Tar and gravel roofs are made of layers of material glued together with hot asphalt. A coating of hot asphalt is applied on top, with gravel applied before the hot asphalt cools. If you find visible damage (separation, a tear, deterioration) you can see what needs to be repaired. However, after removing the loose gravel at the leak area, it is most common to see no visible indication of a leak, since you cannot see water seeping through the membrane. In these cases, the adhesive “hot asphalt” has failed. As well, water can travel from other locations, sometimes up to dozens of feet away.
If the proper material is applied in the right area in the right way, the leak will not come back. The question is, “How much area should be sealed?” It is an educated guesstimate, especially in the case of a traveling leak. If, after repairs are completed and the leak shows up again, examine the area previously repaired. If the repair is sound, the problem area is larger than originally thought and an estimate for the cost to coat a larger area is provided, as more repairs are needed. In the case of an old tar and gravel roof that has reached the end of its useful life, there are other types of materials that can be installed for new flat roofs.