All Purpose Type
All purpose skim coat plaster is typically a base coat for a damaged wall. A worker trowels the plaster against the wall, spreading the compound uniformly for covering any cracks or fissures. A second coating, with a different plaster type, usually applies on top of the all purpose. However, the first coat must dry completely before a second coat can adhere correctly. Do not use all purpose plaster for a second, or top, coat. It is difficult to sand and shrinks during the drying process.
Quick Set Type
A quick set skim coat plaster is another option for a base coat. The plaster, also known as chemical setting, is in powder form. A worker must add water to the powder and mix thoroughly. The chemical reaction between the powder and water creates a drying time of between five and 210 minutes. A worker must apply the plaster quickly and accurately since the plaster will continue drying until hard. Once hardened, the surface is difficult to sand down.
Topping skim coat plasters offer less shrinkage than both all purpose and quick set, as well as an easily sanded top surface. Topping application requires one or two coats, depending on the worker's surface smoothing skills with a trowel. After the topping dries, a worker sands the surface and applies a primer, readying the area for a new paint coat.
Some homes use skim coat plaster over a blueboard gypsum surface, as opposed to standard drywall. Though more expensive for installation, skim coat plasters offer a practically perfect finished wall surface. Sounds within the room are isolated. Any abuse to the wall, such as an impact, are easily resisted, compared to drywall systems.
Drywall School recommends topping off a bucket of skim coat plaster for use on another day. Typically, all plaster must be applied immediately after mixing, or opening, the container since the compound will begin drying. However, topping the surface of the plaster with a few inches of water preserves the compound below. Verify that all of the plaster is below the waterline and not dripping down the plaster container's inside walls.