How to seal an outdoor mural

Updated February 21, 2017

Murals have been painted outdoors for centuries, starting with ancient cave paintings dating back thousands of years. They can take many hours to paint and add an artistic flair to buildings, fences and other paintable surfaces. To ensure artwork is protected from both the sun and weather elements, follow these simple steps to seal outdoor murals properly.

Purchase a clear polyurethane sealer from a local hardware or paint store. Determine what type of sheen the mural should have---satin and glossy work well in outdoor environments. Look for products that claim to be non-yellowing and that contain UV protection from harsh sunlight.

Check the weather for the day and evening prior to painting. Avoid painting in overly humid weather or when rain is possible. Do not paint when temperatures fall below 10 degrees C. The temperature must remain above 10 degrees C for 24 hours for proper curing of the topcoat.

Use painter's tape on any areas where the sealer should be avoided, such as door frames, windows and trim. Use drop clothes to protect the ground surface, even when working outdoors. Wear goggles, a mask and latex gloves for additional protection.

Put the sealer into a 22-litre (5-gallon) bucket. Hang a paint grid inside the bucket. Dip the roller into the sealer and roll several times onto the paint grid to release excess solution. Quickly roll the sealer over the mural using vertical strokes. Do not over-roll the sealer or continue to roll if the sealer has started drying. Roll as close to the perimeter as possible.

Use a paintbrush to paint any areas missed by the roller. The perimeter of murals often must be painted with a paintbrush. Allow the mural to dry. Add a second or third coat of sealer for added protection. Look at the mural from an angle to determine if any spots where missed. Identify spots by looking for a difference in sheen levels on the mural.

Add signs around the area that state "Wet Paint" to avoid fingerprints on the wet surface. Clean all tools with warm water.


Avoid thick layers of sealer, especially over dark colours. The sealer can become cloudy and leave a white film that cannot be removed. Always apply the polyurethane in thin layers. Before applying the sealer to the entire surface, always test the topcoat for any reaction between the sealer and paint.

Things You'll Need

  • Clear UV protective polyurethane
  • Painter's tape
  • Dust sheets
  • Plastic
  • Goggles
  • Mask
  • Latex gloves
  • 22-litre (5-gallon) bucket
  • Paint grid
  • Paint roller
  • Roller frame
  • Paintbrush
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About the Author

Julie Hampton has worked as a professional freelance writer since 1999 for various newspapers and websites including "The Florida Sun" and "Pensacola News Journal." She served in the U.S. Army as a combat medic and nurse for over six years and recently worked as the Community Relations Director for a health center. Hampton studied journalism and communications at the University of West Florida.