Last year my wife and I hired someone to replace our home's tar-and-gravel flat roof. The roofer we contacted used a high-tech system consisting of a tar undercoat and a white polymer topcoat. The topcoat was supposed to last longer than a conventional roof, have great insulating qualities, etc. He had a large website with convincing-looking technical explanations.
After a couple of months, the topcoat began to come off. Large areas of it are now missing, and other areas are loose and waiting to detach.
The roofer says the failure occurred because his tar supplier changed the tar's composition without telling him, and the polymer wasn't formulated to stick to it. He claims that all the tar that's available is now this substandard type. (Does that make any sense?) He's refused to give us a refund, claiming he has no money.
Now we're faced with either having another roofer completely remove this roof and start over, or trying to somehow repair the roof we have.
Here's my question: As far as I know, the tar undercoat is fine. (They used a lot of tar; I watched.) Could we just add another coating, or even gravel, to what's there? We could remove the rest of the white topcoat easily enough, if that was important. Structurally, the roof is solid with no sagging areas.
We'd sure like to avoid the expense of a complete new (i.e. torch-on) roof in addition to the money we've already lost. Thanks for your advice!