You can fix a wet basement. It isn't easy, but it's possible. And if you have plans to finish off your basement to add useful living space in your home, you need your basement to become a dry basement before you spend money on finishes. And this is something you want to do right the first time. Halfway measures that fail later will end up costing you lots of money later.
If you have a basement that's damp or even has running water, chances are it wasn't built properly in the first place. I discuss how to do it right in my article about Building a Basement.
If you have a wet basement, you probably do not have the proper waterproofing on the exterior of the basement walls, there probably isn't a good footing drain or it's been clogged or crushed, and you probably have places where water can collect around your house walls.
Let me state here that "handling" the water that enters your basement and pumping it out is not really a solution. It does not fix the actual problem. It only deals with the symptom, not the illness.
The secret to a dry basement is to make sure the water never gets in, at all. Let's look at ways to cure the illness and not just the symptoms.
The most important and least costly steps you can take toward fixing a wet basement are to correct the slope of the ground around your house to make sure water is draining away from the basement walls and to clean, fix, or add gutters and downspouts.
It’s best to have the downspouts discharge the rainwater far from the house and not end on simple splash blocks. Any water that collects near your house will seep into the soil and eventually find its way into your basement. Water always finds a way.
The second step toward fixing a wet basement is to dig up the soil around your house, re-waterproof the basement walls, add drainage stone, and install drain piping. This is the sure method for resolving your wet basement problem. But it will be very expensive and messy. All this digging will force you to replace your landscaping, too.
However, if your wet basement problem is severe and you truly want to do the job right, this may be your only option. And if your builder left you with this problem, he or she has an obligation to fix the cause of the problem and make things the way they should have been from the start.
Once the soil has been dug away and the exterior of your basement walls is exposed, they must be power washed to remove all of the dirt. When the walls are clean, a high-grade waterproofing system such as Tuff-n-Dri should be applied. The traditional, paint-on black mastic that may even be on your walls already, is not good enough. It simply is not waterproof.
The best of the higher level waterproofing systems coats the wall with up to a 40 mil. asphalt emulsion that sets up to a rubbery consistency. Over that, a semi-rigid board of pressed fiberglass is installed. This board helps insulate the wall. But its more important function is that it acts as a drain, breaking up the hydrostatic pressure pressing against the wall and allowing the water to drain down to the foundation drain system. Do not let your contractor talk you into a lesser system.
But if digging everything up is not a good option, there is another solution for a wet basement. There is a product called Xypex that you can use. It is a cementitious material that is trowelled onto existing concrete block or reinforced concrete. It bonds to the concrete at a molecular level and forms a crystalline formation that makes the wall completely waterproof.
Unlike other waterproofing paints, it can be applied to wet surfaces. The finished surface will be a light grey, stucco-like surface. The product is fairly expensive, but nowhere near the cost of digging, etc. and you can apply it yourself, if you want to save some costs.
Do not kid yourself. There is no such thing as a basement that is only "a little wet" when it you plan on finishing it off and enjoying the added living space. Water in your basement will ruin your remodeling and plague you for years to come. It's worth the effort and expense to solve the problem the right way.
Once the wetness problem is cured, you'll still need to make sure your basement does not feel damp and smell musty. These are issues of air quality within the basement and really have nothing to do with water infiltration. I discuss this in my article about Building a Basement.