It is difficult to finish your basement without eliminating or at least reducing the moisture. Moist basements might be acceptable for storage or for laundry rooms, but rarely for habitation. Carpeting and fibrous materials like curtains and bedspreads will develop mold. Hard surfaces like tile and painted drywall are easier to clean, but this kind of heavy cleaning becomes a regular feature of your life. It's better to identify the sources of the basement moisture and mitigate them, as best as you can.
Sources of Basement Moisture
Flood events are the most visible and dramatic type of basement moisture. While water may seep into your basement from the ground surrounding the basement walls and even under the basement floor, there are other sources of basement moisture that can be equally damaging.
Exterior Basement Flooding
Basement flooding can occur during larger, regional flooding events, inundating your home and others in the area. But it is just as common for homes to experience their own flood events. Poorly graded soil may send water toward the foundation, rather than away from it. Blocked gutters in a heavy rain will send vast amounts of water into the basement through cracks, windows, and doors.
Interior Basement Flooding
Basement flooding can come from inside, too. A broken pipe in the basement when an owner is away for a few days can be especially devastating. Water heaters can fail and washers can overflow. Blocked showers and bathtubs from upper floors can send water downward, where the basement collects it like a basin.
Condensation forms on basement walls: invisible, airborne water droplets that condense on cold surfaces. Since basements tend toward the cooler side, condensation will naturally form.
Keeping the temperature point high enough to ward off condensation is a good tactic when combined with other methods like running a dehumidifier and blocking water access from the exterior. Basements in some areas run dehumidifiers constantly to pull the moisture from the air before it lands on walls and floors.
Groundwater is water that seeps through the porous spaces in the soil and rocks from rain, snow melt, melted ice, irrigation, and stormwater. Most ground has groundwater.
Sump pumps are a regular feature of many basements. Having a sump pump often doesn't mean that your basement is seriously flawed; it simply means that you have a basement. Sump pumps help combat groundwater that threatens your basement from below. Sump pumps are always on. When water in the sump (hole) reaches a certain level, the sump pump will turn on and vacate that water.
How and Where to Locate Basement Moisture
The most obvious sign of basement moisture is standing water. But beyond that, learn to look at your basement like a detective and search for other signals such as degrading materials and rust.
- Peeling paint on the walls (condensation will cause the paint to peel)
- White, powdery material on brick walls called efflorescence
- Rotting wood
- Flaking drywall
- Rusting water heater, dryer, washer, or other appliance platforms or feet
How to Fix Basement Moisture
Eliminating or mitigating moisture in your basement is usually not a step-by-step process but one of employing a toolkit of targeted measures that will attack most, if not all, of the issues. Generally, you will want to begin outside of the home before you work indoors.
Regrade soil around foundation walls to prevent water from moving toward the foundation. With a shovel, bank up the soil to the masonry foundation wall, then slope that earth down and away from the house.
Redirect Downspouts and Extensions
Direct downspouts far away from the foundation and basement walls. Add downspout extensions to carry the water away from the foundation.
Clean the Gutters
Clean gutters to prevent overflowing gutters from flowing next to the foundation wall.
Fill Large Cracks in Foundation Walls
Use a product like a hydraulic water-stop compound to fill large foundation holes and cracks. Silicone caulk is not adequate for filling these cracks.
Seal Outside of the Foundation Wall
Trowel about 1/4-inch of surface bonding cement using a straight-edged trowel. Wait three hours for the cement to dry. Scribe lines in the bonding cement with a scribing tool or paintbrush cleaner to help the second coat better adhere to the surface. Apply a second coat of the bonding cement. Wait three to four days for all coats to fully dry.
Apply a Masonry Waterproofer
Roll and brush on a waterproofing masonry sealer on the inside of the basement, on exposed concrete or masonry walls.
Install a Sump Pump
To keep groundwater in check, install a sump pump. Installing a sump pump is a major undertaking, requiring the services of a contractor and a licensed electrician.
Your basement floor must be broken up and later re-patched, and plumbing and electrical wiring are also involved. After installation, the sump pump is on-guard 24 hours a day, every day (though it is not running continuously). When the water level in the sump reaches a prescribed point, the pump will turn on and expel the water.
When to Call a Professional
Basement moisture is one of those bedeviling problems that might seem impossible to fix. Once you have fixed one source of moisture, another source appears. But there are reliable methods of drying out your basement or at least creating a more dry basement than you already have.
Professionals can help you find the sources of the basement moisture and eliminate them. Look for basement waterproofing experts or call a general contractor who has experience with basement moisture mitigation.
Moisture in basements: causes and solutions. University of Minnesota Extension
Groundwater. State of Washington Department of Ecology