Recent Projects and Photos by Bestwall Plastering
The Art Of Plastering Featuring Work Performed By Bestwall Plastering
What type of plaster should you use?
Plastering is a process used to produce an acceptable final wall or ceiling finish to a building prior to decoration. A substrate is the surface to which the plastering system is to be applied. Backing coats which cover the substrates are between 9mm and 40mm thick under normal circumstances and the overall thickness can be built up in coats as is necessary.
Ceilings and Partitions
In older building, these areas are covered in a layer of timber laths which are plastered over. When strength is required, a thin steel sheet mesh called expanded metal lath is fixed in place and then plastered over. In contemporary fast-track work plasterboards are fixed in place, the joints taped with a fibre mesh tape (scrim) to prevent cracking and then skimmed over with a finishing coat of a gypsum plaster.
Basic plasterboard is a flat sheet of gypsum between 9mm and 12.5mm thick, sandwiched between sheets of durable paper. Boards are also available with various backings of differing thickness to improve insulation, restrict the passage of water vapor and to protect against fire. It has become common practice to bond or fix plasterboards to substrates to serve as the backing plaster coat. This method is known as dot and dab or drywall.
Finishing coats are usually between 3mm and 5mm and bring the backing coats to a smooth skim finish. Finishing plasters used to produce these setting coats are available as premixed gypsum plasters. Finishing coats can also be lime putty and fine sand or a mixture of lime, sand and gypsum known as gauged setting stuff.
Solid plastering denotes backing coats of a paste or mortar-type consistency comprised of an aggregate and a binding matrix. Binders include lime, gypsum and cement. Aggregates include sand, vermiculite and perlite.
Choosing a Plastering Material
Lime plasters are compatible with old buildings containing slight dampness. They are said to breathe, which means they allow moisture to evaporate from the wall before it shows as damp patches. It is always worth considering why moisture is present in the wall in the first place?
Gypsum plasters set much quicker than lime plasters, so speed up waiting times between coats. In cold conditions gypsum backing plasters can take a long time to dry. Gypsum backing plasters (and this includes standard plasterboards) should never be used on damp walls. Gypsum plasters are compatible with dry brickwork or blockwork, preferably to internal surfaces of cavity wall construction.
Cement-based plasters or renders have their uses, they can be gauged with lime and used externally, and can be useful for waterproofing and tanking. Strong mixes can pull away from weak backgrounds and are brittle – cracking if slight movement of the building occurs, they can also be cold and attract condensation.
Decorative plasterwork has a long history. Mouldings were originally run in-situ with ornaments cast in carved boxwood, pear-wood or hard plaster and gelatine moulds using composition materials and gauged setting stuff. At a later date fibrous plastering techniques arrived, first used in France, the technique involves the use of Plaster of Paris with hessian/canvass scrim to reinforce casts and timber laths to assist fixing. With some timber, sheet steel, moulding compounds and a few bags of casting plaster, all manner of ornamental plasterwork can be created.
What Is A Plasterer?
The Plasterer is a skilled craftsman who can spread plastering materials over a *substrate* producing a finish as required by the client.
Although plaster can be projected onto walls with pumps or sprays and one-coat plasters are available, most high class work still applied by the plasterer using hand tools in 3 coats consisting of a scratch coat to even out suction, a float coat to give an even surface and a finishing coat to produce a smooth finish.
*The word substrate comes from the Latin sub - stratum meaning 'the level below' and refers to any material existing or extracted from beneath the topsoil, including sand, chalk and clay. The term is also used for materials used in building foundations or else incorporated into plaster, brick, ceramic and concrete components, which are sometimes called 'filler' products.
How Many Coats Of Plaster Do You Need?
Plaster Coats (How Many Layers) - Plaster is applied in successive coats or layers on walls or lathing and gains its name from the number of these coats.
- One coat work is the coarsest and cheapest class of plastering, and is limited to inferior buildings, such as outhouses, where merely a rough coating is required to keep out the weather and draughts. This is described as render on brickwork, and lath and lay or lath and plaster one coat on studding.
- Two-coat work is often used for factories or warehouses and the less important rooms of residences. The first coat is of coarse stuff finished fair with the darby float and scoured. A thin coat of setting stuff is then laid on, and trowelled and brushed smooth. Two-coat work is described as render and set on walls, and lath, plaster and set, or lath, lay and set on laths.
- Three-coat work is usually specified for all good work. It consists, as its name implies, of three layers of material, and is described as render, float and set on walls and lath, plaster, float and set, or lath, lay, float and set, on lathwork. This makes a strong, straight, sanitary coating for walls and ceilings.
The process for three coat work is as follows:
- For the first coat a layer of well-haired coarse stuff, about 1 inch thick, is put on with the laying trowel. This is termed "pricking up" in London, and in America "scratch coating". It should be laid on diagonally, each trowelful overlapping the previous one. When on laths the stuff should be plastic enough to be worked through the spaces between the laths to form a key, yet so firm as not to drop off. The surface while still soft is scratched with a lath to give a key for the next coat. In Scotland this part of the process is termed "straightening" and in America "browning", and is performed when the first coat is dry, so as to form a straight surface to receive the finishing coat.
- The second or "floating coat", and is 1/4 to 3/8 inches thick. Four operations are involved in laying the second coat, namely, forming the screeds; filling in the spaces between the screeds; scouring the surface; keying the face for finishing.
- Wall screeds are plumbed and ceiling screeds leveled. Screeds are narrow strips of plastering, carefully plumbed and leveled, so as to form a guide upon which the floating rule is run, thus securing a perfectly horizontal or vertical surface, or, in the case of circular work, a uniform curve.
- The filling in, or flanking, consists of laying the spaces between the screeds with coarse stuff, which is brought flush with the level of the screeds with the floating rule.
- The scouring of the floating coat is of great importance, for it consolidates the material, and, besides hardening it, prevents it from cracking. It is done by the plasterer with a hand float that he applies vigorously with a rapid circular motion, at the same time sprinkling the work with water from a stock brush in the other hand. Any small holes or inequalities are filled up as he proceeds. The whole surface should be uniformly scoured two or three times, with an interval between each operation of from six to twenty-four hours. This process leaves the plaster with a close-grained and fairly smooth surface, offering little or no key to the coat that is to follow.
- To obtain proper cohesion, however, a roughened face is necessary, and this is obtained by keying the surface with a wire brush or nail float, that is, a hand float with the point of a nail sticking through and projecting about 1/8 inch; sometimes a point is put at each corner of the float.
- After the floating is finished to the walls and ceiling, the next part of internal plastering is the running of the cornice, followed by the finishing of the ceiling and walls.
- The third and final coat is the setting coat, which should be about 1/8 inch thick. In Scotland it is termed the "finishing coat", and in America the "hard finish coat" or "putty coat". Setting stuff should not be applied until the floating is quite firm and nearly dry, but it must not be too dry or the moisture will be drawn from the setting stuff.
The process for three coat work is as follows:
- The coarse stuff applied as the first coat is composed of sand and lime, usually in proportions approximating to two to one, with hair mixed into it in quantities of about a pound to two or three cubic feet of mortar. It should be mixed with clean water to such a consistency that a quantity picked up on the point of a trowel holds well together and does not drop.
- Floating stuff is of finer texture than that used for pricking up, and is used in a softer state, enabling it to be worked well into the keying of the first coat. A smaller proportion of hair is also used.
- Fine stuff mixed with sand is used for the setting coat. Fine stuff, or lime putty, is pure lime that has been slaked and then mixed with water to a semi-fluid consistency, and allowed to stand until it has developed into a soft paste.
- For use in setting it is mixed with fine washed sand in the ratio of one to three.
- For cornices and for setting when the second coat is not allowed time to dry properly, a special compound must be used. This is often gauged stuff, composed of three or four parts of lime putty and one part of plaster of Paris, mixed up in small quantities immediately before use. The plaster in the material causes it to set rapidly, but if it is present in too large a proportion the work will crack in setting.
The hard cements used for plastering are laid generally in two coats, the first of cement and sand 1/2 to 3/4 inches thick, the second or setting coat of neat cement about 1/8 inch thick.
The Wall Street Journal Article
Historic Remake: If These Walls Could Talk, They'd Say "Plaster, Please"
I had walls that were cracked and chipped. Nothing makes an old house feel old and decrepit like cracked and bumpy walls. But transforming walls from drab and dreary to bright and cheerful isn’t difficult. It’s messy, but not complicated.
When I began the renovation on my 85-year-old Tudor revival-style house, updating and repairing the walls was first on our list. Like most old homes built before World War II, my walls are made of plaster, not the drywall found in most post-WWII homes. Preservationists insist that plaster is a better product than modern drywall. After all, plaster has stood the test of time. Archeologists say that lime plaster was used as a type of mortar in Egyptian pyramids.
Plaster is a mud-like substance that, when it dries, leaves a hard surface that is smooth to the touch, keeps firm for many decades and holds sound better than drywall. That’s good for parents who don’t want conversations in the master bedroom overheard by the kids in the next room.
This is the same area after two skim coats, but before painting.
Plaster is also less susceptible to mold, which was a big problem in my kitchen, the only room in my house that had drywall. (More on that in a later column.)
For a more high-end affect, some plasterers add marble dust to the mixture, which leaves an even harder wall finish that can be made to resemble the marble or granite walls found in historic Italian palazzos. (Some call this Venetian plaster, not to be confused with faux Venetian plaster that some paint companies sell). Drywall is made from gypsum wrapped in cardboard. It comes in large pre-made wall-size boards that are screwed or nailed in place. Even though drywall is considered a lower-end product than plaster, it has a major benefit: it’s much easier and less expensive to install.
"For every 500 guys who do drywall, you can find only a few who can do plaster," said Kieran Quilligan, president of Bestwall Plastering Inc. in New York. If the plaster repair job includes intricate crown molding, that’s even a rarer skill that only a small number of plasterers can manage. While the Internet is filled with debates about which wall construction is better, most specialists believe that both are good products for the right job. “Drywall for modern structures, it’s modular and fits into that scheme beautifully,” said Rory Brennan, chief executive of Preservation Plastering Ltd. in Brattleboro, Vt. “Old houses have their own set of rules predicated upon the materials and techniques used to build them.” Mr. Brennan provides plastering advice to the television program, “This Old House."
I had just one plaster wall that needed to be replaced. Here it is after the work. Yet preservationists say too many owners of old homes are tearing out their plaster and replacing it with drywall.
Not me. I took great pains to repair plaster, although I used a less expensive plastering method. The die-heart preservationists prefer that plaster walls are repaired or replaced using the most historically accurate — and most expensive — method, which is a three-coat system that requires a skilled plasterer to actually re-build the wall from the laths. A faster method is to install blue board over the laths and cover the boards with a plaster veneer.
The least expensive method, which works well on walls that aren’t badly damaged, is a simple skim coating, where a layer of plaster, sometimes combined with joint compound or spackle, are layered over the entire wall and sanded smooth.
Lucky for me, I had only one plaster wall — above the bay windows in the master bedroom — that needed to be replaced. For that, Edgar, my contractor, used the blue board system. But the remaining walls were just badly cracked and chipped, which was easily addressed by receiving two skim coats. The end result was better than I expected. The walls are beautiful, rock hard and have a slight shimmer. When painted, they were somewhat luminescent.
My delight at the results helped lessen the pain of the job itself, which was by far the messiest portion of my home renovation. It also took longer than any other job to complete and created loads of dust. From start to finish, it took four weeks to complete most of the house, at a cost about $200 a day. But the results are so pleasing that I can’t complain.