How Pressure Cleaning Prevents Mold and Mildew After a Storm

We examine the importance of pressure cleaning in mold and mildew prevention after storm events or facilities water damage.

We look at why post-storm conditions are perfect for fungal growth, the science of pressure washing, where to apply it, when to apply it and the long term benefits. Practical insights will be provided to facility managers and property owners on how to implement preventative maintenance programs that safeguard building integrity, occupant health and financial investments.

The Hidden Threat After Storm Season

Storms pass through, leaving more than visible debris and water damage in their wake. The perfect conditions for a more insidious threat: mold and mildew infiltration, are created in the aftermath. While fallen trees and structural damage must be addressed quickly, it’s the unseen moisture trapped in building materials and organic debris that can continue to threaten commercial properties.

Fungal proliferation is favored in several ways in post storm environments. During rainfall or flooding events, first building materials absorb moisture. Second, humidity levels stay high for days after storms. Third, organic debris such as leaves, soil and plant matter build up against building surfaces, creating moisture trapping pockets where fungi live.

The speed at which mold sets up colonies is what makes this so concerning. Industry standard states that mold can start to grow on suitable surfaces in as little as 24-48 hours after moisture exposure. With this fast development timeline, property managers have little time to act before remediation becomes much more complicated and expensive.

It is a big deal financially. According to the Institute of Inspection, Cleaning and Restoration Certification (IICRC), professional mold remediation can cost $15-$30 per square foot which is far more than preventative maintenance. In addition to financial issues, mold is known to be a health hazard to building occupants, especially those with respiratory problems, allergies or compromised immune systems.

The development cycle of mold colonies is interrupted by immediate action through properly executed pressure cleaning before the colonies are able to establish themselves in building materials. Instead of just treating surface appearance, strategic pressure washing after storms is an important first line of defense against both structural deterioration and indoor air quality issues.

Understanding Post-Storm Moisture Problems

There are predictable patterns to the relationship between storm events and subsequent mold growth which facility managers must be aware of in order to implement effective countermeasures. Excessive moisture is able to penetrate commercial buildings and exterior surfaces through multiple pathways created by storms.

Direct water infiltration is the first type of infiltration that occurs through compromised building envelopes (damaged roofing, cracked sealants or failed flashing) that allow rainwater to penetrate normally protected surfaces.

Second, standing water is drawn into porous building materials such as concrete, brick and wood by capillary action.

Third, it increases atmospheric humidity that extends drying times for all surfaces to within the range of deal moisture levels for fungal development (generally above 60% relative humidity).

Some areas are always more vulnerable to post storm mold growth:

• Exterior wall systems: Especially at transitions between materials and around penetrations
• Roof assemblies: Particularly flat or low-slope commercial roofing where drainage may be compromised
• Foundation perimeters: Where splash-back from downpours saturates lower wall sections
• Decks and outdoor amenity spaces: Especially wooden structures with limited ventilation underneath
• Gutters and drainage components: Where organic debris accumulates and traps moisture
• Porous hardscapes: Including concrete walkways, driveways, and parking areas

Mold spores which are ubiquitous in outdoor environments, begin germination within 24 hours of moisture exposure to suitable surfaces. In 48 hours, highly susceptible materials may already begin to form visible colonies. Mold normally establishes sufficient biomass to release additional spores after 72 hours which speeds spread to adjacent areas.

Because of this compressed timeline, established mold colonies can develop over the weekend before maintenance staff can return on Monday. Because of this rapid development cycle, facility managers must develop response protocols for this rapid development cycle, especially during warm seasons when temperatures further accelerate growth rates.

The Science Behind Pressure Cleaning Prevention

The mechanisms by which pressure cleaning disrupts the mold growth cycle are multiple and work synergistically to create hostile environments to fungal establishment. The understanding of these scientific principles enables maintenance teams to optimize their approach to be the most effective.

Pressure washing is at its core a combination of mechanical force and chemical treatments to accomplish three critical things:

1. Physical removal of spores and existing growth: The high pressure water stream (commercial applications typically 1500 – 3000 PSI) physically dislodges mold spores, hyphal fragments and early stage colonies from surfaces. The mechanical action removes the visible growth and the microscopic reproductive structures that will spread contamination.
2. Elimination of nutrient sources: Mold needs organic material to feed on so we can eliminate the sources of nutrients. Pressure washing removes accumulated organic debris such as pollen, dirt, leaf fragments, insect waste, that would otherwise nourish fungal growth. It also makes the environment hostile even if some spores remain.
3. Delivery of antimicrobial agents: Pressure washing is more than a cleaning method when combined with appropriate biocides and becomes a method of delivery of antimicrobial agents. Antimicrobial solutions are forced into microscopic surface irregularities that cannot be reached by manual cleaning.

The most effective pressure washing protocols for mold prevention use EPA registered antimicrobial solutions containing quaternary ammonium compounds or sodium hypochlorite (bleach) at appropriate dilutions.

These chemicals break cell membranes and metabolic functions of fungal organisms. Most importantly, pressure washing force helps these agents to penetrate biofilms, protective layers that developing mold colonies create which makes them much more effective than just spraying solutions on surfaces.

Optimization also depends on temperature. Both cleaning efficacy and antimicrobial activity are enhanced by hot water pressure washing (140-200°F). Heat destabilizes microbial cell structures and it increases the reactivity of cleaning chemicals. Yet, operators must weigh the benefits of temperature against the possibility of damaging temperature sensitive building materials.

Commercial pressure washing equipment should deliver enough volume (usually 3-5 GPM) to flush away dislodged contaminants, rather than simply spreading them around.

Strategic Pressure Cleaning Areas Post-Storm

The highest return on investment for mold prevention comes from targeted pressure cleaning of specific vulnerable areas following storm events. By prioritizing these critical zones we can make sure resources are spent wisely and on the highest risk areas.

Exterior Walls and Siding

Commercial buildings have special concerns with the vertical surfaces, particularly the lower portions where splash back occurs during heavy rain. Different approaches can maximize effectiveness for different building materials.

• Medium-pressure washing (2000-2500 PSI) is required for cleaning brick and masonry surfaces. Specialized masonry cleaners should be used to effectively remove organic residue while protecting the mortar from damage.
• Lower pressure settings (1200-1800 PSI) are required for vinyl and aluminum siding to prevent warping or denting, detergents will remove the microscopic layer of organic material in which mold establishes.
• To avoid surface erosion, stucco and EIFS (Exterior Insulation Finishing Systems) require gentle pressure (under 1500 PSI) with wide angle spray patterns to remove contaminants.

Areas to pay particular attention to are beneath windows, around door frames and where different materials meet as these transition points will trap moisture longer than surrounding surfaces.

Roof and Gutter Systems

The roof assembly is the most vulnerable and potentially damaging area for mold establishment. Pressure cleaning protocols for this zone are:

• Removing organic debris from gutters and downspouts that create moisture trapping dams
• Appropriate pressure washing (usually 1200–2000 PSI) of roof surfaces to remove accumulated organic matter
• Specialized roof-cleaning biocides that are applied to provide residual protection against fungal regrowth
• Clearing drainage pathways of debris to ensure proper drainage
  

Technicians should work with roofing professionals to coordinate pressure cleaning on flat commercial roofs to make sure it doesn’t destroy membrane integrity or void warranties.

Hardscape Surfaces

After storms, concrete walkways, driveways and other porous hardscapes become important mold reservoirs.

The following surfaces require:

• For penetrating porous structures, higher pressure settings (2500 – 3500 PSI)
• Detergents that penetrate concrete’s microscopic pores and are surface appropriate
• Correct technique to maintain consistent distance between nozzle and surface
• These areas are given special attention where moisture evaporates more slowly

Areas of Outdoor Amenities

Storms are a great way to get mold growing on wooden decks, outdoor furniture and recreational equipment that are porous and always exposed.

What these areas need is:

• Lower pressure settings (1000-1500 PSI) are used to avoid wood fiber damage.
• Brighteners and mild biocides in wood specific cleaners
• Pay close attention to joints, connections and undersides where moisture likes to linger
• After surfaces have fully dried, follow up application of appropriate sealants
  

Through systematic treatment of these areas per material specific protocols, facility managers can break the mold establishment cycle before colonization occurs.

Timing Is Critical: When to Act

Surprisingly, the window of time for effective preventative pressure cleaning is very narrow after storm events. This critical timeline helps facility managers develop response protocols that are as effective as possible and as inexpensive as possible.

The 72-Hour Window

Mold prevention is most effective when it is done within 72 hours of moisture exposure and industry research shows that this holds true.

The creation of this timeline results in three distinct response phases:

1. Optimal: Within 0-24 hours spores have little opportunity to establish. At this stage pressure cleaning achieves near complete prevention with minimal chemical intervention required.
2. Standard: Germination begins but colony establishment is limited to 24-48 hours. Antimicrobial applications are more important for pressure cleaning, but it is still very effective.
3. Marginal: In a window of 48-72 hours early colonies are formed, but have not penetrated deeply into substrates. Though pressure cleaning effectiveness decreases, it still prevents major remediation requirements.

After 72 hours, pressure cleaning becomes remedial rather than preventative and the levels of chemicals, pressures and often follow up treatments increase significantly, raising costs and complexity.

Weather Considerations

Strategic timing must also account for weather conditions following storms:

• Do not pressure clean in periods of high humidity (above 80% RH) as surfaces will dry too slowly and may re introduce moisture problems
• Clean when it is daylight and the temperature is above 60°F to encourage rapid drying
• Think about wind conditions so that overspray doesn’t hit recently cleaned surfaces
• Allow surface drying time adequate before the next anticipated rainfall

Resource Allocation

If a facility has limited personnel or equipment, clean based on:

1. Locations where organic debris was visible.
2. Less direct sunlight on the north facing surfaces.
3. Architectural elements most susceptible to mold damage are high value architectural elements.
4. Contaminants introduced into building systems through surfaces near HVAC intakes

Commercial pressure washing providers should develop standing service agreements with facility managers to be able to respond quickly after storm events. Response times, scope of services and pricing structures should be spelled out in these agreements in such a way as to recognize that timely intervention is preventative in nature.

Preventative pressure cleaning is executed within these critical timeframes and typically costs 60-80% less than remediation of established mold problems and offers superior protection for building assets.

Conclusion

One of the most effective and economical methods of preventing mold and mildew growth after a storm is pressure cleaning. With knowledge of the science of fungal establishment, identification of vulnerable areas and timely intervention protocols, facility managers can protect both physical assets and occupant health.

Effective implementation of the above require the following key takeaways:

1. Know that mold prevention is an action that needs to be done within 72 hours of moisture exposure.
2. Adjust pressure, chemical treatments and techniques to the particular building materials.
3. Focus on high risk areas such as exterior walls, roof systems and porous hardscapes.
4. The best way to ensure that you have a clean and well maintained facility is to establish standing service agreements with qualified pressure washing professionals.
5. Preventative pressure cleaning should become part of comprehensive facility maintenance programs.
   

Adopting these evidence based approaches will allow commercial property managers to substantially reduce maintenance costs, increase building component lifecycles, maintain property values and protect occupant health. Preventative pressure cleaning offers a clear return on investment in the challenging post-storm environment and mitigates multiple categories of risk.