Wet basement: working out what kind of wet
“Wet” covers three different things: damp air that condenses on cold surfaces, moisture that seeps through masonry, and liquid water on the floor. Each has its own fix, and sometimes the inexpensive one is the right one.
You will be put through to an independent local waterproofing company. Calls may be recorded.
Three checks that take no tools
The plastic test
Tape a square of clear plastic tightly to a bare patch of wall and leave it for two days. Droplets on the room side mean the air is the source. Damp behind the plastic means moisture is coming through the wall.
The rain walk
Walk round the house in a steady rain. Look for gutters spilling over, downspouts ending at the wall, and ground or paving that slopes toward the foundation.
The calendar
Keep a note of the damp days for a month. Sticky August afternoons point to condensation. The day after a storm points to seepage. Early spring, as the ground thaws, points to a high water table.
Damp air
In a New Jersey summer, warm outdoor air carries a lot of moisture. When it meets basement walls and cold water pipes it leaves that moisture on them. Opening the basement windows in July lets more of it in.
The cure is to keep the windows shut and dry the air. A dehumidifier sized for the room, piped to a sink or a pump so that no one has to empty a bucket, usually settles it. Foam sleeves on the cold pipes stop the dripping.
Seepage through the walls
Seepage leaves evidence: white mineral powder on block or concrete, paint lifting in blisters low on the wall, a dark tide mark. The wall is passing moisture from wet soil even though no water runs across the floor.
The first move is outdoors, getting roof and surface water away from the wall. Where that is not enough, a wall liner over an interior drain takes the moisture out of the room.
Water on the floor
Liquid water after rain is past the point where drying the air will help. If it comes from one place, read basement leak repair. If it shows along a wall or in the middle of the floor, the house needs drainage and a pump.
If the water is there today, clearing it and drying the room is a water damage company's job; waterproofing comes afterwards.
Before you finish the basement
Carpet, stud walls and wallboard hide moisture until they smell of it. If you are planning a finished room, sort out the water first and then live with the bare basement through one wet season. A dry spring is cheap proof.
A musty smell means something is staying damp. Mould on bare masonry can be scrubbed off. Mould in wallboard or framing generally means that material comes out, and that is a separate trade. A waterproofing company's part is to remove the cause.
Wet basement questions
Is a dehumidifier enough?
For condensation, yes. For seepage it helps the room feel drier while the wall goes on passing moisture. For water on the floor it does nothing useful.
Why is it worse in summer when it rains less?
Because summer dampness is mostly from the air, not the ground. The plastic test above will confirm it.
Do I need someone to visit for a damp smell?
Do the three checks first. If they point to the air, try a dehumidifier for a few weeks. If the walls are the source, or you cannot tell, that is the time to have a company look.