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Mold and Mildew Control, Cleaning and Removal

Mildew is not a nice person!

Mildew is a modern annoyance... a growing problem that is unsightly, odorous and unhealthy!  With the advent of super-insulated homes and energy consciousness, mildew levels in our homes have increased.  So the simple question is...  what can we do to kill it, stop it and keep it away?

You can do it... if and only if you are willing to do some work, break a few bad habits and learn a few new ones!

What is mildew and why is it a problem?

Mildew is the generic name for a few types of fungi (itty bitty plants) that grow readily on moist surfaces.  Once it invades your home, it spreads rapidly on surfaces and reproduces itself by releasing airborne spores... the fungal equivalent of seeds.  Mildew growth can deteriorate wood, paper and leather.  It can also live very nicely on paint (it's favorite is latex), penetrating though the paint's pores into the wallboard paper or absorbent plaster below.  It is often found in bathrooms, kitchens, basements, crawlspaces and even attics... anywhere there is high humidity, low ventilation, and a suitable growing medium.  Though heat does accelerate mildew's growth (why the tropical atmosphere of a steamy bathroom is so attractive), some types can grow and thrive at temperatures near freezing!

Mildew is a huge problem with books, magazines and furniture.  Did you ever store books or an upholstered couch in a damp basement for any length of time?  Phew! (Or if you were a fungus, you might retort "Yum!").  The problem is so universal that even libraries have guidelines for book storage to reduce mildew and mold growth.

The lack of ventilation in modern homes because of efficient weatherproofing has decreased the number of air changes per hour.  This in turn increases the average humidity levels in bathrooms, basements, kitchens and laundry areas. Combined with the necessary removal of a potent mildewcide from latex paints... mercury... mildew has become a serious problem on painted surfaces.

Mildew predates humankind and will undoubtedly outlast us. This is painfully obvious to those of us who are allergic to the airborne spores mentioned earlier, as well as people with various respiratory and immune deficiency diseases. For some, mildew can make a home almost unlivable!

Though it is almost impossible to completely eliminate it from your home, you can take some positive steps to control it. We'll touch on a number of scenarios expressed in commonly asked questions that follow, to aid you in taming the mildew menace!

How can I prevent mildew in my bathroom?

By far the most important mildew control remedy is to increase the ventilation in the bathroom. Leave the bathroom door open after you shower or bathe, and use the bathroom exhaust fan. If you live in an older home without an exhaust fan, install one, and be sure it is vented to the outside, or you may transfer your mildew problem to the attic!

Existing mildew on most surfaces can be killed with a mixture of 50% household chlorine bleach with 50% water. Use a hand sprayer to apply it to the surface, allow it to remain for a few minutes or until the blackish, dirty-looking mildew color disappears and then rinse thoroughly with water. If the surface is covered with soap scum, the mildew might be more difficult to kill.  In that case, perform a thorough cleaning first with either TSP, a TSP equivalent or a commercial soap scum remover.  Then use a mildew wash, even if it "looks" as though the mildew is all gone.

There are commercial cleaners that combine bleach with a cleaning product.  I have found them to generally be less effective at killing the mildew so my advice is to keep your killin' and cleanin' separate!

Unfortunately, the mildew will return eventually unless you seal the walls by proper repainting. Mildew attack increases the porosity of the paint film, making reinfestation a certainty. Applying the proper paints after killing the mildew will assure longer-term mildew resistance.

By the numbers...

  1. Kill all mildew using bleach, as described above. Wash all walls with a prepainting detergent such as Soilax. If the ceiling is a spray texture ceiling, do not attempt to wash it or the texture will come off. If the texture is mildewed but still firmly attached to the ceiling, spray the bleach solution, let it dry thoroughly, and then continue to the next step, priming. Get more info on painting spray texture... so-called popcorn ceilings... by clicking HERE. The article will open in a new browser window, so you don't lose this page.
  2. Let the surfaces dry thoroughly and then prime the affected walls completely with one coat of an oil based, fast drying primer such as Kilz.
  3. After the primer is dry, finish painting the walls with two coats using a semi-gloss or eggshell finish latex paint, or a specially formulated bathroom/kitchen paint.  Because of its limited washability, flat wall or ceiling paint is not recommended in bathrooms, especially where it will be directly exposed to water such as around the top of a tub or shower enclosure.
  4. The paint you choose must be treated with a mildewcide which you can purchase at the paint store.  Do yourself a favor... have your paint store add the mildewcide for you before shaking the can... it is difficult to evenly mix the mildewcide by hand!  The exception would be bathroom and kitchen paints which normally have a mildewcide in their formula, making extra additives unnecessary.

Mildewed caulk and grout in tubs and showers often resist bleach and other cleaners.  Why?  Because the mildew is growing inside the caulk or grout !  The only way to fully eliminate it is to remove the old caulk and replace it with a mildew-resistant caulk designed for bathrooms.  Ditto for the grout, except you should replace it with a latex-fortified grout.  These newer grouts are much less porous than old style cement grouts and more strongly resist mildew!

My crawlspace and the area under the floor is covered with mildew.  How can I stop it from growing?

You should view the mildew as a symptom
If there is mildew growth, there is also the chance of moisture damage occurring in the wood framing. Taking the appropriate steps will not only minimize or eliminate the odor but also preserve the value of your home.

Moisture must be reduced and ventilation increased to effectively control mildew in a crawlspace. To that end you must be absolutely certain there is no surface water entering the crawlspace. Look into the crawlspace after a heavy rainstorm for evidence of water. If you find any surface water at all, the following steps will be futile.  You must eliminate it first. Check the gutters and leaders for breaks and blockages. Check the drainage around the house, and make repairs as necessary.  Repair cracks in foundation walls and if necessary coat with a below-grade cement-based waterproofing paint.

Lessen the overall amount of water vapor entering the crawlspace from the ground... This is accomplished by laying a heavy plastic tarp... 5 mil or thicker... over the entire floor.  If multiple sheets are used, they should be folded together at the seams and/or at least overlapped at least 3 feet.  Use stones to hold the plastic down.  This plastic acts as a vapor barrier and will eliminate much of the movement of water vapor from the ground into the crawlspace, with the added benefit of lessening radon infiltration.

Examine the ventilation of the crawlspace...
The amount of ventilation needed is determined by 1) the square feet of floor and 2) the presence or lack of a vapor barrier, as mentioned above. To impress upon you the value of the vapor barrier, look at the following example:

You have an 800 sq.ft. crawlspace. Without a vapor barrier, you would need to install 5 sq.ft. of vent. With a vapor barrier, you would only need to install 1/2 sq..ft. of vent!

As you can see, installation of a vapor barrier lessens the need for ventilation by a factor of 10!   To estimate your own needs, use the following general guidelines:

Without a vapor barrier, the vent area should be 1/160th of the total sq.ft. of the crawlspace.

With a vapor barrier, the vent area should be 1/1600th of the total sq.ft. of the crawlspace.

Remember that your local building code may require more or less ventilation depending on your area's peculiar moisture and weather conditions.  Do a little "hometown" investigating before taking any action!

Other ventilation options...
Depending on the design of your home and the aesthetic appearance of different vent styles, there are different ventilation options. Rectangular or round louvered vents come in various sizes and should be installed on opposite walls of the crawlspace, if possible, to provide cross ventilation. They can be installed through the foundation or between the floor joists through the header. There are also powered vents available, though they are not commonly used (or necessary) except in extreme cases. Visit a home store or lumberyard to see the different types of metal and wood vents available.

Remove any insulation, debris or other items such as wood or fabric furniture that can hold moisture and mildew.

This is especially important if odor removal is a high priority.  Leaving anything in the area that holds the odor can only diminish your results... right?

You could also engage in more heavy duty mildew removal...

A few options would be to spray the walls and ceiling with a mildew-killing wash, either a commercial product or TSP/bleach mix prior to installing the vapor barrier. This can be very sloppy, especially if you have a dirt floor, and definitely unhealthy for man or beast without proper skin and eye protection, forced ventilation, and breathing protection!

Isolate the crawlspace from the rest of the house...

If you do not have insulation in the floor above the crawlspace, install it... Fiberglass insulation with an integral foil vapor barrier can help to isolate the crawlspace from the rest of the house. Install the insulation with the vapor barrier up. Then staple construction grade heavy (minimum 5 mil) plastic sheeting across the joists after the insulation is installed, overlapping all corners at least a few feet.   This will both keep the insulation drier and prevent smelly crawlspace air from infiltrating the house.

If your climate does not require crawlspace insulation, no problem!  Plastic sheeting tightly stapled across the floor joists can be used as a stand-alone remedy and will be just as effective if installed with enough overlap to fully seal off the crawlspace.

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