Relative Humidity

[musicman2000]

I live in Baltimore, Maryland. The summers here are pretty hot, and the RH in my basement (where my work area is) hovers right around 55%, and spikes right around 59%. I am about to start my first build. I am told that the ideal RH is 40 - 50%. Should I have cause for concern? Unfortunately I sold my dehumidifyer 2 years ago.

Tom

[B. Howard]

Building at too high of an RH can lead to cracks in dryer times. 55% is marginal at best, 60% is too high.

[tippie53]

A dehumidifier should be used. RH control is one of the most important things to control for the best result. I like 40 for gluing up bracing.

[Tom West]

The range of 35 to 40 RH is the area I like to use for building. There is a strange paradox, while building, too high RH will most likely get you into trouble compared to too low RH. When the guitar is finished too low RH will most likely get you into trouble compared to too high. The moral is, have the building and living RHs as close as possible to have the least stress on the guitar. The 40-45 range seems to be the accepted norm.
Tom

[musicman2000]

Ok, here is the deal:

I actually bought one of those mini dehumidifiers for $50. I thought it would save me some money and be enough to reduce the humidity in my small 8 X 6 work area. Unfortunately, my work area happens to be in the basement.

After running it for 3 days, I am no longer going over 55% RH, but I still can't get it to go below 50%. I was hoping this little unit would get me a little closer to acceptable levels in this very humid Maryland climate.

I traveled to Martin in Nazareth, PA yesterday to pick up the guitar kit (laminate rosewood OM). It has been sitting in my basement in the box unpacked. I have the guitar mold. Should I rush out and get a more conventional dehumidifier right away? How long can I let it sit at 50% before I have some problems? Should I get the sides into the mold? Time is of the essence here so any help you can offer would be appreciated. I'm still not happy about the fact that I now have to invest another $200. But if that is what comes with the territory, I'll do it.

Tom

[mjmeehan]

Hi Tom.
I'm a basement builder as well. I use a larger style dehumidifier it runs all the time and drains directly to the sump pump. It's a very large, concrete basement, so I'm not surprised. I'm able to keep the humidity at about 40-45% and have not had a problem (never had much of a problem at 50% either). But a larger dehumidifier may be in order for you. It will be worth it when the wood stops doing weird things as a result!
And yes, get the sides into the mold. That should help in the mean time.

Mike.

[SKBarbour]

I have a model that I bought from Sears. I have it set to cycle on and off. Seems to work fine, if I let I run constantly the humidity drops too low. I usually keep it between 45-50%. It's not precise enough to hold right at a specific rh, so I just keep a closer eye on more critical parts of the process.

[ruby@magpage.com]

Tom
Controlling RH can be a complex problem. First, basements are always a little higher than the rest of the house in RH because they are a few degrees cooler and Relative Humidity is, well, relative, and it is relative to temperature. The lower the temp goes, the higher the RH in the same air goes, and if there are air conditioning outlets in the basement, the temp can be a few degrees cooler yet. Second, the basement can get moisture from the ground around the walls as it readily passes through the concrete or block. Third problem is that if the house has a high air leakage rate, outside humid air can get in and raise the RH of the whole house. And fourth, most air conditioners in your (our) area are oversized meaning they do not do enough basic dehumidification to begin with because they don't run long enough.

So the amount of moisture in the air will be higher for a house in a humid climate with a cool, wet basement, a high leakage rate, and an oversized air conditioner, than the same house with a warmer, dry basement, low leakage rate, and slightly undersized air conditioner.

At any rate, a big enough dehumidifier(s) will overcome all of these problems - I might leave the one you have run for a full 2-3 weeks for the initial drying, then maybe it can keep up. If not, you can rent one temporarily to help out - or you could fix any of the above problems, some being more expensive than others.

And when buying a dehumidifier, get the biggest one you can - 50 pints or more - because they are expensive to run and the bigger ones are more efficient.

Good luck
Ed Minch
Chestertown, MD

[musicman2000]

Thank you all for the advice. I bit the bullet and bought a dehumidifier today. I got a 50-pint Kenmore from Sears - I have heard good things about their longevity and quietness, and I sprung for the extended warranty. I think it was worth it. I am quickly finding out how much money it takes to get this "hobby" up and running.

Ed, I live in Baltimore if you ever want to collaborate. Thanks for the advice

Tom

[ruby@magpage.com]

Tom

I would love to. My business has an office in Pasadena. I am on guitar #3 and loving it. My PM is ruby@magpage.com