How to Seal a Flat Roof for a Tile Roof

What You'll Need
Rubber gloves
Pocket knife
Fluorescent marker
Metal putty knife
Roofing cement
Alcohol based cleaner (Windex)
Roof patching material
Roof tape
Straw broom
Trash bag

Sealing a flat roof to install a tile roof is not a particularly hard job, but does require that the work is done carefully and with a concentrated sense of detail. Because a flat roof isn't perfectly flat, there are areas where pooling of water will occur. These areas must be immediately repaired to prevent further damage to your roof structure.

One of the main reasons that water has the opportunity to collect on your flat roof is that the drainage slope becomes inoperable because of failed maintenance procedures or it is improperly installed. Identifying the issue and making the necessary repairs is a priority when considering installing a tile roof.

Step 1 - Identify the Problem Areas

With your gloves on and ladder in place, climb on your roof to identify any areas that show cracks or bubbles and defects in the coating. Look over all seams to ensure that the roof tar is properly in place. Use your pocket knife to check a seam that appears to be an issue. Slide the blade of the knife beneath the overlap of the seam. If your blade freely moves an inch or more beneath the overlap, you will need to repair this area.

Step 2 - Mark the Defective Areas

Use your marker or light colored spray paint to identify the areas that need attention immediately. This will help you to avoid guessing where the spot was when you get to the repairing stage of the process.

Step 3 - Prepare the Areas for Repair

To ensure that the repairs you make are not compromised shortly after completion, it is necessary to clean the areas before attempting the repairs. Sweep up all loose debris and use the metal putty knife to scrape away hard to remove roof gravel to expose the membrane. Place all debris in a trash bag.

Step 4 - Apply Roofing Cement

After areas have been thoroughly cleaned, apply roofing cement with your trowel. Expand the cement 4 to 6 inches past the area of repair. Ensure that you get the cement into the membrane thoroughly until it is fully filled.

Step 5 - Apply Patching Material

With a sharp set of scissors, cut a strip of the roof patching material and place it into the cement. Now apply more roofing cement over the material using a steady pressure so that the cement seats into the material. Smooth the cement out over the outside of the material.

Step 6 - Clean and Seal

After the cement dries, use your alcohol based cleaner to wipe the area thoroughly. Seal the area with roofing tape, applying direct steady pressure to make sure the tape sticks good. Cover the area with gravel.

Step 7 - Check for Leaks

The next best opportunity to check if your repairs were done properly is when the rains come again. Be sure to check thoroughly for leaks in the areas repaired, as well as areas you may have missed. If there are no leaks, you are ready to begin construction on your tile roof.