How to Waterproof & Seal Concrete


Whether used in floors, foundation walls, patios or garages, unsealed concrete can cause a variety of issues. Since concrete is a porous material, water absorbs into the concrete floor or wall, and if enough moisture is present, this absorption may lead to leaks or even weaken the concrete. You can prevent these problems by waterproofing and sealing concrete wherever it is used in or around your home.

Things You'll Need

  • Canned air or wire brush
  • Concrete patching compound
  • Putty knife
  • Medium-grit sandpaper
  • Bucket
  • Anti-grease soap
  • Soft-bristled cleaning brush
  • Garden hose or wet rags
  • Plastic sheeting
  • Masking tape
  • Paint tray
  • Concrete sealer
  • Paintbrush
  • Paint roller
  • Repair any holes or cracks in the concrete before waterproofing to prevent complications later. When you locate a hole or crack, remove any loose pieces by blowing into the space with canned air or brushing over the space with a wire brush. Mix up concrete patching compound according to the manufacturer's directions and spread the patching compound over holes and cracks with a putty knife until each hole or crack is filled to level with the surrounding surface.

  • Check the patched holes or cracks after three to four hours when the concrete patching compound is dry. If the compound does not sit evenly with the surface, fill in the gaps with more compound and allow it to dry. Continue this process until the holes or cracks remain filled to the surface.

  • Sand off any patching compound that protrudes from the surface with medium-grit sandpaper to level it with the wall. Make a batch of soapy water in a bucket, using anti-grease soap, and clean the wall once all the holes and cracks are properly filled with a soft-bristled cleaning brush and the solution.

  • Spray the soapy residue from the concrete surface if the area has the proper drainage to remove the water. If not, use wet rags to wipe down the surface and remove any soap.

  • Cover surfaces that touch the concrete surface with plastic sheeting. Apply tape around the entire perimeter of the sheeting to hold it in place.

  • Fill a paint tray with concrete sealer. Begin in one corner of the room and use a paintbrush to apply sealer to 5 to 6 inches around the outside edges of the concrete where it comes into contact with walls, the floor and ceiling, or any other fixtures that touch it.

  • Apply the sealer to the rest of the surface with a paint roller. Begin each application with the roller by placing the roller on the surface at the end of the last section of sealer applied, and then move the roller backward a few inches into the area where the sealer has already been applied before continuing forward. This limits visible streaks in the sealed surface.

  • Let the sealer dry on the concrete for a few hours until it feels dry to the touch, and then apply at least one additional coat to the concrete. If you choose to apply more than one additional coat, allow each coat of sealer to dry before applying the next coat.

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