How to Apply Stucco
Stucco is an ancient way of covering a wall to weatherproof it using a kind of cement made from Portland cement, fine sand and powdered lime that makes it easier to spread. The stucco is applied to the wall onto special lathes that in their modern form look like chicken wire standing out from the wall by using special nails that have a washer that it between the wall and the wire. The stucco is applied in three layers. Although it is usually applied over wooden walls it can also be used over rammed earth, straw or concrete construction.
The first step is to prepare the walls by cleaning them if necessary then applying the lathe with special nails with washers that are called “furring nails.” The wire goes between the head of the nail and the washer so it is standing out from the wall a fraction of an inch. At this point the wall is ready to receive the first layer of stucco.
The first coat of stucco is called the scratch coat and is applied from the top down in a layer about a quarter of an inch thick. The layer is applied using conventional mason's tools like a trowel. While this layer is still reasonably soft its surface is worked over with a tool that looks like a small rake called a scarifying tool so that the layer is covered with a series of scratches to hold the next layer.
The next layer is called the brown coat because it used to be made by using a brown sand so you could easily see that the coverage was complete, and also see if the finish coat completely covered the brown layer. This layer is applied over the scratch layer about 1/8 to ½ inch thick. The thicker layer covers any irregularities better then a thin one.
The finish coat is applied over the brown coat using a mason's trowel in a layer about 1/8 inch in thickness. This layer can be either left smooth like plaster or it can be worked with various tools to attain a textured appearance. The use of a sponge on its surface leaves a knobby appearance to the stucco. Other devices leave different appearances.
For small jobs you can buy bags of premixed stucco of if your job is larger you can mix the different layers of stucco from bulk ingredients. Stucco is composed of Portland cement, fine sand, powdered lime and enough water to make it easily spread. Although is isn't necessary the brown coat should be a contrasting color to the other two coats, so you can see what you're doing.
A great deal of grief can be avoided in applying stucco by paying attention to the weather conditions especially if the temperature is +80 F or below +40 F. Above +80 F the stucco will dry out to soon and crack. Below +40 F the stucco won't set properly. You shouldn't try to apply stucco in the rain. It also should be applied when the sun isn't beating directly on the surface of the stucco as this will also cause the stucco to dry out and become cracked.
The best base you can use for stucco is ¼ to 3/8 inch plywood covered with a layer 15 lb. Builders felt or kraft paper before applying the lathes. The way you trim windows and doors is by using a product called stucco or brick mold available at a building supply store.
Stucco should never be allowed to touch the ground because it will pick up moisture that will eventually destroy the lower edge of the stucco. There is a product called a stop bead that is also a weep screed that is applied to the bottom of a coating of stucco preventing it from coming into contact with the ground. Stop bead comes in ten foot lengths that is installed before the lathes are installed.
Be sure to carefully read any instructions that come with any of the products before you try using them. This will keep you from falling victim to any grief caused by not reading the directions first!
Stucco, Ortho Home Improvement Encyclopedia, Ortho Books, 1985, pages 382 – 387
Stucco, Wikipedia, http://en.wikipedia.org/wiki/Stucco