Not so long ago interior walls were built by nailing 4' long strips of wood horizontally over the studs about 1/4" for each course. These strips were 1- 2" wide and 1/4" thick and meant to hold a primary layer of plaster to close off the wall. A plaster applies the mix of sand-heavy paster called a "brown coat" to cover the lath and to provide a good base for the finish coat. With a steady application the brown coat will be forced through the spaces between the lath and for a solid reinforcement. This is called "keying" and the plaster blobs between the slats called "keys." A smooth white coat is then troweled over the base coat, or coast, and the wall is ready for painting or wall-papering.

Types of Drywall

Sheet Rock

The invention of gypsum board revolutionized the way interior walls were formed. This is also called "sheet rock" and is made by squeezing the wet gypsum mix through thick paper sheets. When dried into 4 X 8 foot sheets this can be fastened to interior studs spaced at 16" apart. Besides speeding up the interior wall process it is vastly less labor-intensive than plastering. In the past it took a crew 2-3 weeks to lath and plaster a home whereas drywalling will take 1 day to install and 2 more to tape and finish.

When manufacturing the core of the drywall sheet the wet gypsum plaster is mixed with a paper or fiberglass fiber for strength, a foaming agent and potash. Depending on what type of drywall is being made, and for what area, there are various strengths of mold and mildew inhibitors as well. When dried the sheets are usually the norm 4 X 8 foot ones but with the higher ceilings in the new homes sheets are made both 9' and 10' long. In commercial uses it is not rare to see 12' sheets.

Green Board

When drywalling bathrooms and basement areas which have a high moisture content the drywaller will use green board. Green board drywall is similar to regular sheet rock except the paper coating is waterproof and the color is green. Although it is used in bathrooms it should not be used as a backing for tile. A cement board should be placed over the green board for that. As well, like all other drywall it should never be used in direct contact with water as it will breakdown and get moldy like regular drywall. In addition is is not as fire resistant or durable as regular drywall.

Blue Board

Like green board and drywall blue board is made with the same gypsum mix and comes in similarly-sized sheets. The difference, besides being a blue color, is the paper covering which is a special covering designed to accept and hold a skim coat of plaster. In other words blue board actually takes the place of lath and the brown coats of plaster so that the wall can be as smooth and hard as when the pasterers were around doing all the homes.

This process is called "veneer plastering" and the result is a wall that is smoother and harder than regular drywall. In fact screws and joints never show through a good application and the wall will resist dents and imperfections associated with the regular taping jobs. In addition plaster may not be painted. It can stay the bright white or tinting can be applied into the mix so that the color goes on as the plaster is being done. A design coat can also be applied, especially to ceilings.

Cement Board

Cement board is a mix of cement and fiberglass fibers which are rolled into a sheet. Unlike drywall and its derivatives cement board does not need paper reinforcing sheets on each side to maintain its integrity. Despite its hardness it can accept nails and screws for attaching to studs, floors and walls but the holes, in most cases, should be pre-drilled.

Because of its resistance to water, mold and mildew cement board is used as a backing for tiles in showers, kitchens and basements. Unlike green board it will not break down after time when exposed to water. The downside of cement board is that it's heavy and has to be cut with a special carbide-tipped saw. However, it is the standard for work where plumbing and extreme heat is nearby, such as behind a wood stove.

The Future of Plastering

Plastering is not a lost but there are fewer tradespeople who do is anymore. Many moldings once created with the hands of professionals are now being molded and attached. However, this is not to say that you cannot get someone to do the finishing touches once the drywalling company has left. For a good drywalling or veneer plastering job it is advisable to consult with a drywalling installer or plaster company.