CRAZE CRACKING IN STUCCO
Craze cracking occurs, sometimes, in a coat of stucco, which is the third or color coat of plaster applied to a building over the two base coats of cement plaster. Craze cracking in a coat of stucco has essentially the same appearance as craze cracking in old china ware. In china ware, craze cracking normally is observed in older plates, cups and saucers, but there will typically be no observable opening in the dishes. They merely are fine lines on the surface of dishes, which develop during exposure of the vessels to alternate hot water and cooling.
Craze cracks in stucco are short, extremely fine and tight fissures in the surface of the color coat (the coat of stucco) which has been applied over a brown coat of portland cement plaster. Craze cracks are always short, typically about one-eighth inch (1/8") to about one-half inch ('5") long. Oftentimes they are evident only as short, fine lines on the surface of stucco, rather than as openings or fissures. The fissures exist only in the third or color coat, and not in the base coats of cement plaster behind the stucco. The myriad fine, tight fissures do not detract from the integrity of the finish coat of stucco, nor from the base coats of portland cement plaster. The problem, if one exists, is esthetic in nature. Normally, craze cracking is evident only when viewed closely. It is not readily apparent when one is positioned further from the wall.
It is my opinion that craze cracks in stucco sometimes may be related to the richness of the formulation, because stucco contains a higher percentage of portland cement and hydrated lime than base coat cement plaster in the scratch and brown coats. Sometimes craze cracking may be related to an excessive amount of mix water, or to a rapid drying of the surface, under adverse drying conditions.
Craze cracking, per se, is not harmful to the finished wall, and is not an indication of deterioration or degradation. It is only a surface phenomenon. No remedial work is required, normally. If craze cracking is pervasive and readily evident, remediation may be considered.
If it is desired that micro cracks be obscured, several possible methods may be considered, although coverage is unnecessary.
Sometimes application of a color fog coat of stucco material, of the same color as originally applied, will obscure the micro cracks. To determine the feasibility of a color fog coat as a method of remediation, I suggest that a small amount of fog coat powder be mixed with water, sprayed onto a square yard or two of the wall, and allowed to cure and dry. After the fog coat has cured and dried, the effectiveness of that application can be evaluated.
If a color fog coat does not cover the micro cracks in a satisfactory manner, a brush coat of cementitious stucco paint, composed of the same stucco powder originally applied to the wall, may be brushed over the surface of the wall, and, later, gently moist cured. The stucco paint generally is laid on with a heavy fiber brush over all of the wall surface, as needed.
A third method is application of another coat of stucco, over the original, if the owner wishes to expend the extra funds. One of the first two methods should resolve the matter to the satisfaction of all concerned.
I reiterate that covering craze cracks in a coat of stucco is not necessary for protection of the wall.