Basement Humidity control

[Bob Johnson2]

The recent basement shop thread got me wondering what you other bottom dwellers do for humidity control. I've been running a dehumifier for the last 20 years and am going to get a 2nd one tomorrow as my shop has grown. When talking to a coworker yesterday he mentioned that he is in the midst of painting all his concrete, the walls with Dry-Lock and the floor with epoxy paint of some sort, figuring the majority of the dampness comes through the concrete. Has anyone tried this? I do notice that without the DH's running the floor gets a damp look to it. Summers the bad time for me as the furnace doesn't run much.

[Tyler Howell]

Bob,

I run a 20" window fan 24/7 in summer and about 1/8 of the time in winter. The dehumidifier runs only once in a while on bad days. The fan is cheaper to run and with a 20" furnace filter over the input keeps the air a little cleaner;)

[JayStPeter]

I actually have heat/ac vents down there. Keeps it pretty nice. I keep the vent in my shop closed off (and packed with insulation) to avoid dust and noise.
Every so often, the drain in my outside stairway clogs and I get some water penetration. I dehumidify with a shopvac when that happens :D
I'm learning to keep the stairway clean :cool:

Jay

[Carl Eyman]

I don't have a phsycometric chart here at home. Not even sure I'm spelling it right, but if I did I could give you an example of why my Wisconsin basement was humid. For example think of a typical hot summer day. Maybe dry bulb temp is 85 and wet bulb about 75 to 80. That air got into the basement where the ground temperature under the floor was maybe 55. What happened? Moisture condensed out of the air and deposit itself on the floor, walls too, probably. The air in the basement rose in relative humidity to 100%. The cheapest way to dehumidify it is to heat it up to or beyond the wet bulb temperature. But who wants to get sent to the booby hatch for running a heater when the temperature is 85? The RH will drop after you reach the WB temp and moisture will stop condensing on tools. I had a dehumidifier, but it was way too small for the job; so my tools got rusty.

[Bob Johnson2]

I don't have a phsycometric chart here at home. Not even sure I'm spelling it right, but if I did I could give you an example of why my Wisconsin basement was humid. For example think of a typical hot summer day. Maybe dry bulb temp is 85 and wet bulb about 75 to 80. That air got into the basement where the ground temperature under the floor was maybe 55. What happened? Moisture condensed out of the air and deposit itself on the floor, walls too, probably. The air in the basement rose in relative humidity to 100%. The cheapest way to dehumidify it is to heat it up to or beyond the wet bulb temperature. But who wants to get sent to the booby hatch for running a heater when the temperature is 85? The RH will drop after you reach the WB temp and moisture will stop condensing on tools. I had a dehumidifier, but it was way too small for the job; so my tools got rusty.

So your aying that the patchy damp look is caused by the humidity in the air as opposed to slowly seeping through the cement. Makes sense as I'd figure the ground is dryer in the summer (as evidenced by the sump being bone dry) so paint would probably do little if anything to cut down on the humidity. With a lone 10' of electric heater for 1800 sq' I guess getting it to 85 degrees is out too. Guess I'll buy that 2nd dehumidifier tomorrow or see what I can find for a basement window fan like Tyler uses. Running 2 dehumidifiers will probably cost about the same as heating it to 85!

[Dave Anderson NH]

I have had a basement shop for 16 years in my current house. It was relatively damp (but not wet) in the early years and I took several steps to solve the problem. With forced hot water baseboard heat in the house I insulated all of the hot and cold water pipes with the foam sleeves and did the lines to the baseboard too. This eliminated drips from sweating in the summer. Next I painted all of the concrete walls with the UGL Drylok paint, 2 coats. Do yourself a favor if you do this, buy the latex based stuff. When I bought the first 2 gallons they were the oil based version. I started applying them at nite after Sue and the dog went to bed. I was just opening the second gallon when they both came tearing down the stairs to the basement from the second floor bedroom complaining, "What's that smell?" The stuff is really strong and obnoxious. I completed the job with the latex which has almost no odor. Finally I got for Christmas one year a 2 station Radio Shack battery operated temp and humidity moniter. I moniter it carefully and try to keep the relative humidity around 40% most of the year. This is done with a dehumidifier which usually runs from about May 1st until the end of October.

[John Hart]

Carl is absolutely right. Dampness on surfaces is due to moisture coming out of the air. This is what dewpoint is all about. You can use this chart below (if it posts correctly). If your air temp is 75 degrees and your humidity is 60% then moisture will condense on surfaces that are 60 degrees and below. Walls and floor of a basement will be at ground temperature so that's what you're dealing with. The mats I've covered my floor with, have resolved the "wet floor" problem because it's surface is the same as the air temperature. I drywalled my cinderblock walls, so that solved the "wet wall" problem. As long as my tools are the same temperature as the shop, they don't collect any moisture either.

60-70% humidity is ideal for humans. Maintain your temperature so that you don't reach a dew point.

<TABLE height=488 cellSpacing=0 width="97%" border=1><TBODY><TR><TD vAlign=center borderColor=#000000 width="6%" height=59 rowSpan=2><DL>
<DT>Air Temp </DT>
<DT>ºF </DT>
</DL></TD><TD borderColor=#ffffff width="94%" colSpan=19 height=31>
<BIG>% Relative Humidity</BIG>

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[Bob Johnson2]

Thanks John, I'll pick up a meter for the humidity (which is easier said then found) and do some experimenting to get the hang of the chart.

[Tom Pritchard]

Thanks John, I'll pick up a meter for the humidity (which is easier said then found) and do some experimenting to get the hang of the chart.

John, Radio Shack has some inexpensive digital thermometers that read relative humidity as well. They are fairly accurate, and under $30.00 if I remember correctly.

Here's a link to the one I was looking at. You may catch it at a lower price at your local store, or they may have one without the barometer that is cheaper. Here's the link:

Radio Shack temp/humidity/barometer sensor (http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F010%5F005%5F001%5F000&product%5Fid=63%2D1086)