# Old house, plaster walls, mildew--what to do?!



## joecaption (Nov 30, 2011)

Siding is never sealed, the vapor barrier needed to be on the inside walls.
You have cold air in those walls that's causing condensation when it hits the warm moist air inside the home.
Very likely a home that old has balloon framing which would mean those walls are open from under the house all the way to the attic.
The fix is fire block the walls at the top and bottom, insulate the walls, get an exhaust fan in that bathroom ASAP.
Attic needs to be air sealed and at least R-50 of insulation (that's 12") proper roof venting,
And R-19 under the house, insulate the rim joist.
Do those things and your heating savings would more then pay for the materials in a short time.


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## Nestor_Kelebay (Jun 17, 2008)

Two fast easy effective solutions:

1. Repaint your walls with a mildew resistant paint.

Probably the fastest and easiest way of getting rid of the mildew problem in the affected rooms of your house is to paint the walls in those rooms with a mildew resistant paint like Zinsser's PermaWhite Bathroom Paint which you can buy at Home Depot as well as most home centers.









PermaWhite comes in both satin and semi-gloss and can be tinted to any off-white or pastel colour. Zinsser may have changed their labels recently, but the above is what I remember buying last time I bought the stuff. They may have a different label now.

Bathroom paints work by a process called "leaching" whereby the chemical mildewcide that's added to the paint gradually leaches out of the paint film whenever there's water or even high humidity on one side of the paint. So, even high humidity in a bathroom will cause the mildewcide in the paint to migrate to the surface of the paint where it kills mildew spores before they have a chance to grow.

Mildewcide leaching is affected by a lot of different variables, including the gloss level of the paint. If the rate of leaching is too slow, then mildew will grow on the paint for lack of sufficient mildewcide. If the leaching rate is too high, then the paint will only be mildew free for a short period until the mildew reserve is depleted from the paint film. This is why someone who goes to a Sherwin Williams store and just buys a bag of Mildex to throw in their paint before they have it shaken is fooling themselves into thinking their paint will be mildew resistant in any reasonable way. As likely as not, the mildewcide will leach out of their paint too quickly or not quickly enough. This is why paint companies like Zinsser do experiments to measure the rate of mildewcide leaching out of their paint film. The objective is to achieve the slowest rate of leaching which is still 100% effective in killing all the mildew spores on the paint. Zinsser guarantees their Permawhite bathroom paint to be mildew free for a period of 5 years, but my experience with it is that if you put on several (two or three) coats of the stuff, it'll remain mildew free for closer to 15 years.

Also, since the mildewcide in the paint is highly soluble in water, it's not a good idea to clean PermaWhite paint with water. The cleaning water you use will clean the mildewcide off the surface of the paint, thereby removing mildewcide with is what's preventing the mildew from growing. If you have to clean it, clean only the area that needs cleaning.

2. Stop having showers. Have baths instead.

Mildew is like anything else in that it needs food to survive and multiply.
In the case of mildew, the food it eats is the oils in the plant oils that bar soap is made of. Most bar soaps are made by reacting plant oils like Palm oil and Olive oil (from which the Palmolive company gets it's name) with a strong alkali in a process called "saponification". In that saponification reaction, the vegetable oil triglycerides are broken into separate fatty acids and and a sodium ion from the alkali attaches to the fatty acid to make it soluble in water. Most of the hydrocarbon chain of the fatty acid is still in the soap molecule, and this is what provides the food source for mildew.

By using bar soap to lather yourself up, and then spraying your body down with water, you put a mist into the air that contains those soap molecules, and they coat the entire inside of your bathroom, and most likely the surrounding rooms as well, thereby providing mildew with a steady source of food.

By having baths instead, the soap molecules tend to either remain dissolved in the water or stick to the sides of the tub in the form of soap scum. Either way, the soap doesn't get all over the walls of the bathroom like it does when you have a shower.

Clean your walls of soap by using a general purpose bathroom cleaner, and then have baths instead of showers. You will be denying the mildew a source of food and thereby preventing it for flourishing in your house. Effectively, you'll be turning your bathroom into a desert for mildew because of the lack of available food.


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## SeniorSitizen (Sep 10, 2012)

Sometimes we need to change some of our life style habits with the seasons. An example, we need to cook meals on top of the range as much as possible to increase moisture in our house where you would be better to bake meals in the oven as much as possible. 

Showers and baths - remove the damp bath towels from the area and wipe the wet surfaces down to get the moisture from the room. Realizing it isn't normal to put those items in the dryer but it will definitely remove the water and expel it from the troubled areas. These measures may not completely solve the problem but will help.


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## Nestor_Kelebay (Jun 17, 2008)

If I were the OP, I'd start by cleaning his walls and ceilings with bleach diluted with 5 parts water, and then rinse the walls down with clean water. In doing this kind of work, I find a wet/dry vaccuum cleaner with a squeegee nozzle helpful. I just spray the cleaning solution onto the wall or ceiling, agitate with a bristle brush on a painting pole, and then use the squeegee to vaccuum the soiled cleaner off the walls and ceilings. Then repeat with clean rinse water. Obviously it's important to cover any flooring like carpet that could be damaged by the bleach.

Then, everything he does beyond that will be a step in the right direction now that he has better knowledge on how to deal with the mildew.


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## El Barbón (Nov 25, 2013)

Hem. Might not have made it clear in the original post, but these pictures are from the rooms that *flank* the bathroom. Bathroom itself is mildew-free (huzzah for the dehumidifier and old lead-based paint!), and the pictures are of the exterior corners of the two rooms on that side of the house.

I know that siding isn't supposed to be *sealed*, but how tight should it be? The house isn't balloon-framed, because I can see the framing from the upstairs, where we pulled out the old wallboard while restoring the half-story. We try to limit showering, especially during the winter, and sometimes run the dehumidifier in the kitchen when we're washing a bunch of dishes or cooking/baking a lot (plus, the kitchen has a fan).

I guess what has me stumped is how we're going to prevent the problem in the future. Obviously it's got to do with temperature; one year, I was out of town when the storm windows should have gone up, and we had crazy mildew problems until they went in, especially since the furnace was out of commission and they were heating with space-heaters. But this last winter, we didn't even get much condensation on the windows, which is a pretty good barometer of how you're doing, temperature-wise, in an old house, I thought. What's killing us is whenever anything's close to the exterior walls in these two rooms, one in particular. If the inside temperature is comfortable enough, why are we getting so much mildew on the walls? I grew up in an old midcentury house that wasn't insulated, with aluminum windows, and we used to get *ice* on the inside of those some winters. Mom and Dad set the thermostat to "off" every night, and it was pegged around 65 during the day--yet we never had these kinds of moisture problems there. I know this is not a lot to go on without actually getting to see it first-hand, but I'm stumped. Short of pulling the wall apart and putting in some kind of vapor barrier, I don't know what to do. The house never *feels* that humid, and even in the basement, things don't get mildewy unless they're clothes stuffed in a cardboard box--even then, they just get musty.

How the heck are we to get the humidity problem licked?


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## Windows on Wash (Aug 30, 2011)

Whats the venting and insulation like in the attic.


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## SeniorSitizen (Sep 10, 2012)

QUOTE: What's killing us is whenever anything's close to the exterior walls in these two rooms, one in particular. If the inside temperature is comfortable enough, why are we getting so much mildew on the walls?
***************************************************
Monitor the wall temperature and compare that temp. with the dew point temperature of your interior air.


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## El Barbón (Nov 25, 2013)

Attic is well-ventilated, with a ridge vent and plenty of inlets. It's uninsulated too, which we're taking care of as we finish the upstairs; it's got small attics behind the knee-walls on either side of the half-story.

I'll see what the wall temp looks like tonight--even though they don't feel especially cold to the touch, I'll see if I can get an actual measurement.


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## Nestor_Kelebay (Jun 17, 2008)

If the humidity is not causing any problems other than the mildew growth on exterior walls, then you can still use a mildew resistant paint to prevent that from happening.

A mildew resistant paint will prevent mildew growth on the walls and ceilings in ANY room, not just bathrooms.

Would you be happy to just be rid of the mildew even if it didn't involve lowering the humidity of the house somehow?


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## El Barbón (Nov 25, 2013)

Nestor_Kelebay said:


> Would you be happy to just be rid of the mildew even if it didn't involve lowering the humidity of the house somehow?


Yes. Yes we would, which is why as soon as the upstairs is finished, we're going to start in on those rooms and repaint. If nothing else, mildew-resistant paint is a good first step!


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