While in the store recently with my work shirt with my business name on, the cashier asked me if I did stucco.  I answered yes and the cashier told me that one of their customers indicated that their house was condemned because black mold in it was making them sick.  I have heard of black mold in builders’ literature, but have never seen it blamed on stucco.  It seems that if anything goes wrong with a house, they blame it on stucco.  I know that stucco has been around as long as brick, but no one seems to say anything about brick.  What do you think?- Renee, Louisiana 

            As you indicate, stucco has a long history of use.  In many parts of Europe it is the primary exterior finish.  In many European countries, it is applied directly over relatively-dense cement blocks.

            Stucco as an exterior finishing or siding material is more commonly used in southern states (very common in Florida) than it is in the north.  It is also used on Tudor-style houses in some parts of the U.S.

            Stucco is a plaster-type material with a cement base.  A variety of cements are used in the stucco mixture depending on climate and the texture desired.  It is usually applied over a base of wire mesh, wooden slot spacers, building paper and plywood or oriented-strand board sheathing (OSB).

            Stucco surfacing materials are typically applied in three layers by hand troweling or by spraying.  Some products are applied as a single layer.

            In addition to these more traditional stucco exterior surfacing materials, “synthetic” stucco (EIFS) products are being widely promoted and applied in southeastern states.  These materials are the subject of a major class action lawsuit because of alleged moisture penetration into wall materials and subsequent mold infestation.

            Stucco is a relatively porous material.  As such, rainwater can move from the exterior surface where it can come into contact with wood spacers and in the worst case with plywood or OSB wall sheathing.  Several years ago a stucco-clad Tudor-style restaurant building underwent renovation in our area.  Where the stucco had been, the OSB was blackened (apparently by mold).

            Because of its porosity, stucco needs to be applied to concrete or fibrocement panels to keep water from coming into contact with wood-based wall materials.  In many typical applications, water that penetrates stucco must have a way of out of the wall.  As such, water should be able to trickle down to the base and come out through weep holes.  Alternatively the space between the stucco and interior surface and wood sheathing needs to allow for air movement.

            Stucco is subject to settling cracks as well.  These settling cracks pose a risk of water intrusion into the wall and mold infestation.  Of particular concern are exterior walls subject to wind-driven rains.  Houses out in the open are quite vulnerable to rainwater penetration of porous exterior cladding.

            You asked “how about brick”.  Though brick veneer is not as porous as stucco, many brick homes do in fact experience similar water penetration problems.