Stucco Colors, Notes and Suggestions
From Erin Allen of
Earth Pigments Company.
We would like to thank Erin Allen for these comments. Erin is one of the nation’s leading stucco color and pigment specialists. For more information about her or her company please visit earthpigments.com
Many stucco colors come from Natural pigments. This can be a very diverse range of colors such as Dan Brady found in an Indian Market at a stall selling pigments.
The idea of tinting stucco with color for homes and public buildings is not new. It goes far back to Roman times when local Ochers were utilized to create beautiful, integral shades in exterior lime coatings. Any type of stucco can be colored, whether it is a pure lime plaster or contemporary cement stucco. Colorants used for exteriors are pigments, in particular inorganic pigments of mineral origin. Only these colors are compatible with the high ph of cement products, and possess the lightfastness required. Inorganic pigments will be either natural such as Ochers and natural earths or man made colors such as manufactured Iron Oxides. These two types, natural and man made, both have advantages and disadvantages in their use.
Figure 2 Stucco can also be purchased precolored by the factory. A stucco color chart gives a representation of the final product.
Using Natural Ochers and Pigments For Stucco Colors
Natural Ochers and Earths have traditionally been used in both their pure form and as a more rudimentary clay. If one wishes to achieve the most natural shade possible, or one that is historically accurate before the advent of manufactured pigments, then nothing can replace these natural shades. By their very nature they can produce a light refraction much more pleasing to the eye than flat manufactured colors.
Being natural, they also possess one other attribute that no man made colorant can achieve–permanence to UV. They have a disadvantage in that they do not possess as much tinting strength as manufactured colors.
Using Manufactured Stucco Colors
Man-made stucco colorants have come a long way in recent years and their use has far exceeded that of natural earths and Ochers. Manufacturers have been able to concentrate the color so that darker shades can be achieved. Although these colors are a manufactured byproduct of minerals such as iron, they are often referred to as “natural.” Manufactured colors offer a wider range of shades, such as blues and dark greens that do not occur in natural soils. They also come in a wide variety of earth tones ranging from yellows to reds and many brown and gray tones. Because they are inorganic mineral based pigments they possess excellent UV stability for the life of the coating. They are similar in tone to many natural pigments, but man-made color cannot completely duplicate those of Mother Nature. Stucco colors can also be created using liquid iron oxides manufactured for use with cement. Follow label instructions when using these products. When choosing stucco colors for houses, think long term. Look at the surroundings and choose the tones that you will be happy with for a very long time.
There are other ways to look at stucco color, both natural and manufactured. Stucco color can also be grouped by types of tones:
- Earth tones such as beiges and browns
- Sun tones of yellows, oranges and reds
- Water tones of cool blues and greens
Often ones region will determine color preference. Sometimes it is a cultural influence and other times it stems from local availability and/or tradition.
Figure 3 Pigment powders are represented on this chart of natural and manufactured colors.
Determining Pigment Rations and Mixing Procedures
There are a few determining factors used to calculate dry pigment ratios in stucco. Ratios are always based on the dry weight of the binder(s) used.
- Whether the stucco is cement or pure lime
- In the case of lime, which pigment is chosen
- How light a tint is desired
Calculating Pigment Ratio in Cement Based Stuccos
To add integral color to your cement stucco mix, calculate your proportion by the weight of the dry cement before the addition of water and aggregate. If lime is used its weight is also included in the calculation. The ratio cannot exceed 10%. Pigment color is added directly into the concrete mixer, without any additional water. The use of an additional concrete bonding agent is recommended. Controls at a job site must be in place to ensure that color is added in the correct weight ratio, mixed properly, that ingredients are not contaminated and remain consistent.
Mechanical mixing is recommended following these directions:
Briefly mix together the listed amounts in this order
- 75% of the water
- 50% of the sand
- 100% Pigment ratio
- 100% Cement (and lime if applicable)
- 100% of any additional bonding agent, if used
Then add the remainder of the water and sand and mix to a workable consistency. Once the proper consistency has been reached, the batch must then be mixed for an additional full 5 minutes. Mix only the amount of mortar to be worked immediately. If additional water is added to mortar that has become stiff, the color will be affected.
Calculating Pigment Ratios in Pure Lime Coatings
Lime coatings are unique from cement-based stuccos in how color can be achieved. They can hold a higher proportion of pigment to the binder. Pure lime offers a unique light refraction when combined with pigments and Ochers. And for deepening of color, lime coatings allow techniques that take advantage of the carbonation process such as fresco coloring and patina coats.
To obtain colored lime plaster, Ochers and pigments can be added in ratio to the dry weight of lime to be employed, before the addition of any aggregate. Mixing instructions for lime would follow the same order as those for cement stucco. The amount of pigment used will depend upon the depth of tint desired, and whether the pigment is a natural earth or a manufactured Oxide. This amount used should not exceed the upper end of these ratios:
- Ochers and Natural Pigments 3% to 20% of the weight of the dry lime
- Manufactured Oxide Pigments 3% to 15% of the weight of the dry lime
If using lime putty rather than hydrated lime powder, calculate that approximately 1/3 of that putty’s volume is water. Therefore safely calculate the weight of water in one gallon of lime putty to be around 3 lbs, and the remaining weight to be lime. It is this remaining weight that you will base your calculation on. If using a readymade bagged dry lime plaster that already contains aggregate, calculate 25% of the weight of that mix as your lime binder. That will be the weight you calculate your amount of Ocher or pigment to.
The Importance of Creating Samples
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, and
- 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.
Efflorescence in Colored Concrete and Stucco
Efflorescence or “bloom” is a type of white stain that can appear on the surface of concrete, lime and other masonry surfaces. It results when water passes through the concrete, bringing water-soluble salts and other materials in the substrate with it to the surface.
The addition of pigment does not have any bearing on whether or not efflorescence will occur, but it is certainly more obvious on a colored surface. It can be caused by extra water added during toweling, exposure to lower temperatures, rain, excess humidity, etc. and exhibits no time preference to make its appearance. Luckily efflorescence is one of the easier stains to clean, especially if new. Dry brushing with water and a stiff brush can often remove light stains. Heavier, well-established efflorescence from salts is generally removed by using muriatic acid in a solution:
- 1 part muriatic acid
- 12 parts of water
Wet the surface thoroughly before and after scrubbing the solution. Muriatic acid is very dangerous to work with, therefore proper precautions must be taken and label directions must be followed. Stains that are not removed by this method may require proprietary compounds to remove.
Stucco color notes from Herb Nordmeyer:
For interior work, the liquid paint pigments for latex paints work well. They disburse very readily. I’ve used some of the pigments for exterior work successfully, but getting away from the earth they sometimes fade.
One grain of pigment has as much tinting power as a clump of 10 grains of pigment, so to get the full benefit of the pigment you need to get it disbursed. To do this, add the pigment to the mixer after 75% of the water and half of the sand have been added. Mix each batch for exactly the same time.
Natural Ochers are often used as stucco colorant (below) Photo Credit JM Steber
Stay away from carbon black.
It gives a beautiful black color, but as a wall heats up and cools from the sun, the particles close to the surface slip out of the stucco and the color fades (think graphite). One McDonald’s restaurant I examined had jet black pigment on the north side and under the eaves, but wherever the sun struck the west side, it looked like normal gray pigment.
Using Natural pigments in stucco instead of paint can lower the VOCs off gassing from a structure. This can be an important feature especially in interior plaster. To check the color of the finished product, dry mix the pigment and stucco (with or without sand) and then flatten it out with a piece of glass (I use lens covers from welding hoods). The stucco color will not be exact, but very close.