Home Tips & Advice

Waterproofing Your Basement

Read these tips and instructions carefully on how to waterproof your basement. Following the procedures outlined in this document will help you end up with a more satisfactory job-with less waste and effort. Inside this brochure you will find information about:

  • Stopping Leaks and Seepage
  • Repairing Holes and Cracks Before Waterproofing
  • Closing Cracks and Holes When Water is Entering Under Pressure
  • Waterproofing the Wall and Floor After Making Patching and Repairs
  • Packing a Leaking Floor Joint


  • If you're bothered with leaks or seepage through your basement floor or walls, the problem can be solved. However, it takes time and effort, and you have to do the job right. But it can be done.
  • There are three basic causes of seepage and cracks in basements. First, the original workmanship may be poor. Second, the house may have settled, causing cracks in either the floor or walls. Finally, water pressure from the outside may have built up and be forcing water through the walls.
  • Such leaks are easy to detect (see image). Moisture often begins to seep through at the area where the floor and walls joins or along cracks that may appear in the wall or floor.
  • If there are no holes or cracks in the basement walls, you can apply a waterproofing compound directly to the walls by steps described later. However, almost all basement leaks are caused by either cracks or holes in the walls or floors that should be repaired before waterproofing is applied.
  • You can usually fill hairline cracks with a regular waterproofing mix. However, cracks larger than 1/8" should be cleaned out and patched before you apply the waterproof mix (see image).
  • You can purchase special epoxy and latex cement formulas for mortaring small repair jobs or for brushing on as a waterproof coating. However, for a large repair job, you will probably want to mix your own mortar for patching holes and cracks before you start applying the waterproofing coat.
  • Mortar for filling holes and cracks in cement basement walls or concrete block walls is usually made by mixing one part cement and two parts of fine sand with just enough water to make a rather stiff mortar.
  • If the water is merely seeping through the basement wall, force the mixture of mortar cement into the crack with an ordinary trowel or putty knife. This should correct any leakage problem.
  • However, if outside pressure is forcing water through the wall, the problem is often extremely difficult to correct.
  • If water is seeping in under pressure, you must chip out a dovetail groove for the entire length of the cracked area (see image). Use a regular chipping chisel and hammer or a cold chisel to make a dovetail groove.
  • This image shows both the correct and incorrect ways to enlarge the cracked area before mending it. Use a chipping or cold chisel to create a dovetail space. This provides a holding area for the new mortar.
  • An incorrect groove, as illustrated, causes the mortar to fall out of the repaired area when it dries. Take time to do it right-it will pay off in the long run.
  • Repair holes in a concrete or concrete block wall in the same manner. Chip out the faulty or broken area in dovetail fashion. The dovetail cut (see image) provides a holding edge for the new mortar.
  • When the faulty cement around the edge of the hole has been completely chipped away, fill the hole with the same mortar mix recommended for filling cracks (see image). This mixture is one part cement to two parts fine sand mixed with just enough water to create a stiff mortar.
  • Place the mortar in the newly cleaned hole, and smooth it out with an ordinary trowel. Be sure the mortar is pressed into all parts of the hole, leaving no air pockets.


  • You may need to position a weep pipe through the wall to permit the outside water trapped against the wall under pressure to escape.
  • In many cases, the weep pipe need only be temporary. In other cases, it is necessary to leave it in place and drain the water away through a basement sewer trap or with a sump pump (see image).
  • Insert the weep pipe at the point where the wall and the floor join or at the point where the pressure is greatest.
  • Use regular patching mortar to fill the crack, starting at the top and working toward the bottom. This permits a more secure bonding of the new mortar.
  • Use an ordinary pointing trowel. Completely fill the crack with mortar to where the weep pipe is installed.
  • Let the mortar set until it is completely dry. If the water entering through the weep pipe has slowed to a trickle, you can probably remove the pipe, fill the hole and eliminate the problem.
  • However, if water is still coming through the pipe with considerable force, leave the weep pipe in place and run the water into a sewer drain with a hose.
  • If you decide to remove the pipe and patch the hole, treat the cracked area right down to the spot where the wall and the floor come together (see first image below).
  • Next, make a cement plug from the mortar mix. Roll the plug into a cone shape that is slightly larger than the hole (see second image below).
  • Roll the plug of cement in your hands until it begins to stiffen. Then place the small end of the cone-like plug in the hole where the pipe was removed and tamp it into place (see third image below). It can be tamped just like a cork in a bottle.
  • Hold the cement plug in place with your fingers for three-to-five minutes, allowing it time to set. Place a heavy object over the plug during this three to five minute period to give it plenty of time to dry before it is exposed to the full water pressure.
  • After this period, remove your hand or the object holding the plug in place. By this time, the mortar plug should be dried sufficiently to close off the hole and prevent outside water from entering.


  • Fill and patch all holes and cracks according to these instructions. Then, you are ready to apply the waterproof mix.
  • First, moisten the basement wall with a fine spray before applying the waterproofing mix. Use a garden hose with the nozzle set to a fine spray. Although the walls should be damp when you apply the waterproof mix, no water should be standing on the wall surface.
  • You can purchase epoxy or latex waterproof mixes for treating basement walls and floors. Most of these mixes require you to add only water. If you use this type of mix, be sure to follow the manufacturer's instructions carefully.
  • Many waterproof mixes will not adhere to painted walls. You must first remove the old paint by sanding, wire brushing or sand-blasting the surface before the waterproof mixture will adhere.
  • It is also important to remember that no epoxy or latex waterproof coatings will bond to wet surfaces. Apply these materials to a surface that is completely dry.
  • If you prefer, you can make your own wall coating mixture of plain cement and water. The mix should form a slurry-a mixture that is the consistency of cream.
  • Use a stiff brush and a circular motion to rub the waterproof mix into the wall. Take time to fill every pore in the wall (see image above).
  • First apply the coating at the bottom of the wall. This is where the water pressure is likely to be greatest.
  • Now brush the waterproofing mix to the top, then move back to the bottom, slowly applying additional layers of the mixture.
  • Brush the waterproofing mix only over the area where seepage or leakage is a problem (see image above). Feather the mix out at the edges until you have completely covered the area where the leakage or seepage has occurred.
  • When the coating has dried so that it does not rub off, spray the area completely with water. Soak it thoroughly and let it set overnight.
  • After the wall has dried overnight, wet it down thoroughly with a garden hose and apply a second coat of the waterproofing mixture while the wall is still wet (see image). Use the same techniques for brushing on the second coat as you did for the first coat.
  • Use two coats in all cases. One coat simply will not correct the problem under normal conditions.
  • In many cases, the leaking problem in a basement is near the joint at the floor and wall. If the leaking is not a serious problem, you may be able to correct it by troweling on a double layer of waterproof coating at the floor joint.
  • Use an ordinary waterproof coating mixture as previously described. Be sure the floor is clean where the mixture is applied.
  • If the seepage of water is heavy, cut a dovetail joint where the floor and wall join (see image).
  • Use a chipping chisel and a hammer or an ordinary cold chisel.
  • Chip along the entire floor joint area to create a dovetail groove that will retain the waterproof mix (see image).
  • Take time to chip this groove the complete length of the leaking area. This is one of the most important steps in the repair job.
  • After the dovetail groove has been completely chipped away, clean it out thoroughly and prepare to apply the waterproofing mix. Use an ordinary brush or a tire pump to brush or blow the small pieces of cement out of the chipped area.
  • The chipped-out area is now ready for the mortar. Use the regular mixture of one part cement to two parts fine sand plus water. You can also use ready-mix ingredients.
  • Apply small amounts of the cement mix into the chipped-out area and smooth it out with an ordinary trowel. Do not apply more cement than you can trowel down in two to three minutes.
  • Make a slight incline in the patched area, slanting it from the floor upward toward the wall. This provides extra strength to the patched area and helps drain away any moisture that might accumulate in the future.
CementSpray Nozzle
Cold ChiselStar Drill
Light BrushWire Brush
Epoxy or LatexWaterproofing Mix
Garden HoseChipping Chisel
Pointing TrowelHammer
Work GlovesStiff Brush
Hand CleanerWeep Pipe

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Check your state and local codes before starting any project. Follow all safety precautions. Information in this document has been furnished by the North American Retail Hardware Association (NRHA) and associated contributors. Every effort has been made to ensure accuracy and safety. Neither NRHA, any contributor nor the retailer can be held responsible for damages or injuries resulting from the use of the information in this document.

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