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Photograph of severe mold and flood lines in a basement (C) Daniel Friedman Mold-resistant Construction Methods, Products & Materials

Mold resistant construction practices: clean up existing mold, repair & build to avoid future mold problems: this article describes how to prevent mold growth in buildings. We discuss priorities of action to avoid indoor mold contamination after building flooding or wetting from roof or plumbing leaks.

Here we discuss how to respond quickly to building floods to avoid a mold problem: what steps to take, in what priority. How to move furnishings or possessions from a flooded home to a new or temporary location without bringing along a mold or contamination issue.

How to recognize cosmetic molds to avoid unnecessary mold remediation cost.

Recommended construction details in a new or flood-repaired building and Interior Maintenance to Avoid Mold - Building maintenance tips to avoid indoor toxic mold contamination. How to prevent mold in buildings - construction details and choices of materials to prevent toxic mold. Building and HVAC recommendations to minimize mold problems in hot humid climates

We distinguish between harmless cosmetic mold and mold that needs to be removed, and we outline both construction and building maintenance details that will help prevent future mold growth in a building.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Priorities for Preventing Indoor Mold Contamination in Buildings

Photograph of flooded file cabinetsAll mold is everywhere, all the time, according to one of our mold mentors (Dr. John Haines), an experienced mycologist.

And as we describe here, many building materials and furnishings, if damp or wet, easiluy support mold growth.

To understand the mold-friendliness or mold-resistance of building materials we must look at the material itself, its constituents, but also at coatings, binders and glues used in its preparation for use (Viel 2019).

Critical in mold-resistance or mold-friendliness of building materials, as we see in materials such as gypsum board or drywall, the moisture gradient in the material determines not only its vulnerability to mold growth, but even to the distribution of mold genera/species across the material as moisture levels vary. (Pasanen 2000) (Johansson 2012).

Own research [DF] SAMPLING DRYWALL offers example of three different molds on drywall at different moisture levels and heights from a wet floor. Moving a mold sample location just a few inches higher from the floor finds completely-different mold genera/species!

We start by addressing the question: how do we prevent a mold problem in a building?

We avoid or quickly correct conditions that invite problem mold colonies from growing indoors.

In areas subject to high humidity, wet soils, rain, freezing weather, or other conditions that encourage high indoor humidity, building leaks, poor building ventilation, or other conditions that tend to produce indoor mold and its potential harmful effects and high costs, it is possible to reduce the chances of a future mold problem.

Article Contents

Building Leak or Emergency Flood Response Procedures to Avoid Mold

Here are our recommendations for emergency response to building floods, burst pipes, sewer backups, roof blow-offs or other sudden catastrophic soaking of buildings.

These suggestions are based on 30 years of experience in construction, construction inspection, and our indoor air quality and mold investigations and laboratory testing. Additions, corrections, and content suggestions for this list are invited.

  1. Respond immediately to building leaks and floods.

    This means within 24-48 hours all of the critical steps need to be taken if you want to maximize the chance of avoiding a costly mold cleanup project. This topic will be expanded in detail at this website (coming). Basically:
    • First priorities: Before entering a building that has been flooded review see

      FIRST PRIORITIES: WHAT TO DO AFTER A BUILDING HAS BEEN FLOODED
      to address life, health, and safety concerns.
    • Stop the water entry
    • Remove standing water
    • Remove wet carpets, furniture, and boxes of wet stored items
    • Remove floor trim and lower portions of walls (such as drywall or paneling) (at least 12") and any wall insulation, in rooms where the floors were wet or flooded.
    • Remove upper portions of wall coverings (drywall or paneling) higher than 12" if these areas are wet, or if water entered the wall cavity from above.
    • Remove ceilings that have been flooded from above
    • Remove wet materials (such as areas listed above) until you find a 12" or greater area of dry clean margin.
    • Use dehumidifiers, fans, heaters, to dry the exposed building areas and surfaces.
    • If mold is already visible or suspected, use containment to avoid air movement from the damaged (moldy) area to other building areas. Containment generally means negative air and poly plastic barriers.
    • Also see FLOOD-CAUSED MOLD, PREVENTION

      or if mold is already present,

      see the MOLD CLEANUP GUIDE- HOW TO GET RID OF MOLD article series
  2. Keep unwanted outside water out of the building.

    This means attention to the roof drainage system (gutters and leaders), surface drainage, and at some sites, unusual levels of ground water. In buildings where we find recurrent basement water entry, most of the time the underlying cause is inadequate maintenance of gutters and downspouts, with roof spillage against the foundation.

    Preventing indoor mold by keeping outside water out also means proper construction of all exterior components, roofing, siding, windows, doors, trim, steps, patios, exterior light fixtures, even downspout straps, to keep water out of building walls and cavities.

    See VAPOR BARRIERS & HOUSE WRAP for a discussion of vapor barriers behind vinyl siding.

    The importance of flashing and house wrap on conventional construction pales next to the importance of property detailing when problem-prone building exteriors such as EIFS Synthetic Stucco are used since if workmanship is not exactly correct with those materials leaks into the building cavities trap water and often lead to costly damage, rot, or mold.

  3. Humidity Control:

    Maintain Proper Indoor Humidity Levels to avoid mold.

    See INDOOR HUMIDITY TARGET in order to avoid a mold problem?

    Also see VENTILATION in BUILDINGS.
  4. Leak Prevention:

    proper roofing and flashing details are critical to avoid longer term building leaks at the roof and at other building penetrations such as windows, doors, plumbing vents. Indoors, replace corroded plumbing traps, use burst-resistant washing machine hoses and fixture supply risers. When possible, turn off water when leaving a building vacant for some time.

    See WATER ENTRY in BUILDINGS.
  5. Mold-resistant Building Materials:

    should be used where possible, especially in high-risk areas such as basements and bathrooms.

    See MOLD RESISTANT DRYWALL ? You Must Be Kidding!
  6. Mold-Friendly Building Materials:

    should be avoided in high risk areas. Do not put mold-friendly construction materials (stuff on which mold grows readily) into damp areas. In our experience this means the items listed

    at CONSTRUCTION DETAILS TO AVOID MOLD in a new or flood-repaired building
  7. Ventilation: to avoid indoor mold, proper venting avoids build-up of high moisture in building cavities and avoids, in freezing climates, leaks into building cavities from ice dams. See our discussion of attic venting and under-roof ventilation

    at ROOF ICE DAM LEAKS

    and see our discussion of bathroom ventilation fans, ducts, and indoor moisture control

    at BATHROOM VENTILATION CODES SPECS.

    Crawl space ventilation and dryout steps are discussed

    at CRAWL SPACE DRYOUT

    Also see VENTILATION in BUILDINGS - our home page for this topic.

Avoid Bringing Problem Mold Into a Building

How to move furnishings or possessions from a flooded home to a new or temporary location

If you are moving items out of a home that has been flooded and if that building has become visibly mold-contaminated, there is a significant risk that you will be bringing mold-contaminated dust or even active mold colonies from the flooded building into the new one.

The best approach is to remove moldy furnishings or other possessions from the flooded building, have them cleaned, and then bring them into the new building.

Pressure Treated lumber"

which is sold as resistant to rot and resistant to wood destroying insects is very often not only wet when purchased, but is often mold contaminated with several species of Penicillium sp. or Aspergillus sp.

We confirmed this condition by a survey of building materials at several lumber suppliers in New York, using tape samples of visible mold on the surfaces of these products.

When using pressure-treated lumber for interior framing,

clean off any visible mold. Simple power-washing would suffice. This step is not necessary and would be inappropriate for the same lumber when used outdoors, such as for a deck or an entry stair.

But inside, such lumber may be used for sill plates or in some cases I've seen it used to re-frame a rotted floor over a wet crawl space. Importing a large Aspergillus sp. colony on the floor framing surface over a crawl space provided an immediately-detectable high level of airborne Aspergillus sp. in the room above this area, as these spores move easily in convection air currents moving from the crawl area up through the building.

How to Avoid Unnecessary Mold Cleanup Expenses - Harmless Cosmetic Mold

As long as we are discussing not bringing mold into a building, it's important to warn against unnecessary expenses cleaning up "cosmetic-only" molds such as black mold commonly found on kiln-dried lumber which has been exposed to wetting in transit or storage.

Usually this is a cosmetic-only mold in the Ceratocystis/Ophistoma bluestain group. However in a few cases where this "black mold" on lumber was on wood framing later exposed to flood basements or crawl spaces, I've also found problematic mold growing mixed with this cosmetic inhabitant.

See MOLD APPEARANCE - STUFF THAT IS NOT MOLD

and review BLACK MOLD, HARMLESS

Interior Construction Product Installation Details to Reduce Mold-Risk

Interior Maintenance to Avoid Mold Suggestions from the U.S. EPA

This list based on a shorter EPA list, with additions and edits by the author.

-- Initial Source: expanded and edited from Mold Prevention Tips U.S. EPA. http://www.epa.gov/mold/prevention.html

MOLD RESISTANT CONSTRUCTION - OSHA Advice

The following mold resistant construction advice is from OSHA Guide to Workplace Mold.

Moisture control is the key to mold control. When water leaks or spills occur indoors - act promptly. Any initial water infiltration should be stopped and cleaned promptly. A prompt response (within 24-48 hours) and thorough clean- up, drying, and/or removal of water-damaged materials will prevent or limit mold growth.

Mold prevention tips include:

Questions That May Assist in Determining Whether a Mold Problem Currently Exists

Watch out: Always consider consulting a health professional to address any employee health concerns.

Research on Mold Resistance of Building Materials

Photograph: Moldy drywall supports different mold genera and species at different moisture levels in the same area - Daniel Friedman

Photo: three different mold genera/species dominated adjacent areas of drywall, determined primarily by variations in moisture level: less water higher from the wet floor of a flooded building - detailed at SAMPLING DRYWALL FOR MOLD

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2023-04-01 by Cheryl - hollow clay block construction with plaster proved very mold-resistant

In 1945 this mini house was constructed with hollow clay tiles all the way to the peak of the roof.

Hollow clay block construction in a 1945 mini house (C) InspectApedia.com Cheryl

Photo 1 - [Click to enlarge any image]

The same tiles in the walls were covered with a layer of white plaster, styrofoam over that, then sheetrock.

Now, a roof hole caused the sheetrock to mold.

When I removed a section of the sheetrock and stryofoam, the plaster was PRISTINE. I'd say the vintage clay tiles with plaster have held up really well !

Photo 2 shows after sheet rock and styrofoam removed from the plaster over the old hollow clay tile. PRISTINE.

Partial demolition of moldy drywall shows no mold growth on plaster atop hollow clay block walls (C) InspectApedia.com Cheryl

Photo 3 is the moldy sheetrock that sat on that plaster-covered clay tile for 2 years, and NONE of the mold transferred to the plaster-clay tile. I'd say that's a great vintage product.

Mold growth on gypcum board over plastrer & clay block walls  (C) InspectApedia.com Cheryl

On 2023-04-01 by InspectApedia Editor (mod)

@Cheryl,

These are great photos that illustrate your point: some building materials, including traditional hollow clay tile walls coated with plaster, are far more mold-resistant than more-modern wall coverings such as drywall.

I've seen similar results across many building inspections and mold investigations. Particularly, the paper on drywall is mold-friendly, even in more mold-resistant drywall, and also I think that the moisture uptake of gypsum board is a bit greater than plaster.

I also think that the chemistry of plaster is a significant contributor to its mold resistance. It's not "mold proof" but invariably we see less-extensive mold on plaster surfaces than on wood, drywall, wallpaper, etc.

Please tell us the location of the building: country and city would be enough.

Continuing: these articles may interest you

MOLD RESISTANT CONSTRUCTION - you are on thiis page - I'll copy your photos and comments to that page as there your notes may help other readers.

DRYWALL MOLD RESISTANT https://inspectapedia.com/interiors/Mold_Resistant_Drywall.php

and this PhD thesis

Sedlbauer, Klaus. PREDICTION OF MOULD FUNGUS FORMATION ON THE SURFACE OF AND INSIDE BUILDING COMPONENTS [PDF] Fraunhofer Institute for Building Physics (2001): 75-141.

I'd add that it's interesting that gypsum-board exterior building sheathing, often used behind brick veneer walls that leaked, was also rather mold-resistant, perhaps because of measures taken to make it moisture/water resistant.

See that material described at

SHEATHING, GYPSUM BOARD 

DF

Question: Best plan for removing mold on wood flooring and ceilings & preventing its reappearance

Our builder is constructing a log cabin for us during the hot, moist summer months. The roof has not been fully completed so the interior structure has been exposed to many afternoon rains (as of August 15, 2011).

Tongue and groove eastern white pine flooring provides the flooring for 2nd floor as well as ceiling for 1st floor. Both sides of the T & G will be visible in the completed log cabin. Dark staining and spotting from mold/mildew growth has appeared on the T & G flooring in many, repeat...many, places and needs to be addressed in a timely and correct manner.

The metal roof will be installed in one week. Windows and doors are not installed yet. What is your recommendation as to the best procedure and plan of action to remediate this unsightly, unhealthy, and disturbing occurrence? - Brenda Eller

Reply: After Building Dry-In, Use Sanding, HEPA Vacuuming, Media Blasting, Use of Clear Fungicidal Sealants & Floor Coatings to remove mold and prevent future mold growth

Brenda you're right that white pine T&G flooring easily supports mold growth, particularly when wet and before it has received any finish coating.

The building has to be at the dry-in state so that you can dry out all interior materials and keep them dry, else cleaning costs and effort may be wasted.

If the upper side of your T&G flooring is to be sanded before finishing, that'll do the trick to remove problem mold on the upper floor surfaces.

The under-side can also be wiped, & HEPA vacuumed, but I suspect that won't remove stains nor even mold left in hard-to-reach crevices. If mold is left in flooring crevices it will sometimes reappear below a coating, making future cleaning still tougher.

So you might want to consider cleaning the underside as well as other irregular surfaces that are moldy using media blasting.

At MOLD CLEANUP GUIDE- HOW TO GET RID OF MOLD you'll see in that article series an article on using media blasting to clean surfaces

MOLD CLEANUP - MEDIA BLASTING along with some photos of what an impressive job that method can perform.

When surfaces are clean if you coat them with two or even three layers of clear polyurethane that will reduce moisture up-take in the wood and thus resist future mold appearance. If wood is to be stained of course you'll do that before applying poly.

There are also clear sealants used by some mold remediation companies that might work well on the under-side of floors (ceilings) where the wood is to be left exposed. I wouldn't use those on the walk-on surfaces unless the manufacturer agrees that their sealant is hard enough for floor traffic.

Clear fungicidal sealants suitable for use where wood ceilings or framing are to be left exposed are illustrated

at FUNGICIDAL SEALANT USE GUIDE

Question: how can we prevent mold growth in timeshare units located in the Caribbean?

La Manzanilla, Mexico Pacific Coast © D Friedman at InspectApedia.com Hello, we are a timeshare company based in the Caribbean. The area is extremely humid thus we have a lot of mold issues. Are you aware of any remedy/product available to prevent mold from growing also on lampshades and wall paintings?

All our lampshades become moldy after a period of time. We were wondering if it exist any type of spray that can act as a coating.

Thank you for the information you can give us. - D.C.

Reply: recommendations for preventing indoor mold in a hot humid climate & for minimizing the risk of mold damage or hazards

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with indoor moisture and moisture control - the gating factors in the mold growth problem you describe.

Our photo above illustrates several types of buildings located in a hot humid climate in la Manzanilla on Mexico's West coast.

We did not find significant mold contamination problems in these structures, as I explain further below.

Because all mold is everywhere all the time, when the indoor environment is particularly friendly to one or several mold genera/species that like to grow on common building materials and surfaces (drywall, carpets, furnishings, painted surfaces, lampshades, wall paintings), it will grow there.

What those building and building-contents loving molds need are food, air, and water. Of those three, the most effective approach, as it protects so many materials against mold growth, is to stop building leaks and keep indoor humidity levels down below 50% (perhaps even 40% in some cases).

If you do not use indoor cooling and/or dehumidification, then indeed what's left is to

La Manzanilla restaurant (C) Daniel Friedman
  • Indoor ventilation,

     where cooling and dehumidification are not being used, is a more tricky question. If we bring hot humid air into an interior space that is cooler than the outdoors, moisture may condense on or in interior surfaces and materials, making the mold problem or mold risk worse.

    On the other hand, if indoor and outdoor temperatures move together, such as occurs in living quarters that are completely open to the outdoors in some tropical areas, increased use of ventilation and fans may actually help reduce risk by improving the indoor evaporation rate.

    In our photo (left) I'm enjoying coffee in a restaurant on Mexico's Pacific coast (La Manzanilla).

    Construction is so open to outdoor air that the building and its contents remain very well ventilated. I did not see any mold problems in this building nor on its contents, even though it is located in a hot humid climate.
  • Inspect regularly for mold contamination and act promptly to clean up the mold -

    that means removing it from surfaces that can be cleaned, and disposing of stuff that can't be cleaned, as well as checking for unusual causes of mold growth such as leaks or improperly functioning air conditioners or dehumidifiers.

    Regular inspections can be particularly important in your circumstances because of the combination of a very humid environment, high temperatures, and living units that may remain unoccupied for long periods, risking extensive and thus expensive mold contamination if a problem is left un-checked.
  • Mold on artworks:

    We have assisted several museums & curators with mold diagnosis, cure, & prevention on works of art.

    Beyond the control of indoor humidity that we've already discussed, specific steps you'll want to take will depend on the materials used and the value of the paintings or works of art in your buildings.

    No valuable artwork should be sprayed or coated with a fungicidal sealant, certainly not before consulting with an expert art conservationist.

    However it may be possible to frame, enclose, or treat the back surface of some paintings without damaging the work itself nor impinging on its artistic or monetary value. Take care to distinguish between mold growth and other types of moisture-damage to artworks such as extractive bleeding stains.

    Other artworks we have examined suffered severe mold damage, including a wide range of media such as paper-based prints and lithographs or etchings and oil paintings on canvas. Some examples of mold contamination of art works that we've examined are found

    at ARTWORK MOLD CONTAMINATION.

    At  ART CONSERVATION - Cultural Heritage and Aerobiology we describe a text that offers some help in controlling mold and other sources of damage to paintings as well as other cultural artifacts.

Watch out: There may also be health risks to some of your occupants, particularly those with asthma, mold allergies, the elderly, infants, or people with compromised immune systems.



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