Summary: For most plaster uses, whether it be for patching or repairs, or building an entire plaster wall, modern wall plaster can be purchased as a dry pre-mix that you just add water to, and perhaps an aggregate or a fiber ingredient, if desired. But if you want to know how to make wall plaster yourself, here are some historical and traditional considerations.
Safety First
Always be sure to take standard precautionary safety steps when working with the powdered ingredients of plaster and make sure you have the following safety items available for your protection: safety glasses, gloves, and a proper dust mask or respirator. Pollen masks or surgical masks are not designed for the fine gypsum dust particles that you will need to protect yourself from
Lime Plaster or Hide Plaster
Back in the old days, up until the 1900’s, plasterers traditionally mixed bags of quick lime with water. As the lime absorbed the water, heat was given off. When the mix finally cooled down, and the lime and water were thoroughly mixed, the lime putty that resulted was used to make plaster with fine sand or marble dust (aggregate) and animal hair (fiber) mixed in along with some more water. Depending on if it was to be a base coat or a finish coat, the amount and kind of aggregate and fiber varied. A small amount of plaster of Paris was often added to speed up the setting time, but it still could take up to a year to dry.
Gypsum Plaster
Around 1900, gypsum was starting to be used as a plastering material because it begins to cure as soon as it is mixed with water and it sets in minutes. It is completely dry within two to three weeks. Gypsum creates a more rigid plaster and does not require a fiber binder. However it is hard to tell the difference between lime and gypsum plaster once the plaster has cured unless you can find the animal hair.
However, gypsum plaster is more vulnerable to water damage than lime plaster and that is why furring strips need to be used against masonry walls -- to create a dead air space for preventing moisture transfer.
Gypsum plaster is the modern material used today. Different types of aggregate may be specified by the builder such as clean river sand, perlite, pumice, or vermiculite. If fiber is required in a base coat, a special gypsum product is available which includes wood fibers. Lime putty, mixed with about 35 percent gypsum to help it harden may still be used as the finish coat.
Plaster of Paris
Plaster of Paris is a mixture of water and powdered gypsum that hardens without producing heat. It can be used to patch walls.
If you would like to mix your own plaster of Paris, here is the standard recipe:
10-lb. package of powdered gypsum
1 tsp. powdered alum
1-lb. package powdered wall sizing
Mix all dry ingredients together in a large metal tub and be sure all the ingredients are well mixed. You will have a lot of plaster mix here for future use and may want to store the remaining amount in 2-lb containers. Some people store the mix in 2-lb cloth baker’s bags. Store the bags in a cool, dry place out of reach of pets and children.
Mix the amount you need with just enough water to make a thick, creamy slurry that forms into mound easily. Use less water to make wall plaster and slightly more water if you want to use it for crafts and plaster casts.
And don’t forget to always use eye protection, masks and gloves when working with plaster, whether wet or dry. I just can’t stress this enough.
© Copyright www.diystuff.com
Top of Page
