Fog Coating Stucco

In this article, Mr. Geary makes it clear that most of the information he presents about color fog coating is available elsewhere, but that he intends to supplement this literature. He discusses reasons one would want to fog coat, and also why it is not necessary. He discusses the preparation of older versus new walls, as well as proper mixing procedures. He describes procedures for the application itself, clean up, and proper curing.





This article provides a detailed discussion of the subject of color fog coating for those in the construction industry who desire more specific information than is usually included in manufacturers' literature. It is intended that this paper should include most of the mixing and application information made available by stucco manufacturers and to supplement trade instructions which, of necessity, must be reasonably brief. This paper will be helpful to architects, designers and other professionals who desire detailed information about the product, reason for using it, preparation of the surface, mixing, application and curing.

Color fog coating is the process of lightly tinting the surface of newly-applied or aged stucco with cement paint of the same color as the stucco on the wall. The purpose of fogging is to achieve walls of uniform color, especially if it was required that stucco be applied while unfavorable conditions were in effect. For instance, an owner or builder may require application of the pigmented coat of stucco over portland cement plaster even though fog, rain, low temperature or other adverse drying condition has introduced a problem of non-uniformity of color. Factors other than weather conditions also may affect uniformity of color. Fog coating is not always standard procedure in the application of a color coat, especially if the pigmented coat of new plaster is applied during periods of favorable drying conditions.

Fog coating also is employed to overlay stains caused by dirt washed from roofs, discoloration due to soil clinging to and staining the base of walls and to cover non-removable efflorescence on the surface of newly-applied or aged plaster.

Fog coating can benefit any texture in stucco, whether it be sand float, Spanish, brocade, dash or other. Plasterers may fog coat concrete block walls with cement stucco paint also, in the same manner as is done to plaster, if the blocks are free of paint, waterproofing, sealing compound or other bond-preventing agent. Fog coat cement coating can be applied by brush or roller as well as by spray, if the texture of the substrate permits.

If a surface is over-coated by brushing a pigmented mixture onto the wall, the applied material normally would contain fine sand and would be called a brush coat.

The cement paint used for color fog coating is a finely ground powder produced by stucco manufacturers and is composed of cementitious materials, mineral pigments and sometimes other Ingredients which may beneficial to the ultimate quality of the tinting coat. Fog coating cement paint not contain sand as does stucco paint which is to be applied by fiber brush. The powder is mixed on the job site with clean water and sprayed evenly over the surface of the plastered walls to achieve uniform and attractive color. Cement paint for fog coating usually is packaged in containers smaller an those used for stucco. The tinting material must be stored m a thoroughly dry location, under the same controlled conditions established for storage of portland cement and manufactured stucco.

The following description of beneficial procedure relates to newly-applied plaster as well as to stucco that has been in service for a longer period of time and has stabilized. The procedure described here is proposed to enhance uniformity of color on walls as well as to obscure stabilized stains and non-removable efflorescence. Fog coating obscures problems related to variation in color, but cannot be expected to hide unsatisfactory finish techniques such as poor joining at scaffold decks or the juncture of two plasterers on one wan who use significantly different manipulation to texture stucco.


Normally, the only requirement for preparation of new walls is that windows and other areas requiring protection be masked. This protective requirement also applies to stucco of different color, or Marblecrete, if present on the same building. If new walls have a significant growth of loose, removable efflorescence, this deposit should be brushed from the stucco before the fog coat is applied. Mask or shield from overspray all areas of stucco that are not to be fog coated, as well as all other construction materials on the building. Special care should be taken to protect all aluminum trim or fixtures, and when finished, aluminum surfaces should be wiped clean.

Areas or materials which are not to be fog coated may be protected with a film of oil if the surfaces are non-absorbent or would not be stained by oil. Stucco and masonry, for instance, CANNOT be treated with oil, whereas metal surfaces may be.

New or old walls may be fogged when the substrate is dry or is SLIGHTLY BUT UNIFORMLY moist. Walls should not be wet at the time color fog coating is applied.

One expert in the field of color fog coating notes that most color fog coat projects done in Southern California are applied over dry substrate.


Walls that have been in service for some time require more preparation than the simple masking related to new plaster. Older walls must be cleaned prior to fogging, in order to promote good bond between the fog coat and substrate. The following cleaning instructions relate only to walls that have been in service sufficiently long that adequate bond cannot be achieved without cleaning. Soil, particulate matter from exhaust fumes and other aerial debris clinging to the substrate may act as a parting agent and prevent adequate bond.

A powerful stream of water from a jet nozzle attached to a water hose should be used to wash away all loose material in accordance with my article entitled "CLEANING AND CARE OF STUCCO WALLS". Cement plaster should be washed and allowed to partially dry prior to application of the color fog coat, to allow the plaster to attain uniformly low moisture content. The key word in the previous sentence is "uniformly". In geographical areas of low humidity and warm sun, I suggest at least a full day of drying time between power washing and application of the color fog coat to the wall. This time period should be extended during foggy or wet weather.


Before a fog coat project is started there should be on the job site sufficient fog coat powder of the needed coloration, a portable hand-pump sprayer (available under several brand names), an airless sprayer or a pressure tank-type sprayer. Sprayer hoses should be sufficiently long to allow efficient application by the operator. In addition, there should be a supply of used nylon stockings to be employed as a filtering medium to screen the coating into the sprayer, as well as several clean five gallon or larger plastic or rubber buckets or drums and a clean stirring stick.

The instructions of the stucco manufacturer concerning mixing, application and curing of the fog coat material must be studied and adhered to. To the extent that detailed procedure may not be provided by the manufacturer of the color fog coat material, you may be guided by this set of suggestions.

The size of the job will dictate whether five or fifty gallon mixing and storage containers will be employed. If large drums are used, it is advisable to line steel drums with large plastic bags to prevent contamination of color. Plastic trash barrels serve well and do not require lining with bags. Mix the cement paint in one plastic container and screen the mixed paint into the second plastic container or directly into the paint supply tank. For large scale production, the airless sprayer or pressure tank-type sprayer should have copper or heavy rubber tubing installed to keep the paint thoroughly mixed at all times.

To mix color fog coating for application to a wall, pour some dry tinting powder into a clean plastic or rubber container. Add clean water in small amounts to first produce a thick paste, stirring constantly. Only enough water should be added to the powder at first to develop a thick paste. Gradually add water while stirring constantly to thin the paste, breaking up any lumps which may have formed. Continue to add water and stir until all lumps have been eliminated and the fog coating mix reaches the consistency of thin paste.

The newly mixed fog coating blend then should be set aside to soak for about ten to fifteen minutes, so that water may be thoroughly absorbed into the particles of cement and lime.

After the ten to fifteen minutes soaking period, carefully add more water IF NEEDED, IN SMALL AMOUNTS, to avoid making the paste too thin. Add sufficient water to bring the fog coating paste to the consistency of milk, stirring constantly as water is added. Note that over-dilution of cement paint will result in inadequate coverage and hiding capability. The use of excessive mix water must be avoided when mixing all color coat material, whether stucco or color fog coat.

Mix slightly more color fog coat material than the estimated requirement for a given wall area. Save the excess mixed coating from the first wall until the second batch is mixed, then blend the remainder of the first batch into the second and mix thoroughly.

A section of nylon stocking should be placed over the opening to the supply tank of the spraying equipment. The milky mixture is to be poured through the nylon cloth filter into the tank.

An alternative to straining color fog coating mixture through a nylon stocking is to use a funnel with a suitably fine screen across the opening. After each use of the screened funnel, the screen and funnel must be reverse-flushed with water.

It is mandatory that the tinting paint be agitated in the sprayer tank regularly and frequently all the time that fog coating is being done. Cement, lime and pigment must not be allowed to settle onto the bottom of the tank because separation of ingredients will introduce variation in color. All ingredients must be kept in suspension.

In a tract of homes it is generally beneficial to plan that all houses of one color be fogged, then the sprayer supply tank cleaned and the next color of fog coat poured into the tank.


Note the following precaution. If a waterproofing agent has been applied previously to the lower portion of a stucco or concrete lock wall to prevent staining by fine clay clinging to the wall, it may be impossible for cement paint to bond to that protected surface. Bond or lack of bonding may depend upon the type of waterproofing agent employed.

Areas of waterproofed stucco or blocks should be tested to determine if the color fog coat application will adhere to the substrate.

A tinting fog coat should not be applied during periods of fog or rain. If applied during cold weather, the substrate must be dry.

The color fog coat should be sprayed onto the wall with a nozzle which forms a fan-shaped or circular spray pattern as the cement paint is sprayed from the hose. The nozzle of the sprayer should be held about eighteen inches from the wall. Sweep the nozzle around in a somewhat circular motion on the first pass over an area, then use a crosswise pattern on the second pass to be certain that all areas have been uniformly tinted. Normal procedure is to apply color fog coat from one architectural stoppage to another, such as corner to corner, or control joint to control joint. Usually a wall will not be spotted, although there are occasions and situations when spotting a small area can be done successfully. When spot fogging, there must be a good supply of air at the nozzle tip.

Two thin coats of color fog coat should be applied, allowing sufficient time between coats for the first application to dry. This delay may be as short as approximately fifteen minutes, if good drying conditions are in effect. Otherwise, longer drying time is required. Visual determination of readiness to receive the second application of color fog coat is sufficient. The second coating may be done when the first pass appears dry.

When using a portable sprayer, continue to agitate the sprayer and tinting paint regularly as the color fog coat is applied. In the case of large scale fogging operation, the supply tank of an airless sprayer or pressure tank-type sprayer should be provided with a small air line connected so that the tubing carries a reduced stream of air into the coating supply tank to keep the mixture thoroughly mixed at all times.

Tubing in base of paint supply tank to have tiny holes drilled at reasonable spacing, to allow air to exit tubing and agitate coating material.

Two applications of color fog coat have been found to be definitely superior to one application in order to accomplish the intended purpose. If only one coat of fog coat is applied, the variation which was intended to be obscured may show through the single layer when the wall is wet by rain.

Mixed color fog coat material should be applied within two hours after first contact with water or the batch should be wasted and a new batch mixed.

It is advisable to allow applied stucco to dry or at least attain a reasonably low level of moisture content which is uniform over the entire surface of the stucco wall, prior to tinting. There should not be patches of moist and dry substrate on the same wall. The principal criterion to accomplish a successful color fog coating application is uniformity of moisture content within the substrate over all of the wall surface.

Note that color fog coat will not hide migrating stain such as creosote or oil applied by vandals.

In routine fogging of houses and apartment buildings, cement paint should be applied to the plaster before the window cleaners start their operation.

A typical plasterer will fog about ten to fifteen tract houses in a day, and sometimes more, or an equivalent area of apartment buildings. When fog coating two-story buildings, extension wands sometimes are employed to accomplish spraying from the ground. These wands may be as much as eighteen feet in length.


After completion of the tinting operation or prior to any extended delay, the hose and nozzle of spray equipment should be washed so that cement cannot set up inside the passageway and cause future problems.

Use clean water and a clean brush or rag to remove objectionable over-spray within a reasonable period of time, before the cement paste has bonded.

Clean the storage tank, sprayer, hose and nozzle thoroughly after color fog coating has been completed.


A fog coat becomes an integral part of a clean and receptive base when applied properly and cured well. Natural curing can take place when the air becomes damp or foggy following application of the coating.

It is permissable, and in hot or dry weather advisable, to moist cure the coating. This is accomplished by application of a fine, misty spray of clean water, under low pressure, from a special fog spray nozzle on a hose, ON THE DAY FOLLOWING APPLICATION OF THE COLOR FOG COAT.

Do not direct a heavy stream of water against a new color fog coat until the coating has had sufficient time and favorable curing conditions to attain strength, bond and toughness. Do not dampen new coating when the wall is hot from intense sunlight. Complete curing requires a period of at least several weeks with some exposure to moisture to hydrate the cement portion of the fog coat. Initially, one may expect to observe some chalkiness on the surface, which will disappear as moisture hydrates the cement.

To develop a really hard fog coat one may add a gallon of good modifying agent such as acrylic resin to the approximately twenty five pounds of dry fog coat powder and approximately eight to ten gallons of mix water in each batch.



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