To obtain colored Clay plaster, Ochers and pigments can be added in ratio to the dry weight of the Clay binder in the mix. The amount used will depend upon the depth of tint desired and whether the pigment is a natural one or a manufactured one. To determine how much pigment to add, choose a pigment from one our of our Categories and follow these guidelines:
- Natural Earth and Ocher Pigments: Up to 10% of the weight of the dry plaster
- French Mineral Pigments: up to 10% of the weight of the dry plaster
- Oxide Pigments: Up to 5% of the weight of the dry plaster
These are maximum ratios. Beautiful light tones can be achieved with as little as 3% to the weight of the dry plaster. If using a readymade product that is already colored, ratios up to 3% can be added to "pull" colors in a different direction.
It cannot be stressed enough the need to do sample testing for your colors. It is important to:
- Establish proper ratios
- Determine the final color when actually dry
- See the sample in different light
For batch to batch consistency, ratios should always be determined by weight rather than volume as pigment is like flour and the weight of any volume measurement can differ. It is also important to make sure that a sample has completely dried to see the truest color. After adequate drying time, test for any moisture in the sample by holding your hand or cheek against it. Moisture will feel cool to the touch. If a small sample board is created, move it around to different locations to see how the color looks in different light. It may look different in one room from another. Part of the beauty of pigment in clay plaster is how it changes with the changing light.
To mix, slake the pigment in an equal volume of water and work to create a homogenous paste. It is important that all the pigment particles be wetted to prevent dry particles that could result in "microbursting" during application. This is the appearance of specks of unslaked pigment that can streak. Sometimes minimal microbursting will occur but can be worked out with the trowel. Add the slaked paste to the wet plaster mix. The use of a mixing paddle attachment is recommended. Follow the proper application instructions for your product and type of mix.