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Why is stucco susceptible to mold?

Whenever moisture, air and a food source are present, mold can grow.
If a home is constructed with masonry or artificial stucco (EIFS), special attention must be paid to any openings such as windows and doors and how roof and wall lines are terminated. There are many ways water can penetrate into stucco, and any wall penetrations and flashings are suspect. Improperly installed windows and doors, insufficient or improper caulking work, and especially improper flashing terminations, are all known to allow water penetration.
At roof lines that terminate at wall lines, “kick out” flashing is imperative whether it is hard coat or artificial stucco. Applicable IRC codes are:

R703.8 Flashing. Approved corrosion-resistant flashing shall be applied shingle-fashion in such a manner to prevent entry of water into the wall cavity or penetration of water to the building structural framing components. The flashing shall extend to the surface of the exterior wall finish. Approved corrosion-resistant flashings shall be installed at all of the following locations:

1. Exterior window and door openings. Flashing at exterior window and door openings shall extend to the surface of the exterior wall finish or to the water-resistive barrier for subsequent drainage.

2. At the intersection of chimneys or other masonry construction with frame or stucco walls, with projecting lips on both sides under stucco copings.

3. Under and at the ends of masonry, wood or metal copings and sills.

4. Continuously above all projecting wood trim.

5. Where exterior porches, decks or stairs attach to a wall or floor assembly of wood-frame construction.

6. At wall and roof intersections.

7. At built-in gutters.

R703.9 Exterior insulation finish systems, general.
All exterior Insulation Finish Systems (EIFS) shall be installed in accordance with the manufacturer’s installation instructions and the requirements of this section. Decorative trim shall not be face nailed through the EIFS. The EIFS shall terminate not less than 6 inches (152 mm) above the finished ground level.

R703.9.1 Water-resistive barrier.
All EIFS shall have water-resistive barrier applied between the underlying water-sensitive building components and the exterior insulation, and a means of draining water to the exterior of the veneer. A water-resistive barrier shall be compliant with ASTM D226Type I asphalt saturated felt or equivalent, shall be applied horizontally with the upper layer lapped over the
lower layer not less than 2 inches (51 mm), and shall have all vertical joints lapped not less than 6 inches (152 mm).

R703.9.2 Flashing, general.
Flashing of EIFS shall be provided in accordance with the requirements of Section R703.8. It is bad flashing jobs and poorly installed windows and doors allow rainwater to run down the roof or wall and end up inside where it shouldn’t be. Mold loves dark, moist spaces like the inside of your walls where it can flourish. There it can eat building materials have moisture and grow.

EIFS (exterior insulation finishing system) sometimes called artificial stucco, is made with a chemical compound, foam sheets and an acrylic finish. The problem with the material is that it traps and repels water equally well. If water seeps into the wall covering during or after construction, it's difficult to get out, creating a prime feeding ground for mold. The underlayment for stucco, which is usually oriented strand board (OSB) absorbs moisture easily. Note that the best underlayment for stucco is treated plywood, which is much better than OSB for this purpose. Moisture can “travel” and often moves inward from the source - it moves towards least resistance. Therefore, moisture coming in from a poorly flashed window can be found elsewhere in the house having traveled, under the flooring for instance. Fernando, of Preferred Home Inspections, Inc., uses both invasive and non-invasive state-of-the- art moisture detectors to track moisture down at the source: two Delmhorst BD2100s, one with stucco prods and a David White Tramex Moisture Encounter. With these two distinctively different meters, all types of surfaces can be checked for excessive moisture.

Hard coat or “real” stucco, siding and brick cladding can have moisture problems, too. Did you know that a masonry stucco home could also have EIFS banding around the most critical places – doors, windows and roof lines? With brick, leaking occurs from the same problems as EIFS: improperly installed windows, doors, fireplace chimney and roof flashings. Water can also rise from the ground and penetrate inside, something Fernando has termed “self-flooding”. This normally occurs when a homeowner does not have a 6” drop in 10’ away from the house, for instance, with high mulch beds. Brick cladding has an air gap between the interior wall and the brick with “weepholes” that allows moisture to leave the building (IF it was built properly) and hard coat stucco should have a “weep screed” - flashing at the bottom, ideally to let moisture have an escape route. All modern homes should also have a moisture barrier to complete the envelope. IRC code which applies is: R703.6.2.1:

R703.6.2.1 Weep screeds.
A minimum 0.019-inch (0.5mm) (No. 26 galvanized sheet gage), corrosion-resistant weep screed or plastic weep screed, with a minimum vertical attachment flange of 31/2 inches (89 mm) shall be provided at or below the foundation plate line on exterior stud walls in accordance with ASTM C 926. The weep screed shall be placed a minimum of 4 inches (102 mm)
above the earth or 2 inches (51 mm) above paved areas and shall be of a type that will allow trapped water to drain to the exterior of the building. The weather-resistant barrier shall lap the attachment flange. The exterior lath shall cover and terminate on the attachment flange of the weep screed.

How is stucco inspected?
Fernando has intimate knowledge of how both kinds of stucco should be installed because he is both certified and has personally installed both types in homebuilding and remodeling ventures. To have this basic understanding of how masonry and EIFS stucco should properly be installed is the basis for knowing how to inspect it.

State-of-the-art equipment.
Fernando has extensive experience inspecting stucco homes. He first performs a visual inspection on the exterior. Using three moisture meters, two Delmhorst BD2100s, one with Stucco prod, and a David White Tramex Moisture Encounter he will check both interior and exterior locations for probable water penetration and extent of damage.

He will record the horizontal plane of the slab or upper floors using a digital water level.
Photo documentation accompanies the extensive report he issues after the inspection.
Recommend mold or indoor air quality testing, if needed, and perform the tests on-site

When testing is completed, collection samples are immediately over-nighted to a lab in Florida for next day results (or same-day, if requested).
If the test results are positive for elevated mold, consultation with homeowner/buyer will follow. An assessment, evaluation and explanation of the lab report are issued.
If the test results are negative for elevated mold, a report is issued with the results to keep with the home’s records.

Note that additional site visits may be needed - consultation and re-testing may be necessary to isolate the exact areas and types of mold found.
Protocol for remediation for repair of the mold situation can be provided for extra fee.
If supervisory inspections during the removal process is desired/needed, Fernando can supply this type of inspection also.

Please feel free to call us with any questions and for cost of each type of inspection:

Masonry stucco and moisture
EIFS (entirely) Inspection