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Old 06-23-2017, 09:28 AM   #1
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Cleaning before Painting Concrete block basement


Hello. I live in NJ and have a 10 year old home with concrete block foundation. Except for the few times when groundwater was high and water was pouring into the sump pit and getting pumped out, our basement has been dry. I have taped plastic to the walls and floors and left them on for an entire year, and no moisture has formed on the inside or outside of the plastic. My basement does however have a musty smell, which almost disappears if I run a dehumidifier. I will be installing an exterior door at bottom of our Bilco doors to seal the basement from outside air. I also am building a 240 cfm fan with ducting that runs from 4" above the floor to the outside. This was installed by a contractor friend of mine in his own home and worked great so I am doing to same to lower the relative humidity. I will also be painting the floors and walls with Drylok and Drylok floor paint respectively. I have wire brushed and vacuumed the walls and will be etching the walls to remove efflorescence where the Bilco doors used to leak and etching the floor where it seems a little too smooth to accept paint.
My question is as follows: My wife wants to clean the bare basement walls and floors with a bleach solution to kill any mold that might be present (musty smell). I am not opposed to this but my concern is that the concrete might not dry for a very long time. We are planning on painting in mid July. Any thoughts are greatly appreciated. Thanks so much!
C.
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Old 06-23-2017, 10:13 AM   #2
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Re: Cleaning before Painting Concrete block basement


A basement dew point temperature reading will give you an indication of how long it will take washed walls to dry. A wet towel suspended in the basement from the spin cycle of a load of laundry will also give you a drying time estimate. Should dry over night.

The plastic test only tells you the concrete surface has never reached the dew point temperature for the air mas people believe they hermetically sealed under the plastic.

A better test is to put an oatmeal cookie in the basement for 2-3 days to determine air moisture content. Good = crispy, snaps when bent. Questionable moisture = bends a little before breaking. Poor = can make nearly a 180 bend and it never really snaps. It's still good to eat and you'll get a general idea of your basement air's moisture content.
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Old 06-23-2017, 10:30 AM   #3
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Re: Cleaning before Painting Concrete block basement


Welcome to the forum.
NJ humidity is on the high side so blowing basement air out is just requiring outside air to come back in somewhere. That somewhere is often between the house and foundation, lots of small leaks.

There are different opinions on minimizing moisture levels in the basement and trying to seal them with drylock is not the best. Check its specifications as I believe it is intended to block water and not moisture vapor. Moisture vapor is the more common and very difficult to stop. But it is slow so a dehumidifier should be able to control the humidity down there.

The reality is, a dry basement starts with location, landscaping, and waterproofing methods from the outside but the added cost is unattractive to buyers so NOT dome on any homes unless specifically desired. Your description says it was not done with yours, you join the 99.9% of home owners.

I'll add a link in case you haven't found it but it may shed some light on the task you face.

Formerly from Middletown and Brick so I understand NJ humidity, yuck.

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Old 06-23-2017, 12:14 PM   #4
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Re: Cleaning before Painting Concrete block basement


Nothing wrong with using bleach to clean [I use it a lot] BUT the bleach needs to rinsed well. Most any cleaner residue can affect how well a coating will adhere.
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Old 06-23-2017, 02:55 PM   #5
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Re: Cleaning before Painting Concrete block basement


Quote:
I will also be painting the floors and walls with Drylok and Drylok floor paint respectively.
Waste of time and money, IMO. If you have a water problem, it needs to be addressed from the outside with gutters, downspout extensions and grading. Sounds like this is not generally your issue, though. Vapor, on the other hand, is common in a basement and a good dehumidifier and air circulation is the answer.
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Old 06-23-2017, 05:12 PM   #6
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Re: Cleaning before Painting Concrete block basement


Not a terrible fan of bleach, it is toxic and smells bad. I prefer to put a pray top on a peroxide bottle to kill mold. Not sure either can kill all mold. To each his own.
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Old 06-23-2017, 07:16 PM   #7
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Re: Cleaning before Painting Concrete block basement


Hi everyone! Thank you so much for all of your replies! I truly appreciate that! Some of you have said that spraying bleach on the mold is okay but I don't actually see any. There's just the general musty smell, and some of the items are musty. I am concerned that using anything on the walls that leaves a residue would have the potential to cause the paint the fail if I don't get it all off. Do you think that wire brushing the walls and vacuuming is just as good as chemicals on 10 year old block that looks and feels pretty clean already?
Thanks!
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Old 06-24-2017, 06:38 AM   #8
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Re: Cleaning before Painting Concrete block basement


Ideally you'd pressure wash a week or so before the painting but that doesn't work well in a basement. Is there effervescence on the walls? I usually just wire brush it down and then apply the drylok. I assume the foundation wall is unpainted as drylok isn't formulated to be applied over paint.

Running a dehumidifier along with air circulation will do the most good towards getting rid of the musty odor!
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Old 06-24-2017, 11:02 AM   #9
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Re: Cleaning before Painting Concrete block basement


Yes the block is not painted. One post has mentioned that there are many air leaks between the basement foundation and the sill plate, windows etc where humid air can come in. I am thinking that may not be the case here since this home was built to energy star specs and passed with flying colors but maybe the basement wasn't included in that calculation? I know for sure that I can see light from the Bilco doors so hopefully by installing an exterior door at the bottom of the stairs a lot of that moist air will be eliminated and by installing the axial fan to blow the basement air outside, air from upstairs inside will be drawn into the basement as dry replacement air. Wishful thinking?

Last edited by oldssupreme; 06-24-2017 at 11:05 AM.
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Old 06-24-2017, 11:24 AM   #10
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Re: Cleaning before Painting Concrete block basement


If you have a very tight home then you would also have a mechanical ventilation system, HRV or ERV, or an exhaust fan programmed to generate the required ventilation (leakage). The threshold for needing mechanical ventilation is a complete air exchange every 3 hours. So no mechanical ventilation and your house is exchanging at that rate on average. If you are tighter without powered ventilation then windows will fog up in the winter and humidity will be high.

Meeting Energy Star requirements doesn't automatically mean a sealed home, and the house to foundation and rim band would still be a source of incoming air.

I'll add a link that calculates dew point where you can compare inside and outside air with house or basement. It helps to determine the contribution from outside.

Bud
http://andrew.rsmas.miami.edu/bmcnoldy/Humidity.html
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Old 06-24-2017, 11:41 AM   #11
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Re: Cleaning before Painting Concrete block basement


Thank you Bud much appreciated. We do have an exhaust fan in one of our bathrooms that we were required to put on a daily timer. We have the 70cfm fan on for 45 minutes per day and we don't have any issues with windows fogging up in the winter. We also run our other two bathroom fans which are 70 and 110 Cfm for about an hour or more each during and after our showers. I'll check out your link. Thank you!
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Old 06-24-2017, 11:44 AM   #12
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Re: Cleaning before Painting Concrete block basement


I have also noticed that in the summer on humid days if I don't have the dehumidifier on in the basement, the water pipes from the well have condensate as well as the well
tank. If it is running, condensation is little or non existent.
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Old 06-24-2017, 12:50 PM   #13
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Re: Cleaning before Painting Concrete block basement


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Originally Posted by oldssupreme View Post
I have also noticed that in the summer on humid days if I don't have the dehumidifier on in the basement, the water pipes from the well have condensate as well as the well
tank. If it is running, condensation is little or non existent.
Chris
The well water is checking dew point temperature for you, and the D P is that water temp. or above. To ever rid the basement of a musty odor the dew point will need to be down in the 40 range with a room temperature of about 72. That 40 degrees D P can usually be easily check with a container taken from the refrigerator which is often recommended to be around 40.
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