How to Waterproof Your Basement

a basement
  • 72-168 hours
  • Advanced
  • 200-400
What You'll Need
Cold chisel
Light brush
Epoxy or latex
Garden hose
Pointing trowel
Work gloves
Hand cleaner
Spray nozzle
Star drill
Wire brush
Waterproofing mix
Chipping chisel
Stiff brush
Weep pipe

Basement walls are well known for weeping and leaking. All that moisture can cause big problems. The good news is that you can waterproof your basement with a few basic steps. In order to protect it, you will need to stop leaks and seepage, repair holes and cracks, waterproof the walls and floors, and pack a leaking floor joint. Follow the procedures outlined in this DIY article to save both waste and effort while achieving superior results.

Stopping Leaks and Seepage

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 accumulated and forced water through the walls.

Such leaks are easy to detect. Moisture often begins to seep at the area where the floor and walls join, or along cracks that may appear in the wall or floor.

Repairing Cracks and Holes Before Waterproofing

basement with white walls

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 in this article. Almost all basement leaks are caused by either cracks or holes in the walls or floors. They should be repaired before waterproofing is applied.

Step 1 - Clean and Patch

You can usually fill hairline cracks with a regular waterproofing mix; however, cracks larger than 1/8-inch should be cleaned and patched before you apply the waterproof mix.

Source Waterproofing Mortar on Amazon

Step 2 - Prepare the Mortar

You can purchase special epoxy and latex cement formulas for mortaring small repairs or for brushing on as a waterproof coating. For a large repair job, you should mix your own mortar before applying the waterproofing coat. Mortar for filling holes and cracks in cement basement walls or concrete block walls is usually made by mixing 1 part cement and 2 parts fine sand with just enough water to make a stiff mortar.

Step 3 - Chip a Dovetail Groove

If water is seeping under pressure, you must chip-out a dovetail groove along the entire length of the cracked area. Use a regular chipping chisel and hammer or a cold chisel to make a dovetail groove. The carved space provides a holding area for the new mortar. An incorrect groove allows the mortar to fall from the repaired area when it dries.

Step 4 - Apply the Mortar

Force the mixture of mortar cement into the crack with an ordinary trowel or putty knife. Doing so should correct the problem; however, if outside pressure is forcing water through the wall, the problem is often extremely difficult to correct.

Step 5 - Repair the Rest of the Concrete

Repair holes in a concrete or concrete block wall in the same manner. Chip-out the faulty or broken area in a dovetail shape. The dovetail cut 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 that was recommended for filling cracks. Apply the mortar to the newly formed groove and smooth it with an ordinary trowel. Ensure that the mortar is pressed into all parts of the hole, leaving no air pockets.

Closing Cracks and Holes

concrete floor

Step 1 - Insert Weep Pipe

You may need to position a weep pipe through the wall to permit the outside water that is 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 with either a basement sewer trap or a sump pump.

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. Doing so creates a more secure mortar bond.

Step 2 - Fill the Crack

Use an ordinary trowel. Completely fill the crack with mortar until you have covered the area 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.

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 down to the spot where the wall and the floor come together.

Step 3 - Make a Cement Plug

Make a cement plug from the mortar mix. Roll the plug into a cone shape that is slightly larger than the hole. 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. It can be tamped just like a cork in a bottle.

Hold the cement plug in place with your fingers for 5 minutes, allowing to set. Place a heavy object over it while it sets to allow plenty of time to dry before the plug is exposed to the full water pressure.

Waterproofing the Wall and Floor After Patches and Repairs

Step 1 - Moisten

Moisten the basement wall with a fine spray before applying the waterproofing mix. Use a garden hose with the appropriate nozzle setting. Although the walls should be damp when you apply the waterproof mix, no water should be standing on the wall surface.

Step 2 - Prepare the Epoxy

Purchase epoxy or latex waterproof mix for treating basement floors and walls. Most of these mixes require you to add only water. If you use this type of mix, 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. If you prefer, you can make your own wall coating mixture from plain cement and water. The mix should form a mixture that is the consistency of cream.

Step 3 - Apply the Epoxy

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. Apply the coating at the bottom of the wall, which is where the water pressure is likely to be greatest.

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. Feather the mix at the edges until you have completely covered the problem area.

Step 4 - Apply a Second Coat

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. Once the wall has dried, wet it thoroughly with a garden hose and apply a second coat of the waterproofing mixture while the wall is still wet. Use the same techniques to apply the second coat as you did for the first coat. Use two coats in all cases. A single coat simply will not correct the problem under normal conditions.

Packing a Leaking Floor Joint

Most basement leaks occur near the joint at the floor and wall. If the leak is not a serious problem, you may be able to correct it by cutting away chipped edges to create a groove and troweling a double layer of waterproof coating at the floor joint. Use an ordinary waterproof coating mixture as previously described.

The chipped-out area is now ready for the mortar. Use the regular mixture of 1 part cement to 2 parts fine sand, plus water. You can also use ready-mix materials. Make a slight incline in the patched area, slanting it from the floor upward toward the wall. Doing so provides extra strength to the patched area and drains moisture in the future.

Safety and Building Codes

Check your state and local codes before starting any project. Follow all safety precautions. Information in this document has been furnished by the National 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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