Newbie Question - Humid Basement

[Eric Garner]

Ok, I am in the process of converting my basement into a workshop, but I am having humidity problems. My basement has cinder block walls and two garage doors. I have a dehumidifier running non-stop and just got finished using UGL Drylok to seal the walls.

I can program my dehumidifier to shut off at a desired humidity level. After dryloking the walls I can get it to shut off @ 65%, but it continues to run nonstop @ 60%. Do I need to seal the concrete floor with epoxy paint?

My goal is to get it down to at least 55% humidity. From your experience is this possible?

Thanks!

[Gary Keedwell]

Sounds like you are where I was 3 years ago. I bought some stuff at the BORG and sealed my floor. Alot of cleaning first. ( or etching). I then painted my floor a nice tan color. It has held up real good.
Mu dehumidifier runs alot in the summer but that is the nature of the beast. I have a pellet stove that keeps me toasty in the winter.:)
How old is your basement floor? If it is real old you might have to etch the cement first. My friend painted his floor without a thorough cleaning and it started peeling almost immediately.:(
Good Luck
Gary K.

[Eric Garner]

The house was built in 1982. I will definitely etch it and clean it thoroughly. We just bought the house and the previous owner didn't keep a very clean basement. Lots of paint stains, rust stains, etc...

So, it sounds like sealing the floor is a must. I just didn't want to spend the time and money without seeing an improvement.

[Eddie Darby]

I would consider the outside of your building as well. Eaves trough, with long bottom shoots, that funnel the rain water well away from the foundations, and sloped land for drainage will keep the rain water away from the house, and make things better.

I know someone that has their rain water run off the roof, and under the driveway, to an underground rain barrel to then be released into the soil well away from the house.

New houses now are being built with a black plastic external water barrier on the outside of the basement walls.

I've also built what we call at the golf course French Drains, that provide drainage pretty cheaply. They are just sloped troughs under the ground, filled with gravel, and covered with landscaping fabric to screen the fine soil particles out from clogging the drain, then topped with soil and grass.

[Josiah Bartlett]

French drains work really well as long as you give them somewhere to drain to.

Make sure that whatever you do, you do it evenly around the entire perimeter of the foundation, especially if you have high clay soil content.

The previous owner of my house had put in a paver patio and re-routed all the downspouts on one side away from the house, and left the other side bare dirt with close downspouts. Now one side of my house is 1" lower than the other, because the wet side expands and contracts seasonally more than the other. I'm in the process of correcting that problem.

[Cliff Rohrabacher]

You took a different route than I. Sealing my cellar is not an option. The original hole was dug 250 years ago.
The site is wet - I mean the water table is about 50 or so feet above the roofline maybe the chimneys.

I got two April Aire whole house units and parked one in the Cellar and one in the attached garage shop. They took me from having a monsoon season to about 50-46% RH most all the time.

They really made a difference. It used to be so bad that exposed steel had to be oiled or it would rust.

If you buy an April Aire get it online. My HVAC guy wanted $4000 for one. I got the units for under $2-Gees each.

[Dave Malen]

Eric,
I have a house that is 20 years old with cinder block walls (painted with drylock) in the basement. Recently I bought a delonghi dehumidifier (55 pints per day,low temperature,internal pump) to bring down the humidity level. My basement shop is about 1000 square feet. Initially the humidity was 70%. The dehumidifier has been running constantly for the last 4 days and has brought the humidity down to 54%. I set it for 45% but it seems to be stuck at 54%

Dave

[Gary Keedwell]

Eric,
I have a house that is 20 years old with cinder block walls in the basement. Recently I bought a delonghi dehumidifier to bring down the humidity level. My basement shop is about 1000 square feet. Initially the humidity was 70%. The dehumidifier has been running constantly for the last 4 days and has brought the humidity down to 54%. I set it for 45% but it seems to be stuck at 54%

DaveYour probably lucky to get it down that much. With your footage, it might be a job for two dehumidifiers.:( :)

Gary

[Dave Malen]

Your right. Now all I need is another $300 for another one. Plus a loan for my next electric bill :)

Dave

[Gary Keedwell]

Dave,

LOL I know what you mean. My neighbor used one for ONE season and couldn't believe the electricity bill. She hasn't used it since.:)
Gary

[Chris McGowan]

Dave,

LOL I know what you mean. My neighbor used one for ONE season and couldn't believe the electricity bill. She hasn't used it since.:)
Gary

I have a 55 pint Goldstar that even being the new Energy Star model still takes alot of juice. Fan only on low about 30 watts, fan on low with compressor about 420 watts. I keep the unit at 55% year round (block walls, not sealed yet). During the summer it runs almost all the time and adds about $26 a month to the electric bill. During the winter it runs maybe a total of about 8 hours cycling through the day.

Hopefully when I get around to it, I have 2 50 lb bags of Throuseal to mixup and brush on the walls. Getting to it is the key word... the bags have been in the basement for 5 years now :D

[Eric Garner]

So, does anyone know how much moisture comes up through the slab? Sealing the cinder blocks was a no-brainer for me. I could see and feel the dampness in the blocks after it rained, but I'm still not sold on sealing the floor. Should I just bite the bullet and do it?

[Gary Keedwell]

I sealed my neighbors floor but not her poured concrete walls and it doesn't smell like a basement like it did before. I also think it is alot cleaner with the floor sealed. IMNSHO.

Gary

[jason lambert]

I dry locked the walls, French drains then put plastic up and built a walls. Worked good that was stage one. Stage tow was I was going to seal the floor tried it but the floor sealer would ware out and make a little difference in humidity what I finally wound up doing is putting down good linoleum tiles. It seals the floor by covering it and is much cleaner and easer to roll stuff on and for what I do will never ware out or ware through like the sealer.

[Greg Sznajdruk]

Relative humidity is the ratio of the amount of water vapour in the air at a specific temperature to the maximum amount that the air could hold at that temperature, expressed as a percentage.

Relative humidity is a meaningless number since it does not indicate the amount of water vapour in the air. So adjusting the humidistat to 45% is only meaningful if the temperature is constant, you will still get a varriation of Relative humidity. If the temperature varies the 45% doesn’t mean that there is 45% of the air comprised of water vapour.

What you need to know is what the specific humidity is in your shop. Specific humidity can be calculated using the Relative humidity and the temperature. Specific humidity can be calculated using Psychometric charts you will then come into the world of Thermodynamics.

There are a number of sites that have an on line calculator which will give you the Grains Per Pound (GPP).

In a wood shop with cast steel surface what is really need to know is the Dew Point. The Dew point is the temperature at which the water vapour will condense. The cold drink in the summer time when water vapour condenses on the out side of the glass, since the temperature of the glass is below the dew point.

For example if the temperature is 60 degrees F and the rh is 60% the dew point is 46 degrees F. If the temperature does no fall to 46 degrees there will be no condensation.
Greg

[Gary Keedwell]

I dry locked the walls, French drains then put plastic up and built a walls. Worked good that was stage one. Stage tow was I was going to seal the floor tried it but the floor sealer would ware out and make a little difference in humidity what I finally wound up doing is putting down good linoleum tiles. It seals the floor by covering it and is much cleaner and easer to roll stuff on and for what I do will never ware out or ware through like the sealer.
After I sealed my basement floor..I painted it with paint formulated for floors. I have done this to two basements with real good luck. The paint protectect the sealer. Using a roller with a long handle...the paint went down extremely fast.
Gary

[Eric Garner]

Relative humidity is the ratio of the amount of water vapour in the air at a specific temperature to the maximum amount that the air could hold at that temperature, expressed as a percentage.

Relative humidity is a meaningless number since it does not indicate the amount of water vapour in the air. So adjusting the humidistat to 45% is only meaningful if the temperature is constant, you will still get a varriation of Relative humidity. If the temperature varies the 45% doesn’t mean that there is 45% of the air comprised of water vapour.

What you need to know is what the specific humidity is in your shop. Specific humidity can be calculated using the Relative humidity and the temperature. Specific humidity can be calculated using Psychometric charts you will then come into the world of Thermodynamics.

There are a number of sites that have an on line calculator which will give you the Grains Per Pound (GPP).

In a wood shop with cast steel surface what is really need to know is the Dew Point. The Dew point is the temperature at which the water vapour will condense. The cold drink in the summer time when water vapour condenses on the out side of the glass, since the temperature of the glass is below the dew point.

For example if the temperature is 60 degrees F and the rh is 60% the dew point is 46 degrees F. If the temperature does no fall to 46 degrees there will be no condensation.
Greg


Thanks Greg. I can see how the Dew Point is important for the cast iron tops. Does the same apply to wood? I found the following conversion chart. Assuming that I never want a MC in my wood higher than 12% does that mean that the RC in my basement should never be > 65%? As you mentioned RC is based on Temp. So, I would also need a pretty constant temp in my basement too.



http://www.woodweb.com/knowledge_base/Ratios_Relative_humidity_to_moisture_content.html

A hygrometer measures humidity. A thermo-hygrometer measures humidity and temperature. A psychrometer has two thermometers (one wet and the other dry) that measures temperatures and can be used to calculate humidity. The property of the air is called the equilibrium moisture content (EMC) and it is numerically equal to the MC that wood will achieve during drying if you wait long enough and if the conditions do not change. (Example: At 30% RH, wood will achieve 6% MC. So the air has an EMC of 6%.)
Common conversions:
0% RH = 0% MC = 0% EMC
30% = 6%
50% = 9%
65% = 12%
80% = 16%
99% = 28%

[Greg Sznajdruk]

Gary:

As far as wood goes you are right. The Equilibrium Moisture Content (EMC) is defined as the moisture content (MC) at which point the wood is neither gaining nor loosing moisture.

The chart you show is correct at 30 degrees F. The MC will vary with temperature however the range from 30 to 90 degrees is marginal difference. So in your case once the wood has reached EMC at a fixed RH the temperature can vary significantly in your shop with little affect to the MC.

Greg