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Cabinet water damage from dishwasher (C) D Friedman Mold-Contaminated Kitchen or Bathroom Cabinets
Cause, cure, prevention of mold on or in wall or base cabinets

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Kitchen & bathroom cabinet mold growth:

What are the causes of mold contamination found on, in, under or behind wall & base cabinets? Aside from obvious leaks, where else might water or moisture come from in cabinetry? What is the best way to clean or repair wet or moldy cabinets?

This guide to inspecting, installing, & repairing kitchen & bath cabinets & countertops describes common defects found in kitchen or bathroom cabinets - problems that can be found by visual inspection.



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Water Damaged & Moldy Kitchen or Bath Cabinets

Cabinet rodent feces (C) D Friedman

A small moldy patch on a particleboard cabinet base (less than 1 sq. ft.) such as shown at the top of this page is unlikely to be a significant health hazard in a building, though it could bother someone with sensitive mold allergies or who is asthmatic. [Click to enlarge any image]

There may be more hidden mold below the cabinet base.

in this photograph of the cabinet base interior we notice that the mice don't seem disturbed by water, leaks, and mold - though their droppings make the cabinet unsanitary for food storage.

Below we illustrate another minor mold contamination case, due to water that leaked from a nearby shower to beneath the vanity base.

The vanity was replaced and the new unit first coated with a clear sealant on its hidden surfaces, then caulked at the floor and walls to keep water out of its hidden spaces.

But mold growth behind wall or base cabinets can be quite extensive.

Below: I've pulled a bathroom vanity base away from the wall for plumbing and other repair work.

Photograph of inspecting below a bath vanity for hidden mold.

in our next photo (below) and looking on the drywall that was previously covered by the vanity side and back, you can see mold contamination on the lower bathroom walls that were previously hidden by the cabinet back and side.

While the ceramic tile covering this floor, including below the base cabinet, is not normally a mold-friendly material, organic dust and debris that may accumulate under a cabinet can itself also hose mold growth if that space is also damp or wet.

Photograph of inspecting below wallpaper for hidden mold.

After replacing or cleaning moldy surfaces where the cabinet is to be reinstalled, we cleaned the hidden surfaces of the vanity base using ordinary household cleaner.

When the base was thoroughly dry we sealed its underside with spray shellac (quick drying, convenient) to improve its moisture resistance and to thus make it less mold friendly in the future.

When we reinstalled the vanity base we also took care to seal it carefully both at the sink top splashboard and around the vanity base on the floor so that water spilled in those areas would no longer run under the cabinet and into a mold-friendly space.

Mold behind cabinets or on their other hidden surfaces may be both severe and totally hidden if a home has been flooded for any reason, as we illustrate with the photos below, showing mold on the previously-hidden sides of kitchen cabinets.

More examples of mold growing on just about anything in buildings can be seen at MOLD GROWTH on SURFACES, PHOTOS.

Photo of mold hidden on the wall side of kitchen cabinets, after cabinet removal © Daniel Friedman Photo of mold on previously hidden surfaces of kitchen cabinets and range hood(C) Daniel Friedman

It would have been a mistake to leave these cabinets mounted to the wall of the home where they were found, even though mold was not visible on the room side of exposed wall surfaces.

Further investigation of the wall cavity behind where these cabinets had been mounted confirmed that the cavity side of the wall needed to be cleaned as well.

Leaks into kitchen or bath cabinets can occur in surprising places, as water can travel inside a building wall or along a floor where it passes into hidden spaces such as the interstitial space between a cabinet back and the building wall, or the cabinet base and the floor. A result can be hidden mold contamination.

My photo above shows that leaks in or below the dishwasher were affecting the lower left side of the kitchen base cabinet next to the dishwasher. Until the dishwasher was removed for replacement the extent of leakage was not so obvious.

Cabinet water damage from dishwasher (C) D Friedman

Below is a delaminating sidewall of a kitchen base into which water had leaked, and if you enlarge the image you'll see water on the cabinet base shelf.

Cabinet water damage from dishwasher (C) D Friedman

Expect to find mold on hidden wall or floor cabinets on hidden surfaces if a building has been flooded or subject to extensive leakage or wetting due to extinguishment of a fire.

The most common location of water damage to cabinets is of course at sinks or at the sides and bottoms of base cabinets adjacent to a leaky dishwasher (our two photographs above).

When the cabinet side or floor is badly water damaged the only durable repair is to either replace the cabinet or base entirely or to remove and replace or re-build its damaged components.

Kitchen base cabinet interior floor and back repairs (C) Daniel Friedman

Illustrated in the kitchen base cabinet photo above, I've replaced a water damaged cabinet interior floor and covered-over a cleaned-up but water damaged area on the cabinet's rear wall.

Often we can remove sagged, water-damaged, moldy particleboard used as a base cabinet's interior floor and shelving. The new floor is tacked down or screwed to cleats so that in the future if we need to remove it to inspect, clean, or repair the space below it's easily accessible.

[Click to enlarge any image]

After making sure we have installed sufficient cleats or support we then install a new base floor and shelving using birch or other decent quality plywood that in turn is further coated on all sides with a clear lacquer or other sealant.

Below we take a different and easy approach.

Repair to water damaged base cabinet (C) Daniel Friedman

Look at the interior floor of the bath vanity cabinet shown above. A previously-water-damaged particleboard cabinet floor was simply cleaned, left in place, and covered-over with a finished, solid wood floor giving a clean, attractive finished surface.

Watch out: all of this base cabinet repair or replacement will be a wasted effort if we don't find and fix the leaks that caused the trouble in the first place.

See SINK LEAK DIAGNOSIS & REPAIR for an example: replacing a leaky kitchen strainer basket that was leaking into the cabinet base.

Question: clogged kitchen base weep openings cause mold trouble?

Mold on base cabinet floor (C) Daniel FriedmanI have a base cabinet that has mildew/mold in it, it is not near a water source. Could it be from blocked weeping holes? No other cabinets are affected and this base cabinet is not next to sink or d/w. Also, the mold/mildew appears to only be on the shelf and the wall of the cabinet that is not attached to the wall of the house.

It is perplexing as we can't figure out why only certain places in the cabinet are moldy, other than when I searched outside I noticed the weeping holes had dirt in them.

I can unblock the weep holes should I pour some bleach in them (only 2) and if so how much? My brick house is 4 years old built on a slab.

Thank you, Dinah - 2017-08-04 This question was posted originally at BRICK WALL DRAINAGE WEEP HOLES

Our photo of black mold on the bottom shelf of a kitchen base cabinet is from our files and is not Dinah's cabinet -Ed. [Click to enlarge any image]

Reply: base cabinet weep openings are not enough to prevent mold growth.

Dinah,

For other readers: here we're discussing weep holes in kitchen base cabinets, condensation, and mold in cabinets, and NOT brick wall weep and drain openings.

Looking at installation instructions for kitchen base cabinets such as units sold under the brands KraftMaid CoreGuard™ and Merillat, whose instructions look almost absolutely identical, we are warned that while the installer is to caulk around pipes that penetrate the cabinet bottom or back, she should not caulk weep holes placed in the interior flat base of the cabinet at its four corners.

If there's mold, at some point the area that supported the mold growth was probably damp enough to encourage that to occur.

The moisture may not necessarily be due to a leak, it could simply be moisture coming from condensation that's trapped in a space with poor air circulation and that gets an inlet of humid air in some building conditions.

I'm unclear about the role of weep holes on your base cabinets and would like to see the cabinets and the installation details (photos via page bottom CONTACT link). But here is some speculation that might help.

However in over half a century of working around and repairing or replacing cabinetry I've not myself come across a situation in which weep openings in a base cabinet prevented mold growth.

If we have an actual water or moisture source sending water or high moisture into an enclosed space, little teensy weep holes won't eliminate the risk nor prevent water or mold damage - too little ventilation passes in and out of our weepettes.

The weep openings might help avoid cabinet buckling or warping from temperature or air pressure changes, but that's speculation too.

I wouldn't pour bleach into the weep openings, since you'd be pouring water (it's not going to be 100% hypochlorite) into the space under the cabinet base where it'll be trapped.

The water content of the bleach solution will wet the area under the cabinet floor, yet the bleach won't be in contact with the (perhaps or even probably) moldy surfaces on the hidden, un-finished under-sides of the moldy cabinet base.

Instead, assuming the cabinet is not so badly water damaged that it needs replacement, you need to clean off the visible mold from the cabinet surfaces using any household cleaner.

If there is no nearby sink nor dishwasher, including via abutting cabinets underneath which water could be passing, then I'd assume something put into the cabinet base was wet, or cool temperatures inside the space are sometimes causing condensation.

Or perhaps there is an exterior moisture or water source from the slab floor below.

Steps to Fix your Moldy Cabinet

Where I've found that situation I've

  1. Taken care to not put wet stuff into the cabinet
  2. Made sure any abutting exterior walls are insulated and not leaking
  3. Added improved air circulation: in real problem cases I've added larger air openings to permit air to circulate in the cabinet (or closet) by installing a vent rectangle opening covered with something sufficiently attractive.

This image below is an example of how we ventilated an enclosed space at a pipe chase next to a cabinet to stop a condensation and sometimes freeze-up problem. .

Air register prevents frozen pipes (C) Daniel Friedman

Details about that approach are at HEAT SOURCES to AVOID FROZEN PIPES

The K&B Cabinet guides at our CABINET INSTALLATION & REPAIR MANUALS mention the weep holes in the cabinet base and warn the installer to keep them clear of caulk.

Also see BROWN HAIRY BATHROOM MOLD for a Q&A on the harmfulness of "hairy brown mold" found in a bathroom.

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Continue reading at CABINET CHOICES, Bath / Kitchen or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see HIDDEN MOLD, HOW TO FIND

Or see MOLD ACTION GUIDE - WHAT TO DO ABOUT MOLD

Or see MOLD CLEANUP GUIDE- HOW TO GET RID OF MOLD

Or see these

Cabinets, Shelving, Casework, Trim Articles

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