User:Bāḏinjān/sandbox/Plaster

Plaster

Gypsum

[...]

General instructions for preparation and use

While the precise details of how to prepare plaster will vary according to the formulation used, desired qualities and applications, the basic process is the same.

Before mixing

Once the process of mixing has begun, the chemical reactions will occur swiftly so there will not be time to get anything ready.

1. Consult manufacturer's instructions and/or experienced users to determine
   1. safety instructions and requirements
   2. acceptable ambient temperature for use
   3. water/plaster ratio
   4. water temperature: the product documentation will provide a range; in general, warmer temperatures hasten cure and cooler slows it down
   5. soaking time
   6. mixing time
   7. length of plasticity
   8. time til cure
   9. any other special instructions
2. Determine the required quantity of plaster. For many applications, the quality of the end product will be severely compromised if insufficient plaster is mixed in the first attempt and a second batch is made to complete it. Because plaster solidifies by curing, it will be uneven and therefor structurally unsound. It is better to mix more than required by about 10%.
3. Measure the plaster and water. Measuring by weight is preferable to volume, if possible, because plaster can settle and volume may be inconsistent. Some users of plaster do not measure the dry component in advance but instead make use of visual and tactile judgement to decide when an appropriate mix has been achieved. This method is not discussed here.
4. Ensure all required materials, tools, containers and protective equipment are available. See Safety Issues, below. Mixing containers and tools must be completely clean. Equipment which has been used for previous batches must be carefully inspected to ensure no cured plaster remains as the presence of this can alter the curing process and therefor compromise the finished product of the new batch.
5. Plan for clean up before beginning to mix and make sure everything is available. (See Clean Up, below.)
6. Prepare the intended destination for plaster once mixed, be is a mold, wall, sculpture, medical application or other. Some materials require use of a releasing agent, of which there are a wide variety depending on application.
7. Prepare the work environment: Plaster can be difficult to impossible to remove from porous surfaces, especially textiles but also wood, some tile etc. Drop cloths or other protection should be used if random dollops of plaster are not desired as permanent decorative features of the environment. Any clothing worn for this process risks plaster damage.

Mixing

1. Place correct quantity of water in the mixing container.
2. Add plaster by sifting slowly into the water. Do not dump the plaster by handfuls or all at once. Do not mix at this point, simply let it drop into the water.
3. Continue adding all the dry plaster which is needed. It is not possible to add more later as curing will be uneven so everything needs to be added at once.
4. Let the plaster soak without mixing it for the appropriate amount of time. This will usually be from 1 to 10 minutes. Use of a timer is advised for precision.
5. Mix for the appropriate amount of time. Again, a timer might be helpful here. Mixing time affects the properties of the plaster both in its liquid stage and in the final product. Depending on preferences and application, mixing can be done with a tool such as mixing stick (small batches only), by gently circulating one's gloved or bare hand in the mix, or with a special attachment on a drill. Whatever method is used, care should be taken to avoid introducing air bubbles by agitation or repeated removal and reinsertion of mixing implement. The mixing container can be tapped, knocked, or vibrated to encourage any air bubbles to rise to the surface.
6. Mixing is generally concluded once the consistency is similar to thick cream.
7. If the application involves pouring, this should be done with alacrity. The plaster will soon begin to thicken and any delay will lead to excessive air bubbles.

Pouring or application

1. Prior to pouring, it may be helpful to tap or vibrate the mixing container to further release any air bubbles.
2. Pour slurry into a prepared mold by slowly allowing it to drip into the deepest area. Do not move the mixing container to spread the plaster around, rather allow gravity to do this. Again, tapping on the mold will facilitate the movement of plaster into all nooks and crannies and hopefully minimize bubbles.
3. Once it begins to cure, it is generally inadvisable to handle or manipulate plaster unless there is specific a technique which requires this. Disturbing plaster which has begun to cure will compromise the integrity of the final product.

Curing

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Clean up

Plaster should never be washed down the drain or the toilet. Even the plaster which comes off one's hands can collect and solidify in the plumbing. There is no way to remove plaster from pipes and if this happens they must be removed and replaced at the expense of the owner. For this reason it is critical to consider the methods of cleaning before beginning.

Hands, tools, clothes, mixing containers and all other contaminated items must be carefully cleaned by one of two methods:

Rising immediately

This is the preferred method for hands and items which are not suitable for the other method, but anything else can be done this way as well, providing a large enough bucket is available.

1. Wet plaster can be rinsed off in a bucket specially designated for this purpose.
2. After use, the water is allowed to sit for some time. The plaster will settle to the bottom and the majority of the water, which is clear, can safely be discarded.
3. The sludge at the bottom can either be disposed of somewhere other than plumbing if that is available, or it can be left uncovered for a few days. Eventually the water will evaporate, leaving only solid material which can be disposed of in the trash.

Allow plaster to cure and knock it off later

1. Implements are simply left covered in plaster after use.
2. Plaster should not be scraped off prior to leaving them. In fact, the thicker the residual plaster, the easier it will be to remove later. Thin layers of plaster will be flaky and potentially tedious.
3. Once cured, plaster is simply cracked and falls off easily.

Items suitable for ============================

External links

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