modern interior plastering techniques
There are two main methods in USA used in construction of the interior walls of modern homes, plasterboard, also called drywall, and veneer plastering.
Main article: Plasterboard
In plasterboard a specialized form of sheet rock known as "greenboard" (because on the outer paper coating is greenish) is screwed onto the wall-frames (studs) of the home to form the interior walls. At the place where the two edges of wallboards meet there is a seam. These seams are covered with mesh tape and then the seams and the screw heads are concealed with the drywall compound to make the wall seem as one uniform piece. The drywall plaster is a thick paste. Later this is painted or wallpapered over to hide the work. This process is typically called "taping" and those who use drywall are known as "tapers".
Main article: Plaster veneer
Veneer plastering covers the entire wall wiht thin liquid plaster, uses a great deal of water and is applied very wet. The walls intended to be plastered are hanged with "Blueboard" (named as such for the industry standard of the outer paper being blue-grey in color). This type of sheet rock is designed to absorb some of the moisture of the plaster and thus allow it to cling the plaster better before it sets.
Veneer plastering is a one-shot one-coat application; taping usually requires sanding and then adding an additional coat; since the compound shrinks as it dries.

Traditional Plastering
Main article: Plasterer
The plasterer usually shows up after the hangers have finished building all the internal walls, by attaching blueboard over the frames of the house with screws. The plasterer is usually a subcontractor working in crews that average about three veterans and one laborer. The job of the laborer is to set up ahead of and clean up behind the plasterers, so they can concentrate on spreading the "mud" on the walls.

Laborer's tasks
Debris left on the floors from the "hanging" crew must be removed before floor paper can be set down and to remove any tripping hazards.
Cover the floors with tar or brown paper since plaster can stain or be hard to remove from subflooring plywood.
Run hoses and extension cords and set up job lights.
Cover all seams with meshtape as well as any large gaps around outlets caused by poor roto-zip work. Gouge out any bubble in the wallboard caused by broken sheetrock under the paper and cover the holes with meshtape. Remove any loose screws left from the hanger missing the underlying frame.
Cover all windows and doors with plastic sheets and masking tape to protect the wood of their frames and save on cleaning. If any plumbing fixtures or wall plugs have been installed they are also covered, as well as the bathtubs and showers.
Set up for the next mix. As soon as the table is cleared the laborer is given instructions of how many bags will be needed as well as the next room to be worked in. The table typically consists of folding legs upon witch is set a square board of wood and then covered in a plastic sheet upon which the plaster is placed in the center in a large pile.
Mixing the product. The mixing barrel is usually pre-filled to a certain level with water; since it can take some time to fill. The amount of water is usually estimated (with a margin of error leaning towards too little). The amount of water required is obtained from the amount of bags planned to be mixed. The estimation is not difficult for an experienced plasterer; who knows how many sheets he can typically cover, and that one bag usually covers 2 & 1/2 to 3 sheets and 5 gallons of water is needed for one standard 50 pound bag. With a permanent crew that normally does the same amount per mix one can simply fill up the barrel to a known cut-off point.
Once the mix is set up and the plasterers are ready they instruct the laborer to start dumping the bags in the water barrel, while intermittently running the mixing drill. Once all bags are in the barrel more water is slowly added until the plaster is of proper consistency and is then thoroughly mixed. Before the mixing is completed, a margin trowel (or margin for short) is scraped along the inside wall of the barrel in order to knock off clinging unmixed clumps (known as cutting in) to be furthered mixed until all is homogeneous.
While mixing the drill is slowly brought up and down and follows the edge of the barrel in a circular motion in order to drag the top of the mix down and ensure an even consistency throughout the mix. Care is taken not to allow the drill's paddle to hit the bottom or sides of the barrel; this can scrape off plastic bits that end up in the mix. At a certain point before the mixing is done a margin trowel is again used to scrape any clinging dry plaster into the rest of the mix. typically this is when the accelerator; if used is added. Mixing can be fatigueing in that the drill tends to not only be heavy but the mixer must also fight the torc of the paddle.
Shovel the mix onto the table. The mixing barrel must be emptied as soon as possible, as the plaster will set faster in the barrel then on the table. but the table cannot be overfilled or it may tip or plaster will spill off the sides and splatter when it hits the floor. While shoveling care must also be taken not to splatter any plaster onto nearby walls.
Clean up the mix barrel. This is done outside with a hose and nozzle. If any plaster remains they can contaminate the next mix with "rocks" that greatly vex the plasterers as they get dragged across the walls and the contamination causes the plaster to set much quicker.
Final clean up. This includes rolling up all paper flooring in finished rooms. knocking the plaster out of plug outlet holes with a drywall hammer/hatchet, taking down any masking tape and plastic, cleaning up any plaster that has splattered onto the floor etc.

Plasterer's tasks
Normally the contractor has already supplied all the bags of Gypsum plaster that will be needed, as well as any external supply of water if the house is not yet connected. (Normally the type of plaster that is used is an industry standard called Uni-Kal. There is also another type not used as often called Kal-Kote; its finish is slightly different and not as bone white as Unical. The two products are distinguished by a color stripe across the top of the bag. Uni-Kal is rusty red, and Kal-Kote is purplish/maroon. The plastering crew needs to bring their own tools and equipment and sometimes supply their own bead.
The Tasks that the plasterer is usually expected to accomplish.
Hang cornerbead
The plasterer usually must first staple or tack Cornerbead onto every protruding (external) corner of the inside of the house. Care is taken to make sure this makes the wall look straight and is more of a skill of the eye then anything else.
"Bead" comes in many styles; Ranging from wire mesh attached by staples too heavier metal grades the need to be tacked on with nails. Plastic varieties also exist.
The bead must be measured and cut to size; care is taken not to bend or warp it. In places where more than one corner meets; the bead's ends are cut at an angle and the 2 or more tips are placed as close together as allowable; touching but not overlapping. The bead is completely covered with plaster as well as the rest of the wall and the plaster also helps to hold it firm. The finished product leaves only a small exposed metal strip at the protrusion of the corner which gets covered when the wall is painted. This leaves a clean, straight looking corner.
An alternative method seen in older houses of forming a rounded or bullnosed corner uses a quirked wooden staff bead. The staff bead, a 1 inch dowel with approx 1/3rd shaved off the back, is set on the external corner by the joiner on site, fastened to wooden plugs set into the brick/block seams, or to the wood frame. Plaster is run up to the staff bead and then cut back locally to the bead or "quirked" to avoid a weak feather edge where the plaster meets the bead.
In architecture a quirk is a small 'V' shaped channel used to insulate and give relief to a convex rounded moulding. To create the plastered corner, backing coat (browning) is plastered up to the staff bead, then the quirk is cut into the backing coat a little larger than the finished size. When the top skimming coat is applied, again the bead is fully skimmed in and then, using a straight edge, the quirk is re-cut to the finished depth, usually on an approximate 45 degree angle into the bead. The quirk will hide the eventual small crack that will form between the staff bead and plaster.
Sets up his tools
The plasterer needs to fill a 5-gallon bucket partway with water. From this bucket he hangs his trowel or trowels and places into it various tools.
Normally a plasterer has one trowel for "laying on" (the process of placing mud onto the wall).
Some then keep an older trowel that has a decent bend in it (banana curve) to be used for the purpose of "texturing"; if called for by the homeowner. A lay-on trowel tends to be too flat for this and the vacuum caused by the water can stick it to the wall, forcing him to tear it off and thus he has to rework the area.
Finally, one may have a brand new trowel "not yet broken-in" which he will used for "grinding"; this is when the plaster is nearly hardened and he is smoothing out any bumps or filling in any small dips to make the wall look like a uniform sheet of glossy white plaster.
Most plasterers have their own preference for the size of the trowel they use. some wield trowels as large as 20 inches in length but the norm seems to be a 16"x5". From my experience the preferred brand is a Marshalltown stainless steel. They have a brassy luster to them and won't pit or rust if accidentally left in water overnight.
Into the bucket also goes a large brush used to splash water onto the wall and to clean his tools, a paint brush for smoothing corners, and a corner bird for forming corners (though many share one good bird to keep the room harmonious).
These tool buckets are first kept near the mix table and then as the plaster starts to set are moved closer to the wall that is being worked on. Time becomes a big factor here as once the plaster starts to harden (set) it will do so fairly rapidly and the plasterer has a small margin of error to get the wall smooth.
Onto the mixing table the plasterer usually sets his "hawk" so it will be handy when he needs to grab it and to keep dirt off of it. Any debris in the plaster can become a major nuisance.
Plaster tops or bottom?
Plasterers will typically divide a room, (especially a large or high-ceilinged wall) into top and bottom. The one working on top will do from the ceiling's edge to about belly height and work off a milk crate for an 8-foot (2.4 m) ceiling, or work off stilts for 12-foot-high rooms. For cathedral ceilings or very high walls, staging is set up and one works topside, the others further below.
Clean up before they finish a job
Typically done with the laborer. No plaster globs left on the floors, walls or corner bead edges. (They will show up if painted and interfere with flooring and trim). Remove or neatly stack all trash.
Inspection
All rooms and walls are inspected for cracking and dents or scratches that may have been caused from others bumping into the walls. They are also inspected to make sure no bumps are left on the walls from splashed plaster or water. All rooms are checked to make sure all plaster is knocked out of the outlets so the electrician can install the sockets and to make sure no tools are left behind. This leaves the walls ready for the painters and finishers to come in and do their trade.

Interior plastering techniques


Smooth
The home owner and the plasterer's boss will usually decide beforehand what styles they will use in the house. Typically walls are smooth and sometimes ceilings. Usually a homeowner will opt to have the ceilings use a "texture" technique as it is much easier, faster, and thus cheaper than a smooth ceiling.
The plasterer quotes prices based on techniques to be used and board feet to be covered to the contractor or homeowner before work begins. The board feet is obtained by the hangers or estimated by the head subcontractor by counting the wallboards that come in an industry standard of 8' to 12' in length. He then adds in extra expenses for soffits and cathedral ceilings.
Ceiling second or first
Typically if the ceiling is to be smooth it is done first; before the walls. If it is to be textured it is done after the walls.
The reason for this is invariably when a ceiling is being worked on plaster will fall and splash onto the walls. However a texture mix doesn't need to be smoothed out when it starts to set;
thus a retardant such as "Cream of tartar" or sugar can be used to prolong the setting time, and is easily scraped off the walls.
and since time is not as restraining of a factor on textured ceilings a large mix, or back-to-back mixes can be done and all ceilings covered at the same time.
another reason is that a bird is usually run along the top corner after doing a smooth ceiling, then it is easier to maintain this edge by doing the wall last. But a textured ceiling normally doesn't need to be birded, only blended in with a very wet paint brush. In this case the wall is done first and the corner formed with the bird.
Scratching
The first thing the plasterer tends to do is go over all the mesh-taped seams of the walls he is about to cover; in a very thin swatch. The wallboard draws moisture out of this strip so when the plasterer goes over it again when doing the rest of the wall it will not leave an indented seam that needs further reworking.
He then fills in the area near the ceiling so he will not have to stretch to reach it during the rest of the wall; And he forms the corner with his bird. This saves much needed time as this process is a race against the chemical reaction.
Laying on
From the Mix table the plasterer scoops some "mud" onto the center of his hawk with his trowel. Holding the hawk in his off-hand and his trowel in his primary the plasterer then scoops a bulging roll of plaster onto his trowel. this takes a bit of practice to master, especially with soupy mixes.
Then holding the trowel parallel to the wall and at a slight angle of the wrist he tries to uniformly roll the plaster onto the wall. In a manner similar to a squeegee. He starts about an inch above the floor and works his way upwards to the ceiling. Care is taken to be uniform as possible as it helps in the finishing phase.
Knocking down
Depending on the setting time of the plaster. once the moisture of the plaster starts to be drawn by the board a second pass is made. this is called knocking down. it is much like applying paint with a roller in wrist action and purpose. to smooth out any lines and fill in any major voids that will make extra work once the plaster starts to truly set. very little pressure is applied and the trowel is kept relatively flat towards the wall.
Setting
Sometimes an accelerant will be added to a mix to hasten the time delay from the initial mixing phase to when the plaster starts to set. This is normally done on cold days when setting is delayed or for small jobs to minimalize the wait.
Once the plaster is on the wall and starts to set (this can be determined by the table that sets first); the plasterer gingerly sprinkles water onto the wall, this helps to stall the setting and to create a slip. He then uses his trowel and often a wetted felt brush held in the opposite hand and lightly touching the wall ahead of the trowel to work this slip into any small gaps (known as "catfaces") in the plaster as well as smooth out the rough lay-on and flatten any air bubbles that formed during setting.
This is a crucial time because if the wall gets too hard it is nearly impossible to fill in and gaps as the slip will no longer set with the wall and will instead just dry and fall out. This leads to the need of what is called "Grinding" as one must go over the hard wall again and again trying to smooth out the hardened wall and any major catfaces must be filled in with a contour putty, joint compound, or reworked by blending in a fresh, thin coat.
The finished wall will look glossy, Uniformly flat and is smooth to the touch. After a few days it will become chalky white and can then be painted over.
Mix
From the time the bags are dumped into the barrel to when the wall is completely set is called a mix. Varying on the technique used and whether accelerant or retardant is added, a mix typically lasts about two hours.
The final moments are the most frantic if it is smooth or if the mix sets quicker than anticipated. If this happens it is said the mix has "snapped" and is normally due to using old product or various types of weather.(humidity or hot days can cause plaster to set quicker) Normally only 3 or four mixes are done in a day as plastering is very tiring and not as effective under unnatural lighting in the months with early dusk.
Seasons
Plastering is done year round but unique problems may arise from season to season. In the summer the heat tends to cause the plaster to set faster. The plaster also generates its own heat and houses can become quite hellish. Typically the plaster crew will try to arrive at the house well before dawn.
In winter months short days causes the need of artificial lighting. At certain angles these lights can make even the smoothest wall look like the surface of the moon. Another dilemma in the winter months is needing to use propane jet heaters (which can stain the plaster yellowish but does not otherwise hurt it), not just to keep the plasterers warm but to also prevent the water in the mix from freezing and generating ice crystals before the plaster has time to set. Also if the water hose is not thoroughly drained before leaving it can freeze over night and be completely stopped up in the morning.

Textured
Texturing is usually reserved for closets, ceilings and garage walls.
Typically a retarding agent is added to the mix. this is normally "Cream of Tartar (or "Dope" in the plasterer's jargon) and care must be taken with the amount added. Too much and the mix may never set at all. However the amount used is often estimated; much the way one adds a dash of salt to a recipe. you add a small scoop of retarder, dependent on the size of the mix. Retardant is added so that larger mixes can be made, since the texture technique doesn't require the person to wait until it starts to set before working it.
The lay-on phase is the same as smooth but it is added with a thicker coat. Once the coat is on uniformly the plasterer then goes back and birds his corners. Staying away from the corner he then gets a trowel with a nice banana curve in it and starts to run it over the wall in a figure eight or Ess pattern, making sure to cross all areas at least once. He adds a little extra plaster to his trowel if needed. The overall effect is layers of paint-like swaths over the whole of the ceiling or wall. He can then just walk away and let it set with care taken not too leave any globs and to make sure the corners look smooth and linear.
If a wall is to be smooth and the ceiling textured, typically the wall is done first, then the ceiling after the wall has set. Instead of rebirding the ceiling (which would have been done when the wall was laid on), a clean trowel is held against the wall and its corner is run along the ceiling to "cut it in" and clean the wall at the same time. This line is then smoothed with a paintbrush to make the transition seamless.

Sponge
The sponge (technically called a float), has a circle form and rough surface. it is fixed to a backing with a central handhold and is roughly the size of a standard trowel. Sponge is a variant texture technique and used normally on ceilings and sometimes in closets. Typically when using a sponge; sand is added to the mix and the technique is called sand-sponge.
Care must be taken not to stand directly under your trowel when doing this as it is very, very unpleasant, and dangerous to get a grain of sand in your eye; which is compounded by the irritation from the lime as well. This combination can easily scratch the eye.
The lay-on and mix is the same as with regular texturing. however after a uniform and smooth coat is placed on the ceiling and the edges are cut in; a special rectangular sponge with a handle is run across the ceiling in overlapping and circular motions. This takes some skill and practice to do well.
The overall look is a fishscale type pattern on the ceiling, closet wall, etc. Even though retarder is typically used; care must be taken to clean out the sponge thoroughly when finished as any plaster that hardens inside it will be impossible to remove.

Ceilings
Stilts are often required to plaster most ceilings and it is typically harder to lay-on and work then walls. For short ceilings one can also work off of milk crates. The difficulty of working upside down often results in plaster bombs splattering on the floors, walls and people below.
This is why smooth ceilings, that use no retardant and sometimes even accelerant, are done before the walls. Retarded plaster can easily be scraped off a smooth plaster wall when wet. Any splatters from a smooth ceiling can easily be scraped off bare blueboard but not from an already plastered wall. Care must be taken when standing under your trowel or another plasterer.
The general difficulty of working a smooth ceiling fetches a higher cost. The technique is the same as a smooth wall but at an awkward angle for the plasterer.

Tools of the trade
Broom
Bucket trowel
Cornerbead
corner bird
Display bird-can be set for wider then 90 degree angles
Drywall Hammer or Drywall Hatchet -- use to clear plaster globs out of plugholes.
extension cords
5 gallon buckets-for tools, washing, steps/stools, for small patch mixes, lugging plaster onto staging etc.
Floor scraper -- Optional
Gauging trowel
Halogen work lights
Hawk (plasterer's tool)
High RPM mixing drill with appropriate paddle
ladders and a few 6x4 planks-supplemental
masking tape -- for window panes and door jambs
mesh tape--multiple rolls
Milk crate -- used to store tools and as stools
Multi cord outlet
Pipe Staging-supplemental
Plastic 30 to 50 gallon drum-For mixing, often obtained from car washes
putty knife --supplemental
Scoop -supplemental-- to remove plaster from a bucket
Shovel -- short handled, is used to load the table with plaster mud.
soft bristle paintbrush -- for smoothing edges and corners
Trowels--various sizes and levels of breaking-in (cost avg $60)
Margin Trowel or margin for short—for edging the mix barrel
Spat or spatula trowel
sponge (tool)/Float
Staple gun -- for corner bead
table stand and a table board
tar paper or brown paper rolls—tar paper offers more water protection and is a bit more resilient but is costlier to use.
roll of plastic sheeting
Uni-Kal -- a gypsum based plaster that comes in 50 pnd bags.
Kal-Kote -- an alternate brand with a slightly less glossy finish
DIAMOND Basecoat -- used in cases where cracking is suspected to occur, deep fill-ins
Utility knife--to cut plastic sheeting for table boards and floor covering paper
Water hose and nozzle
Water brush – large, for cleaning tools and splashing walls