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Another common source for humidity in a basement is external water, which can come from precipitation or groundwater. Gutters are designed to collect precipitation and move the water away from your house, but they have to be free of debris to work properly.Clean your gutters every spring and fall to remove leaves, dirt, pinecones, and other matter that could clog the spouts. When gutters become clogged, water builds up inside and drips over the edges. The water then collects around the base of your house, and may seep in through the foundation. Sump pumps, which are found in the basement or bottom floor of the house, should be inspected annually. Check that the pump is in good working order, that the pump is upright, and that it’s properly pumping water away from the house.  A sump pump system collects water from around the foundation of the house, drains it into a sump pit, and then pumps the water away from the house. In order to perform this task, the sump system has to be properly cleaned and maintained. Not all houses have sump pumps. If you're not sure, check your basement for the sump pit, which is a large reservoir dug into the floor to collect water. Some basements just have a dirt floor, and water vapor can easily enter the basement through the soil. To prevent this from happening, cover the floor with sheets of 6-millimeter plastic. Overlap the seams of the plastic to prevent moisture from getting through, and attach the plastic to the walls with tape or staples. Holes, cracks, and other openings in the foundation are easy ways for moisture to enter your basement. Small holes can be repaired with a polyurethane masonry caulk, but you should use hydraulic cement to fix larger holes.  Typically, you can address a small crack in the foundation as long as it’s vertical. Call in a professional if the crack is horizontal, diagonal, or growing, or if you want it assessed by an expert. The foundation is the structure on which your house is built, so it’s always best to consult an expert if you're unsure of a problem. Most foundation material is porous, including concrete and stone. This means water can seep into your basement through the foundation. There are several products you can apply to your basement walls to make them waterproof, and they can be applied like paint. Look for masonry waterproof coatings like Xypex or Drylok.
Keep your gutters clean. Maintain your sump pump. Cover dirt basement floors with a plastic barrier. Fix holes or leaks in the foundation. Coat the walls with a waterproof material.