Jenny Lee
Plaster Molding
General Information
Plaster molding creates products with a smooth surface finish which allows for the casting of intricate shapes. It is a mixture of gypsum, strengthening compounds, and water. Additives such as talc or magnesium oxide are used to improve strength, permeability, and castability.
The design begins with a CAD file or drawing that is created into a pattern through stereolithography, traditional handcrafting, or with a machine. Negative molds are made from the model which in turn makes a positive resin cope and drag pattern. Liquid plaster slurry is then poured around the cope and drag pattern and into core boxes. The plaster mold is then removed and baked to get rid of any moisture.
This process is more expensive because it is highly-skilled, labor-intensive work. Plaster is somewhat soluble in water and sensitive to acids. Therefore, cleaning must be done gently with a soft cloth and with minimal water exposure.
Environmental Impact
Plaster molding is a sustainable design element thanks to its composition of natural materials. The energy used for extraction and production is minimal. It is also often sourced locally and relies on skilled manual labor rather than mechanical equipment. Plaster products can also be recycled or reused to avoid any waste.
After it is installed, there is no problem with indoor air quality. Plaster does not give off any VOCs when it remains undisturbed.
Use in Interior Setting
1. These plaster sculptures showcase a mottled surface made from a running mold process where a metal profile is run through wet plaster.
2. Plaster molding is used as a decorative ceiling treatment for an elegant finish.
3. This functional wall features heated plaster forms on a plaster wall surface that can be used to manipulate trigger points on parts of the body such as the shoulders, neck, and knees.
4. Geometric and linear forms are created using plaster molding to give off a contemporary feel.
5. This home theatre features ornate details using different types of plaster molding.
Crown Molding
A plaster crown molding eases the transition from ceiling to wall and also adds a detail of elegance to a space. For this application, it is important to prime and paint the crown molding to prevent warping. After this step, cut the crown molding to size using the appropriate joints (mitered or coped). Afterward, it is typically painted with a semi-gloss or high-gloss finish. High-gloss paints are durable and shiny but can appear worn down over time.
Testing Organizations:
National Plasterers Council - https://www.npconline.org/
PCA - https://www.cement.org/learn/materials-applications/stucco/stucco-installation-standards
Relevant standards through ASTM:
C59 - Specification for Gypsum Casting Plaster and Gypsum Molding Plaster
C28 - Specification for Gypsum Plasters
Sources
1. Knowles, E. & Miller, K. (2014) "A Comprehensive Guide for Selecting Interior Finishes."
2. https://www.armstrongrm.com/pages/plastermold2-tech.html
3. https://www.thomasnet.com/articles/custom-manufacturing-fabricating/all-about-plaster-mold-casting/
5. https://www.decocraftusa.com/add-sustainable-design-plaster-moulding/