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How to seal exterior brick to stop water penetration

Updated February 21, 2017

Brick is a durable construction material, although it is quite porous. When it rains, the pores in the brick soak up the water falling on it. If your home has just one layer of brick, the absorbed moisture can at times travel through the brick layer and penetrate the interior of your home. To prevent or stop a moisture problem, simply seal the brick to close its pores and prevent moisture absorption.

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Wet the surface of the brick with the garden hose.

Scrub the brick clean with the long-handled brush and trisodium phosphate (TSP) powder diluted in water according to the manufacturer's instructions. Scrub from the top to the bottom, then rinse the brick clean and allow it to air dry for at least 48 hours.

Cover the brick adjacent to the edge of windows, awnings or doors with painter's tape. If you intend to use a paint sprayer, cover windows and doors with plastic sheeting to prevent accidental over-spray.

Stir the water repellent vigorously, using the paint paddle.

Apply the water repellent to the surface with the paint sprayer or long-handled paintbrush, following the manufacturer's instructions. If the repellent accidentally finds its way onto any metal or glass surfaces, wash off immediately with soap and water.


Repair any holes or cracks in the brick before you apply the sealant. There are two major categories of moisture protectants for brick: film-forming sealants and penetrating water repellents. Use penetrating water repellent, as film-forming sealants prevent water from entering as well as escaping the brick, allowing any trapped water to deteriorate the brick. Newly applied brick must cure for at least 28 days before repellent can be applied. Only apply repellent when temperatures are 4.44 to 37.8 degrees Celsius and winds are below 15 miles an hour. If you are using a paint sprayer, be sure to flush the system with soap and water, according to the manufacturer's instructions, as soon as your application is finished.

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Things You'll Need

  • Goggles
  • Penetrating water repellent
  • Painter's tape
  • Plastic sheeting
  • Bucket
  • Trisodium phosphate (TSP) powder
  • Long-handled scrub brush
  • Hose
  • Paint roller
  • Paint sprayer
  • Paint paddle

About the Author

Based in Houston, Texas, Meg Butler is a professional farmer, house flipper and landscaper. When not busy learning about homes and appliances she's sharing that knowledge. Butler began blogging, editing and writing in 2000. Her work has appered in the "Houston Press" and several other publications. She has an A.A. in journalism and a B.A. in history from New York University.

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