CONTROL OF COLOR IN STUCCO
Variation in color of applied stucco is rare, but, because it does occur occasionally, a discussion of preventative measures is appropriate. In the few cases where differences in color have occurred, one or more of the following reasons may have caused the problem.
Adverse weather conditions
Transportation of wet-mixed stucco
Subsequent exposure to unusual or improper situations or conditions
Color variation may be apparent as actual difference in coloration, blotchiness, or because of a deposit of efflorescence. Occasionally, a few persons have been confused by variation in texture, with resultant difference of light reflectance from the surface; thinking that they were seeing variation in color. A discussion about some of the factors which might relate to variation in color on a wall or soffit will follow this introduction.
1. Adverse weather conditions at the time of application, such as low air temperature; or overcast, fog or rain may induce blotchiness in the third or color coat.
2. Lack of uniformity of suction in the brown coat prior to application of the coat of stucco. Non-uniformity of suction may be a result of one or more of the following factors or conditions affecting the brown coat.
- Variation in thickness of the base coats.
- Over-spray of extraneous materials such as paint or a waterproofing agent, by other trades.
- Rough or "Open" surface at joinings of adjacent areas of brown coat on a wall, such as at cold joints.
- Excessively smooth floating of the brown coat in some areas, while other areas of brown coat are open and more absorbent.
- Spotty freezing, or serious retardation of hydration of cement in the brown coat, in some areas but not in others.
- Uneven pre-wetting of the brown coat, prior to application of the color coat.
Dry-rodding or dry-raking of the brown coat, after it has firmed slightly, is beneficial, but is not normally done on "economy type" construction. That action is observed on commercial work or custom homes.
3. Failure to maintain mix proportions of aggregate to cement, if color coat material is proportioned on the job site, rather than being manufactured in a stucco plant.
4. Unequal amounts of mix water in different batches of color coat material.
5. Unequal proportions of lime, pigment, or other approved admixture, in successive batches, if formulated on-site.
6. Separation of pigment during transportation of mixed wet stucco from the mixer to a mortar board, if batches of stucco have been mixed too wet or fluid. This may happen in the wheelbarrow due to vibration during travel of the barrow over rough ground, on the job site.
7. A portion of a wall screened from normal uniformly fast drying of the color coat by a shade tree or adjacent building.
8. Insufficient mixing time of job-proportioned stucco coat, on the job site.
9. Inadequate coverage of the brown coat by sufficient thickness of stucco. That problem is more commonly observed in cases where only a single pass, application of stucco is done.
10. Spreading the coat of stucco too thinly.
11. Sponge type floats becoming loaded, or filled, with fine material from batches of stucco, such as cement, lime and pigment.
12. Contamination due to dirty equipment, mix water, or tools.
13. Rain impinging against relatively fresh color coat, or washing by activity of landscaping people.
14. Improperly installed rain gutters or downspouts, or leaks in the same.
15. Moist-curing fresh pigmented stucco improperly.
16. Lack of control of cleaning water as it is used to remove unwanted wet material from other surfaces.
17. Cold joints in colored stucco.
18. Use of excessive floating water at joinings.
19. Uneven drying of the coat of stucco. All areas of colored stucco should dry at a uniform rate, to avoid discoloration.
20. Exudation of efflorescence upon the finished surface.
21. Spattering of fine particles of soil upon the base of the wall during periods of rain, or when watering adjacent plants.
22. Growth of mold or mildew on the surface, which may impart a black, dark green, or light green color to the surface.
23. Rust from iron or steel fixtures or attachments, or stain from copper roofing or fixtures.
24. Wood sap or resin being deposited upon the surface, especially at tops of railings, parapet walls, wing walls, plastered fences, etc. That ill-effect is more prevalent under some trees than other types of growth.
25. Blowing dust, dirt and other aerial debris, such as petroleum particulates becoming lodged in a resinous coating on plaster, below some kinds of tree;
26. Uneven hydration of the cement paste due to shadow lines established by scaffolding and planks remaining in place too long after completion of walls.
In the event that variation in color has occurred, for one or more of various possible reasons, suitable correction oftentimes can be affected by fog coating. For details of that process, please refer to my article entitled "FOG COATING STUCCO".