How to Waterproof a Balcony

There's nothing quite like a nice balcony or deck to make your house a home. Sitting and watching the sunset with a drink in hand, or the sunrise with coffee, is better on your balcony. Perhaps you just want to sit around with family and friends telling a story or sharing a meal.

Waterproof your balcony and enjoy the view.

To keep your balcony or deck beautiful, you should waterproof it. You can put a wood sealer on a wood balcony and preserve the rich wood look, but a liquid membrane over the top allows you many more decorative options such as ceramic tile. Additionally, it protects areas below the balcony from water penetration.

  1. Mix a bucket of hot water with liquid detergent, or use a commercial deck cleaner. Scrub your balcony using a push broom and the cleaner, leaving the cleaning solution for 20 or 30 minutes after application to allow it to penetrate any stains or residues.

  2. Spray the cleaning solution off your balcony using a pressure washer or, alternately, a hose with spray attachment. Rinse thoroughly. Allow your balcony to dry at least two days before proceeding. Moisture inside the wood or concrete may evaporate slowly.

  3. Sand any rough edges, uneven joints, or other problem spots in your balcony, if it is wood. Fill any knot holes, nail holes, or other voids with acrylic caulk. Use a putty knife, or your gloved finger, to wipe excess caulk away after application and make it flush with your balcony or deck surface.

  4. Tape any joints, such as between balcony floor materials or between the balcony and the house. Use a polyester tape for any cracks or other large gaps. Use a small paintbrush and apply a thin layer of liquid membrane, centered over the joint or crack. Quickly stick the polyester tape on top and smooth into place. Cover with another thin layer of liquid membrane.

  5. Cut and adhere flashing to the door sill, using nails or construction adhesive. Make sure it is flush with the surface. Cover with a layer of liquid membrane to coat thoroughly. Once the membrane is installed and dried, sand the edges of the membrane covering any taped and flashing areas to smooth the finished appearance.

  6. Using a paint roller, apply a continuous layer of liquid membrane. Work lengthwise to boards, if the balcony is wood, to allow the membrane to fill the seams better. Direction does not matter as much on concrete or completely smooth surfaces. The amount of membrane needed varies according to product specifications -- typically between 3/4 of a gallon per 100 square feet to three gallons per 100 square feet. Consult product instructions to verify.

  7. Follow with a second application of waterproof membrane once the first layer is dried -- about an hour or two. Spread this layer the same thickness as before. Allow it to dry another couple of hours.

  8. Apply a topcoat to add color and slip-resistance to the balcony surface. Paint on two layers at a rate of approximately a gallon per 200 square feet. Dry an hour or two between and after coats.

  9. Finish by spreading a very thin layer of sealer with a paint roller. This provides a semi-gloss finish along with additional waterproofing. Use about a gallon per 200 square feet.

  10. Tip

    Choose a time when bad weather is not forecast for at least 24 hours. Temperatures should be between 50F and 90F. Moisture and humidity delays curing time. Do not walk or place heavy objects on the balcony surface for at least two days to avoid damage to your waterproofing.