iPlaster on Traditional Plastering

                                            "Three Coat Plaster & Veneer Plaster"


Three-Coat Plaster :


Plaster must be applied in such a way that it adheres to the support surface, bears its weight load without cracking, and exhibits a smooth, hard, finished surface suitable for painting or papering. A quality plaster job begins with the lath on which the plaster will be applied. Traditional lath and plaster jobs used wood lath, but the moisture level in wood makes it expand and contract, which can make plaster crack. Metal lath is a more reliable surface for plastering since it does not retain moisture and provides more “keys” or spaces in its surface for proper adhesion.  Interestingly, metal lath was just coming into popularity in the United States at the time this building was constructed.


The three-coat plaster system begins with two coarse or rough coats. These coats form the base of the wall and are mixed of lime or gypsum, aggregate, fiber, and water. Sand is the most common aggregate used in rough-coat plaster. The lime is typically derived from limestone or ground oyster shells. Many firms now work with gypsum since it eliminates the need for added fiber and has a much quicker set up and drying time. Boro works with a ratio of three-to-one, bags of sand to bags of gypsum, for their rough coats.


The first coat is called the scratch coat and is applied at 3/8 inch thick then scratched or scored with a comb to give it a rough texture. The second rough coat is made of the same mixture and is called the “brown coat.” The brown coat is applied directly to the scratch coat, also at a 3/8-inch thickness, but left unscored. The sand provides a rough texture that gives the light, 1/8-inch finish coat a surface to grip onto.




Everyone knows drywall and you can’t beat its cost. But almost no one loves drywall, a leading cause of contractor callbacks for problems like popped screws and nails, dents and dings, visible joints, and paint problems  —quality issues that are addressed by blueboard.

Blueboard has many similarities to regular drywall gypsum board: Like drywall, it comes in 4-foot-wide boards at lengths of 8, 12, or 16 feet; it cuts with a knife; and it fastens to wood or steel wall studs with screws or nails. It also has the same core material: Gypsum, known to chemists as calcium sulfate.

The difference is in the paper covering: blueboard's characteristic blue face comes from the special paper on the board's surface, which is treated to bond well to a skim coat of specially formulated plaster. When finishing blueboard, instead of applying several coats of joint compound to the seams between boards, a quick tape-and-plaster treatment to the joints is applied, and then the entire wall surface is covered with one or two thin (1/8 inch thick) coats of plaster. A skim coat of plaster can be applied to regular drywall or an existing traditional plaster surface, but first the wall must be painted with a specially formulated orange-colored primer.

Veneer Plaster Advantages

Blueboard and veneer plaster offer two advantages over ordinary drywall — quality and convenience. Veneer plaster is much harder than a regular drywall surface, making it less likely to get unsightly dents and scratches. The top surface of plaster veneer is continuous over the whole wall, so joints almost never show at all—and certainly never leap out at the eye the way drywall joints commonly do. Veneer plaster's continuous surface is also a better base for paint. On a drywall surface, paint can dry differently on the paper surface than on the joint compound base at drywall seams. Even the most skillfully made drywall joints may show up in certain lights. Veneer plaster is much less likely to display any sort of visible shading difference.

Painting veneer plaster is not required. Some people are happy with the plaster's own natural off-white color, and consider the plaster's smooth surface sufficient. It's also possible to colorize the plaster coat itself, either by adding a high-quality paint to the plaster at the mixing stage, or by using proprietary
coloring systems.


                                                     " We Plaster at iPlaster "