Basement Waterproofing

A dry basement for work, hobbies, storage, and extra living space is an asset to any home. On the other hand, a wet, damp, musty basement taints the value of the entire house as an investment, and is a source of continuing annoyance and frustration for a homeowner.

The best general advice to anyone attempting to eliminate unwanted water from a basement is that all cures and options should be fully researched. 

A homeowner who examines the full range of possible causes and potential remedies will be far more likely to obtain effective and lasting repairs than one who settles for the first, easiest, or least expensive method proposed as a solution.

Look For Obvious Solutions

The cause of a wet or damp basement can be minor, readily apparent, and easily corrected. Here are some probable causes and possible solutions:

  • Problem: The source of water in the basement can not be identified.

    Solution: To determine whether the water is seeping in from the outside or condensing inside, tape a twelve-inch square of aluminum foil to a wall that is prone to dampness, sealing all four sides as airtight as possible. In a day or two, if the side of the foil that was against the wall is wet, the problem is seepage. If the outside is wet, it's condensation.

  • Problem: Lawns that are flat or slope toward the house permit surface water (rain and melting snow) to drain down against basement walls. Water enters through cracks or other openings in the walls and causes wet spots on the walls or standing water on the floor.

    Solution: Slope the ground away from the outside foundation (about one inch per foot). Extend the slope for at least ten feet. Seed it with a good lawn grass. Sodding is a common practice and prevents the washing away of newly graded areas during heavy rains.

    Where a large area of land slopes toward the house, surface drainage should be intercepted and redirected some distance from the house. Dig a shallow, half-round drainage ditch or depression designed to route the water around the house. Sod the ditch or plant grass in it. If even a shallow ditch is objectionable, drainage tiles, with one or more catch basins at low spots, may be installed.

  • Problem: Defective, clogged, or nonexistent gutters and downspouts allow roof water to form puddles, or wet soil near or against basement walls, and enter through cracks or openings in the masonry.

    Solution: Install gutters and downspouts wherever needed. Keep them free of debris. Where leaves and twigs from nearby trees may collect in a gutter, install a basket-shaped wire strainer over the downspout outlet or place screening across the length of the gutter. Repair gutters and downspouts as soon as the need appears. To prevent concentration of water at the point of discharge, use a concrete gutter or splash block to carry the water away at a slope of one inch per foot. Also, consider extending downspouts from rain gutters away from the outside foundation.

    Roof water can also be piped underground to a storm drain, dry well, or surface outlet fifteen feet or more from the house.

  • Problem: Dense shrubbery and other plantings around the basement walls prevent good ventilation.

    Solution: Trim heavy growths of shrubbery so that soil gets more sunlight and dries quicker. When digging up the plantings, remove any pieces of masonry, mortar, or other material buried near the house after the basement was excavated.
  • Problem: Unprotected basement window wells act like cisterns during heavy storms, permitting water to seep in around window frames and below windows.

    Solution: Windows or parts of windows below grade should be protected by metal or masonry window wells, with bottoms consisting of gravel to permit good drainage. Clear plastic bubbles are available to cover the entire window well like an awning.

  • Problem: Atmospheric moisture produces condensation ("sweating") on cool surfaces in the basement, particularly walls, floors, and cold water pipes.

    Solution: Insulate the water pipes. Promote good ventilation--sunlight and free movement of air can quickly dry out a basement. Ventilation should be regulated according to the weather conditions. During hot, humid weather or long rainy spells, windows should be closed because the outside air will probably contain more moisture than the basement air. Heat the basement during the winter. During hot weather, use air conditioning to cool and dehumidify the air.

  • Problem: Leaky plumbing or other sources of moisture--such as clothes hung to dry on basement lines--increase humidity in the air, causing condensation.

    Solution: Repair plumbing promptly, open windows or dry clothes in an automatic dryer vented outdoors. If the problem persists, experiment with using a large-capacity dehumidifier to eliminate condensation. Try borrowing one from a friend or neighbor before investing in what may turn out to be the wrong remedy.

    Concentrate On The Source Of Persistent Problems

    If every apparent, logical way of eliminating wetness fails to produce a dry basement, do not waste time or money on random potential solutions. Finding the cause of the problem is absolutely essential to its cure. The hardest type of water problem to correct is one created by faulty construction practices at the time the house was built. Proper drainage is a crucial consideration in selecting the site for a new house. This includes not only the drainage of surface water but also drainage of any subsurface or ground water that may already be present, or that may accumulate over a period of time and be blocked from its normal course of flow by the new construction.

    If the subsurface or ground water level is close to the underside of the basement floor slab, water rises through the slab by capillary action, producing dampness. If the subsurface or ground water level is higher than the basement floor, water leaks in through the walls and floor or enters by capillary action, causing standing water in the basement and, at times, dampness in the rooms above. Under ideal conditions, a house should be situated so that even during rainy seasons the subsurface or ground water level is at least ten feet below the finished grade--well below the average basement floor.

    In some cases, it is impossible to completely eliminate dampness from a basement whose construction did not take into consideration the basic principles of good drainage. Only after soil borings have been done can anyone knowledgeably predict which, if any, course of action has a chance for success.

    Weigh Alternative Methods Of Treatment

    An accurate diagnosis of the main cause of persistent basement wetness may lead to a recommendation of one or more of the following actions:

    • Redirect Water Away From Foundation

      The various exterior waterproofing barriers have varying levels of effectiveness in protecting the outside wall areas. But wall anti-leaking barriers do not affect water penetration due to water accumulation at the footer or floor level. The ideal solution to this problem lies in directing the accumulation of water away from the foundation or into drainage or pumping system.

    • Install An Interior Drainage System

      To control leakage in the basement, you may install a drainage system on the inner side of the foundation. The floor is broken up along the perimeter of the basement wall and drain tile is placed in a trench that carries the water to a discharge point, or sump pump, which takes the water away from the house. With hollow block walls, holes may be drilled at the bottom to allow the water to pass into the drain pipe and relieve the water pressure. The trench may then be filled with gravel and the floor replaced or recemented. If installed correctly this system will remove basement leakage water. Channels may also be installed on the basement floor to take the water away through a sump pump.

    • Apply Waterproofing Compounds To Interior Walls

      Only in cases where mild and occasional capillary seepage occurs are applications of waterproofing paint or other interior compounds likely to provide any lasting degree of improvement in achieving a dry basement.

      Capillary waterproofing materials can be applied to either exterior or interior wall and floor surfaces. If properly applied, they will penetrate several inches into concrete and close off capillaries or minor cracks by forming crystals in the presence of water. Do-it-yourselfers should carefully read the label to determine the waterproofing product's limitations and terms of any guarantee promised.

      Waterproofing paint is most effective if applied directly over cement; not existing painted walls.

    • Injection of Waterproofing Substances

      Into Exterior This type of treatment does not require excavation. Instead, sodium bentonite or another substance--sold under a variety of trade names--is injected into the space between the soil mass and the basement wall. It swells to many times its dry volume when it is first put into slurry form. The slurry will tend to penetrate and plug cracks where water might also find a path to the basement interior, thus reducing the flow of water.

      The type of soil and the skill of the person directing or performing the injection operation has a strong bearing on the success of this method to correct basement wetness.

      Certain chemicals, such as salt, will tend to prevent the effectiveness of the sodium bentonite, and undetected underground barriers (such as rock or wood) can seriously impair the effective use of this method.

      In very pervious, coarse sand to gravel soils, the soil itself can be injected with bentonite slurry, but it may not be possible to inject bentonite slurry into clay soils, silt soils or sandy soils where the sand is of fine to medium gradation.

      The injection of sodium bentonite slurry beneath a basement floor might result under certain circumstances in the floor being raised by hydrostatic pressure, and tend to plug any drain tile that might exist under the floor.

      Under Title I, Property Improvement Loan Program, the U.S. Department of Housing and Urban Development (HUD) "does not permit loans to be made for waterproofing of a structure by pumping or injection of any substance in the earth adjacent to, or beneath the foundation, or basement floor."

    • Excavate

      Sometimes it is necessary to resort to the extreme measure of exposing the basement walls, treating them to make them watertight, and then regrading the soil. Among possible treatments are:

      Covering the walls with a prepared waterproofing felt or fabric coated and cemented together with hot coal-tar pitch. If properly applied, the membrane is a very effective method of waterproofing. However, it is very expensive, and if subsequent leaks develop they may be difficult to locate and repair. Remember, water can still come in through the basement floor.

      Applying two coats of portland cement mortar to the surface of exterior walls. Called parging, this work should be done only in dry, mild weather. Fall is the best time, because the subsurface water level is usually low and temperatures are more favorable for making watertight concrete.

      The newly cemented walls should be properly protected and cured. Freezing or rapid drying of the concrete by sun or wind can damage it and make it worthless. In very wet soils, the parged wall surfaces may be given two coats of hot coal-tar pitch.

      Keep in mind that settlement and thermal expansion and contraction of the wall can affect the parging; preventing it from bridging cracks that develop in the walls.

      Applying polyethylene or polyvinyl film, a vapor barrier material, to the exterior surface of the walls. Manufacturers' instructions should be followed in applying the material.

      Installing drain tile around the footings, at least on the sides where trouble is occurring. This procedure is generally recommended in addition to one or more methods above.

      Good, four-inch drain tile should be used, laid parallel with, and at the bottom of the footings. Great care must be taken to see that the bottom of the tile is not lower than the bottom of the footings, so that the footings are not undermined.

      In normal, porous soil, the tile should be covered with 18 inches of screened gravel. In heavy, non-porous soil, the gravel should extend almost to the top of the excavation.

      This footing drain and belt of gravel should drain off all seepage water and prevent the accumulation of water around the walls. This method is especially suitable on the upper side of a house located on a hillside.

    Choose A Waterproofing Contractor Carefully

    A properly applied waterproof barrier may prevent the water form seeping through the wall, but allow it to seep deeper into the ground until it finally comes through around the footer or basement floor. Thus, it is critical that a knowledgeable and competent contractor evaluate the problem.

    Deal with a waterproofing company that has a good reputation in the community--one that has been in business in the same area for several years, and depends on the satisfaction of its customers. Find out if the company is bonded, licensed and certified (where applicable). Also, find out if the company trains its workforce through apprenticeships or other training programs.

    Beware of salespersons or contractors who ask for large payments in advance. Reliable contractors generally do not require more than a minimal downpayment.

    Obtain written estimates from at least three contractors. Compare the cost of the work to be done, the quality of materials to be used, and the cost of financing the work. Insist that each estimate include the cost of materials and labor and a statement of exactly what the contractor will do and how long the work will take.

    Check each contractor's reliability with the local Better Business Bureau, previous customers, and friends who have dealt with the same problem.

    Tips To Remember

    • After selecting a contractor to do the work, ask for a written contract in accordance with the estimate. Read this contract carefully before you sign it. Make sure you understand its contents. If you have a question, ask an attorney to review the contract for you. The contract should include the following:
      1. The contractor's name, address, telephone number.
      2. A full description of the work to be done and a list of the materials to be used.
      3. A definite date on which work will start and the length of time for completion.
      4. A provision that no change in plans or specifications may be made without the homeowner's written approval.
      5. A requirement that the contractor will obtain any necessary permits or licenses to assure the homeowner that building codes will not be violated.
      6. Details of payment -- the down payment, monthly payments, number of payments, the total finance costs, and annual percentage rate. The annual percentage rate is your key to comparing costs for the lowest rate.
      7. A statement that the contractor is responsible for insuring his employees against possible injury on the job.
      8. A warranty or guarantee with all conditions spelled out. For example, if what the contractor provides doesn't solve the water problem, what is the company obligated to do and what are the alternatives?
      9. The contractor's signature and local or state licensing number, if licensing is required.
    • If you plan to finance the work and the contract terms could give the contractor a lien, mortgage on other security interest on your home, or if you are solicited by a door-to-door salesperson, make sure the contract contains a provision allowing you to cancel within three business days after signing it without penalty.

    • When signing the contract, make sure that all blanks are filled in, and that it contains everything the contractor promised. Do not rely on oral guarantees.

    • Make sure you have a copy of the written contract, signed by both parties, should you have trouble with the contractor later.

    • If and when the contractor requests your signature on a completion certificate, inspect the job carefully to see that the work has been done satisfactorily, before signing.

    • Even if the job is finished, do not sign the completion certificate if you have a valid complaint about the work. It is not unreasonable, for basement waterproofing work, to delay signing until after heavy rains have come, or a specified period of time has elapsed.