hi,
my bathroom is small and doesn't have an exhaust fan, so over time mildew has collected on the walls and ceiling. i'm starting preparations for my bathroom renovation, where I'll be tearing out the plaster walls & celing.

i want to be prepared if i tear out the plaster and find the mildew has made its way thorough the plaster and onto the studs and ceiling joists. i have 2 main questions:

1. is this likely?
2. if it did happen, what should i do to get rid of it?

thanks in advance for the help!

 

A mixture of 1 part bleach and 4 parts water should be used to kill it. Humidity feeds it's growth. Wipe down shower walls and any other wet surfaces after bath or shower. This is the reason exhaust fans are now in the code for bathrooms. Good luck.

 

well, i've actually started my renovation project, and tore out all the walls & ceiling, and I think the joists and studs look OK, but some insulation for the roof in the attic has some mold in it, so there was definitely moisture up there.

there are dark areas on the studs and joists, but i'm not sure if its mold (but I'm assuming it is to be safe). i was thinking I'd use the water/bleach mix, and then move my dehumidifier up there and let it run overnight.

how long should I wait until i hang the ceiling and walls? is there a moisture/vapor barrier I should put up under the green board to prevent any mold I may have missed from spreading onto them?

thanks for the help.

 

I am no expert and don't have the answers to everything you needed to know, but since you haven't received another reply all this time I thought I would add a couple of small things I do know about that you might find useful. They are tips for recognizing and dealing with mildew, drying the treated areas, and prepping areas to be treated. I spent years as a painter so I am somewhat familiar with this stuff.

First of all, any time you wash a wall with bleach, TSP, or for that matter even a strong general cleaner, it's important to do it from the floor up - if you start at the top using such cleaners the water will drip down and leave trails as it does so, and those trails will get very very clean and stick out like a sore thumb. I learned this the hard way on one of my first jobs. I was unable to scrub enough to get it to "blend," and it was so distinct that I had to actually do another whole coat of paint! I've had jobs where I was hired to paint only because the homeowner had caused that problem by cleaning the walls ceiling to floor. That expense could have been avoided if they'd known.

If you must start at the top, then at least wet the whole wall first. That will help a lot, unless the walls are very aged and/or have built up grime, smoke stains, etc. You'd think that since bathroom paint is always (or should be) enamel that it would scrub well enough that you could fix it, but no, not always.

Here's how to tell if something is mildew - if you put a bit of bleach on the spot and it bubbles then it's mildew. Other things cause that reaction, such as animal urine on a hard floor. If you put bleach on alge or fungi it will turn white (but not bubble) and if it's just dirt it won't even turn white. Handy little thing to know, since mildew is such a big deal.

There is also a very unique mildew odor, if you can learn to recognize it - maybe you've smelled it at an old library, an historic old fort or museum, a basement, or any spot that gets very little sunlight or heat and maybe also feels a bit humid. In such cases there is a very distinct smell, and if it's strong enough you'll never forget or mistake it again. That's the smell of mildew. Many things LOOK like mildew but are not, but between the smell and that bleach test it's fairly simple to determine.

Regarding dark spots on the joists or rafters, that is the case with water stains, period. What I mean is that it doesn't necessarily follow that mildew grew there too. The stain is permanent, and it will get lighter as it dries but will always be apparent compared to the surrounding wood. (If it caused a stain on your ceiling 20 coats of paint won't cover it, it will continue to bleed through. First spot-prime with a sealer such as Z-Prime, Kilz, or B.I.N and then when you paint it won't bleed. If you begin to notice the stain returning {or any new brown stain, on ceiling or wall}, it's a good idea to trace the stain with a pencil and watch it over time to see if it the brown line goes beyond the pencil mark. This is how you determine if moisture is continuing to come in.)

If you find that the stains on your wood are a bit powdery or you notice any kind of surface substance the non-stained wood nearby does not have then I would give it a quickie with bleach so that all that would be sterilized first, because I would want to remove all the film and wouldn't want contaminated particles to land in other spots and possibly grow more mildew later. I like to use 3-M sanding pads for removing many types of buildup - they can be dipped in wet cleaning solutions and squeezed out and with just a little action they will remove the "stuff" and clean at the same time. Besides, just about every time I use sandpaper on structural wood members (which are usually much rougher than finish lumber) I end up with bad splinters. If you do use any kind of abrasive, don't go higher than a 60-grit, because if you smooth out the area too much the bleach might not penetrate sufficiently. Another method is to blot the spot then use a wire brush - that will both remove any surface substance and provide what we call a "tooth" - a rough enough area to grip a coating or let something penetrate.

As for dry time, this is completly impossible to say due to the variations of each situation. If it's dry there, vented, and the temperature is mild then all that you'll need to dry out are the areas where you put your bleach solution. If that's the case, the drying time isn't very great, and a few hours should be enough (assuming there's any air flow at all).

Personally I like to just get it over with, so I use my heat gun, a cheapo I bought for $20 several years ago. It's really handy for lots of things, but far hotter than one might imagine. It's important to be very careful all around.

I'm too impatient to stand where with a gun until a spot dries, so I set it up in a firm position then go do something else for a brief time. But it MUST be set up properly. Two coathangers will do the job - one to hang over a rafter to make a hook then a second to secure it and shape how I need it. It's essential to ensure that it can't move if I turn away or leave, directed in a position where it will be aimed at the wet spot and not harm anything nearby (attics are dusty, and even one spark could burn down a house), and far enough away from the wet spot that it could not singe the wood, even if it was on and left like that for a long time. I always test this - I set the gun where I think it's right then I put my hand over the wet spot and wait - if it's a nice warm breeze but causes no discomfort after one minute or so then I know it's not too hot.

These little heat guns are effective but take quite a bit of electricity, so if you're doing it in an old or poorly maintained house or in any situation where the wiring is at all iffy be sure to have a flashlight and know where the breaker or fuse box is ahead of time. On a number of occasions I've turned on my gun and immediately a breaker was thrown or a fuse blown. And be careful after you're finished with the drying and turn the heat gun off. ALWAYS unplug it (mine has a hair trigger) then put it somewhere pets and kids can't get it and let it cool for at least 20 minutes. You should see my burn scars. Great tool if used carefully and properly.

Here's something VERY important that I only found out recently - bleach solution should not be considered effective for more than ten days in its container after you mix it. I have various moisture problems as well as a number of household things I use a shot of bleach for on a regular basis. Until a loved one was dying recently and the hospice crew left literature for us to read I thought that the bleach solution was pretty much something that could sit in my sprayer for an indefinite period of time. According to that medical literature such is not the case. So given the importance of getting rid of mildew please keep that in mind. Ten days, wow.

Also, I have heard on more than one occasion that the Clorox brand is superior in some way to off-brands, and am not even positive that it's true, but given the importance of each of the things I use bleach for I consider it well worth the extra cost.

I hope that somewhere in all these side details you got something helpful, and I hope that you get all your answers very soon.

Good luck!
Mary