Concrete plaster is most commonly used in the creation of outdoor concrete lawn ornaments and sculptures. This medium is a favorite for "free-form" sculptures that are made without molds. The concrete plaster is usually applied to a wire mesh base structure known as an armature. When produced correctly, the resulting structure can endure for many years, even in harsh outdoor weather.
Things You'll Need
Sturdy waterproof gloves
Two 5-gallon buckets
6 to 8 cups of Portland cement
Masonry sand (optional)
1/4 cup polypropylene reinforcing fibers 1/2 to 3/4 inch long
1 cup acrylic or latex admixture liquid bonding additive
1 cup latex house paint (any color)
2 cups water
Drywall power mixing drill and spiral mixer
Put on waterproof gloves and wear them throughout the process. Pour 6 cups of Portland cement into one of the 5-gallon buckets. If you desire a stronger, more waterproof mixture, use up to 3 cups of masonry sand in place of 3 cups of Portland cement. If you mix in sand, blend the two thoroughly with a long-handled spoon or mixing drill at a medium setting.
Add polypropylene fibers a pinch at a time to a measuring cup, separating them so they are loose rather than packed down. These fibers go a long way, so do not use more than the recommended 1/4 cup.
Add the polypropylene fibers to the dry mixture and blend well.
Mix 1 cup of admixture, 1 cup of paint, and 1 cup of water in the second 5-gallon bucket. Blend it together thoroughly.
Add the liquid mixture to the bucket containing the dry mix. Blend all the ingredients until it resembles thickened peanut butter. If it is too runny, add up to 2 additional cups of Portland cement in small amounts at a time, but do not exceed the recommended 8 cups of total dry mixture. Blend often and well, testing the consistency with each addition of cement. When it is done, a large spoonful of the mixture should maintain its shape when dropped onto the rest of the batch.
Use the concrete plaster immediately. You will only have about 30 minutes before the mixture begins to set and becomes too rigid to work with easily.
A heavy-duty, long-handled mixing spoon can be used for combining ingredients if you do not have a drywall power mixing drill and spiral mixer.
If you are planning to use the concrete plaster with a wire armature, it will need to have a consistency of clay rather than thick peanut butter to it maintains its shape while the final piece is curing.
Concrete plaster may cause injury to your skin, so always wear durable waterproof gloves when handling it.
Although a little water can be added to a stiffening mixture one time only to improve pliability, repeating the addition of water will cause the strength of the final sculpture to be compromised.