How to Fix a Leaking Balcony Flat Roof

Scrub the leaking sections, such as cracks and around damaged projections, with a wire brush to detach crud. Sweep all grime off the balcony roof using a broom.

Put on full-length clothing, eye protection and rubber gloves. Many roof patching compounds, such as plastic cement, contain toxic chemicals.

Spread plastic roof cement around a leaking roof projection using a trowel. Make the cement bed 1/8-inch thick and spread three inches beyond the projection. Don’t let the roof cement dry.

Lay fiberglass reinforcing fabric over the moist bed of cement. Using the trowel, press the fiberglass fabric into the cement.

Coat the fiberglass fabric with a 1/8-inch-thick layer of roof cement. Use the trowel to smoothly spread the cement three inches beyond the projection, making the cement layer thinner toward the edges of the repair.

Let the sealed roof projection cure for three days.

Coat a crack in the balcony roof with a 1/8-inch-thick layer of rubberized roof patching cement using the trowel. Extend the rubberized cement three inches beyond the crack.

Lay fiberglass reinforcing fabric over the moist bed of rubberized cement. Using the trowel, press the fiberglass fabric into the cement.

Coat the fiberglass fabric with a 1/8-inch-thick layer of rubberized cement. Use the trowel to smoothly spread the cement three inches beyond the crack, making the cement layer thinner toward the edges of the repair.

Let the patched crack cure for two days.