How to Patch a Flat or Low-Pitched Roof


Flat-roof patches are temporary fixes. You should plan to replace them with a permanent repair as soon as is practical, unless you'll be reroofing in the next year or so.

Things You'll Need

  • Fiberglass Reinforcing Cloth
  • Plastic Roof Cement
  • Cloth
  • Window Cleaner
  • Brush
  • Disposable Trowel Or Wide Putty Knife
  • White Gas Or Splicecleaning Fluid
  • Utility Knife
  • Caulking Gun
  • Butyl or polyurethane sealant, or peel-and-stick roofing tape
  • Brush aside the existing gravel (in a built-up roofing system) and scrape off any that remains in the area you're patching. For double-coverage roll-roof systems without gravel, just brush and/or blow off dirt, loose materials and dust.

  • Trowel plastic roof cement over the damaged area and about 6 inches (15 cm) around it using a disposable trowel or wide putty knife (see A).

  • Immediately embed a layer of fiberglass cloth into the cement, pressing it lightly with the trowel or wide putty knife.

  • Apply a second layer of cement over the fabric (see B).

  • Allow the patch to dry and preferably withstand the test of another rainstorm before you cover it with gravel.

Repairing in the rain

  • In the case of sudden damage--caused by, say, a fallen tree limb or a storm that blows loose an object anchored to the roof--make an immediate repair, even in the rain, to limit interior damage. Use a roof cement formulated for application on a wet roof.

Repairing a rubber roof

  • Clean the damaged area with window cleaner, then wipe it using a cloth dampened with white gas or splice-cleaning fluid (available from a roofing supplier).

  • Cut the tip off a caulking gun and use it to apply butyl or polyurethane sealant to the tear or hole, then smooth the sealant with a trowel. Alternatively, use a peel-and-stick roofing tape and apply weight to press it firmly into place.

Tips & Warnings

  • Never make a repair if there is any danger of lightning.
  • Walk and work carefully on a built-up roof to avoid damaging it.
  • Protect your hands with rubber gloves when cleaning a rubber roof or work gloves when installing a roof patch.

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