How to Seal a Concrete Foundation


Because you have only one opportunity to seal a concrete foundation it is imperative it be completed correctly the first time. Concrete foundation cracks occur due to concrete shrinkage, building materials and soil settlement or hydrostatic pressure caused by earth. Deficient applications of a sealant can affect the structural integrity of a concrete foundation, cause damage to the finished structure and result in enormous costs to correct damages because of inadequate products, sealing methods or practices.

Things You'll Need

  • Protective clothing
  • Sealant (liquid membrane)
  • Wire brush
  • Paint brush, roller or sprayer
  • Carefully select the product that best suits your needs as there are many different products available to seal a concrete foundation. It is important to follow the manufacturer's directions closely when applying any concrete sealant. Prepare concrete surfaces to receive sealant. Use wire brush to clean surfaces. Clean all existing surfaces and ensure they are free from dirt, stains, grease, oil or loose material, etc. Use power washer if necessary. Fill all joints and repair cracks in concrete and allow to thoroughly dry. Make certain surfaces are completely dry before applying sealant.

  • Trowel grade or fill any voids such as wall-footing joints with an appropriate material (cement). Address any issues with remaining concrete forms, pipe penetrations, etc. to keep other trades from disturbing or possibly puncturing the sealant. Apply sealant with brush, roller or sprayer evenly over all surfaces maintaining consistency in thickness. Achieve minimum coverage of approximately 60 mils. Sealant should be applied as close to grade as possible. Extend coverage onto surfaces such as intersecting walls not designated to receive sealant for added protection. Protect form-tie holes below grade.

  • Provide protection to sealed surfaces from backfilling procedures. Select a protection method such as one inch thick expanded polystyrene foam board and adhesive that is compatible with the sealant applied. Do not allow traffic on foundation floor slabs treated with a sealer.

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