Condensation on basement glass block windows

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Old 11-10-18, 03:06 PM
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Condensation on basement glass block windows

Hi - I have several glass block windows in my basement, and a few of them constantly seem to have condensation on them whenever the temperature drops below 40 outside. The ones with the worse condensation all have an angle iron just above the glass block.

I have filled any visible cracks in the mortar using concrete caulking, and then applied two coats of Drylok to reseal all the mortar around the windows, both inside and out. I have a low temperature dehumidifier running in the basement, and it’s always been dry with normal humidity.

My problem is the condensation forms all around the windows (see photo’s attached), and if not wiped down occasionally, begins to mold.

Can anyone suggest a way for me to stop (or minimize) this problem?

Thank you and appreciate any suggestions/help!!
Denny
 
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Old 11-10-18, 03:30 PM
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Glass is a horrible insulator, as is steel. So what you are seeing is pretty normal, and you are likely already doing what you can to limit the problem.

Glass blocks are old technology and its well known here that I'm not a fan of them. Science backs me up. The r-value of a standard glass block is under R-2, which means the u-factor is about .51. Typically, for a new window to qualify for an "Energy Star" rating nowadays, it needs to have a u-factor of .33 or higher. (a number that is closer to 0 is better)... and even a crummy vinyl window with triple pane low-e glass can blow that out of the water, getting closer to .20. Its not a huge difference, but it explains why I would recommend better windows as a means to help reduce the likelihood of condensation. I'm sure there are some sort of glass blocks (more than likely they would be acrylic... not glass) that would qualify as being energy efficient, so its not like I am totally against them. Just against the standard ones from 1950. LOL

Other things that might help:

Turn the humidifier down ever farther so that it runs constantly... or get a larger humidifier that can pull more moisture out of the air per hour. Many larger ones will have their own bilge pump, which is nice because then it can run constantly without ever needing to be emptied. Basements are a never ending source of humidity, so let it run. Also the readings on the floor where the humidifier is likely sitting do not accurately represent the humidity near the ceiling, where warmer air is. So let it run.

Turn on a fan to circulate air. Your glass block windows are recessed deep in the wall, and that removes them from the heat source, so they get colder than they would if the wall was, say, only 5" thick. If you stick your hand out there you can likely feel the difference in temperature. By running a fan you can circulate more warm air into that recessed area which might help the glass stay a little warmer and dryer.

Clean the glass often, using a mold fighting detergent / cleanser. Something like "Tilex mold & mildew" would be a good choice. Or "Soft Scrub mold & mildew with bleach".

Use only paints and caulkings that have built in mildewcides.
 
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Old 11-10-18, 06:39 PM
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Thanks, this is very helpful!
 
 

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