Mold and Moisture
Molds are microscopic fungi that live on plant and vegetable matter. They can be found almost anywhere, they grow on virtually any surface where moisture is present.
Molds reproduce by tiny microscopic seeds called spores, they are in the air all the time, an air filter can capture some but not all of them. To eliminate them all you would have to use clean-room technology, complete with airlock, shower, and full body white suits. Spores come in when you open a door or window, there is no practical way to eliminate them in a normal house, and there is always plenty for them to feed on. They will grow on carpet, they will grow on drywall, they will grow on paint. You will not eliminate their food.
Think then of mold resting on a three legged stool made of
Cut one leg and the stool falls over. By far the easiest one to cut is moisture.
To cut moisture there are three rules:
1. You can not eliminate all moisture. If you did, you could not live in the house or work in the office. It would be too uncomfortable. Fortunately, at levels of moisture that are practical to attain and comfortable for people, mold can not grow. It may still be alive, hibernating, waiting for that flood or leak, but it won't grow.
2. Work for 50% relative humidity, plus or minus 5%. Get a hygrometer to monitor the humidity level. When you consider the cost of mold remediation, the cost of a hygrometer, starting at under $20 at most hardware stores, to prevent mold in the first place is a good deal. If your house stays naturally in the 50% range, great. If you have to, get a dehumidifier and set it on 40 to 45%, just to be on the safe side. Most dehumidifiers are set centrally in a room, so at a far wall humidity will be higher.
3. Low overall humidity will not help if your house still has leaks or high humidity problem areas. Find and fix your leaks. Look at your basement, attic, washing machine, dishwasher, sink, bathroom, and if you have exhaust fans in the kitchen or bathroom, use them when cooking or showering. Make sure your cold water pipes do not drip condensed water, you may have to insulate them. Make sure your kitchen and bathroom walls and windows do not have condensing water running down them when cooking or showering.
So these are the rules: you can't get all the water, you wouldn't want to, just get half. Get a hygrometer and use it, and a dehumidifier if you have to. Find and eliminate the problem areas.
Although the center of the house may be dry, it is in the corners, nooks, and crannies, where air circulation is not as good, where the problems start. There the humidity may be much higher, that's where you can get the mold growth in an otherwise dry room. Good air circulation can be a great help.
Get the water away from the house. If you have gutters, clean them and put tailpipes on the downspouts. If you don't have gutters, make sure the water drains away form where the eaves drip. A house where water runs in a circle, from off the roof down to the ground, then right back under the foundation is a house looking for a mold problem.
If your roof leaks, fix it. Keep your roof clean and free of branches or leaves that can pile up and pool water. Get the water off the house in the first place, then drain it away.
Look carefully at your landscaping. Is it holding water next to the house, or will it allow circulation? Plants are wonderful, but they take water form the ground and send it out the leaves. It is how they survive. Cut back your plants so your house can breathe dry air.
If you can follow these simple, but sometimes costly or difficult, steps, your house should not grow mold. They won't help the mold that is already there, that mold has to be cleaned out. But at least once you get it cleaned out you will not be growing more. Cut the root and the plant dies. Mold does not have roots, it has to have the water brought to it to grow. Cut the water and the mold does not grow.
A couple of good websites with much more detailed information on these topics are: