A flat roof often leaks due to poor drainage. During a storm, water collects in the low spots on the roof. This is called "ponding." As time goes by, the water seeps through the tar and leaks into the room below. Many times a tar and gravel flat roof will begin to leak near the gutter edge or at flashing. Leaking might also occur around an air conditioning-unit, vents or a skylight. Once leaking does occur, the roof must be repaired. The life expectancy of a tar and gravel roof is approximately 20 years.
Begin with a roofing area that is clean and level. Low spots can cause problems later. The tar product can be spread on with a trowel or mopped on with a regular mop that will be thrown away later.
Work quickly to prevent the tar product from drying out too much. Apply the tar in an area as wide as your roll of felt or tar paper and a just a few feet long. Apply a thin, smooth coat. Once the tar is down, roll out just enough of the felt to cover the tarred area.
Next, move to the next area and repeat the above steps. If your roll of felt is three feet wide, then you will be applying tar to an area approximately 3 feet by 3 feet each time.
Work quickly until you reach the end of the first row. Once you reach the edge of the roof or parapet wall, cut the felt evenly across the end and move back up to the start.
You will repeat this same process for your second and all subsequent rows. Apply thin, smooth coats of tar over the roof surface, the roll out the felt paper little by little until the entire roof surface has been covered.
If there are vents and pipes protruding from the roof top, then it will be necessary to work around those. Use your utility knife to cut the tar paper into the proper shape. Apply tar several inches up the sides of pipes and vents and allow tar paper to fit snugly around them.
It is advisable to use flashing around the edges of any vents or pipes that protrude from the roof surface.
Allow first coat of tar and felt to dry thoroughly before continuing. The second application of tar and felt should be staggered so that it overlaps the seams of the first. This will reduce leakage. In order to accomplish this, you must cut your second row of felt so that it is only half as wide.
If the roll of felt is 3 feet wide, then cut a strip of felt paper 1 1/2 foot wide and the length of the roof area. Once this is accomplished, you can roll the felt up tightly to make it easy to work with. Set the other half of the strip aside for later use.
Work quickly as before, applying thin, even coats of tar, then covering it with the tar paper or felt. As stated above, the seams from the first row should be covered completely by the second row in order to prevent leakage.
Work around vents or other rooftop protrusions as before. Work quickly to prevent the tar product from drying out. Once the second layer has been applied, allow it to dry thoroughly. The tar product should include drying times on the side of the container.
Decide how many layers of tar and tar paper your roof will require. Two may be enough unless you live in a rainy or snowy climate. In areas that receive larger amounts of rain or snowfall, it is recommended that you repeat the above process at least three times before applying the gravel to your final coating of tar.
Once you have applied as many layers of tar and felt as you think are necessary for your rooftop, you can begin the final application.
The final application involves applying the tar as before and then covering it with gravel or some other type of aggregate such as crushed stone.
Begin at your original starting point. Apply tar to a 3 foot by 3 foot area. Broadcast gravel evenly over the tar. Move to your next area and repeat the above process until the entire roof surface has been evenly coated with tar and gravel.
Tar products tend to be easier to work with when warmed; therefore choosing to tar and gravel a roof during the summer months should result in easier application. Try to keep tar product stored in direct sunlight or warmer areas. Commercial applications of tar are normally completed using a machine that keeps the tar at a high temperature.
Tar and gravel roofing must be completed during a time when there will be no rain or other adverse weather conditions. Rain or other moisture must not be allowed on the rooftop until the entire project has been completed. Try to avoid contact with tar product. It will not come out of clothing. If you should get tar on your skin, it can be removed with paint thinner or turpentine.