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

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Instructions

1. 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.

2. 

   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).

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

4. 

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

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

Repairing in the rain

1. 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

1. 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).

2. 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.