A popular repair on RV EPDM roofs is using coatings, which are supplied by many different manufactures. People think that using coatings to repair your roof is the easiest of all the repairs available. The instructions will start by telling you to thoroughly clean the membrane before you apply the product. Then you will need to measure out the area on the roof to be repaired; for example, you would measure out ten square feet, forty square feet, or one hundred square feet, depending on what you were repairing. They will tell you that one gallon of their product should cover a certain amount of square foot. Lets say, as an example, one gallon covers 100 square feet, .020 mil thick; when you finish applying one gallon, you should be around 100 square feet in coverage. You will use a squeegee or a paint roller to apply their product. So you have applied the product over the area you measured, and your bucket is empty; this means everything worked out as planned, right? Unfortunately, you do not know that for certain. How do you know if you have an equal coating over the entire roof? You could very easily have it thicker in some places than others; some places may have it .040 mil thick while others have only .010 mil thick. Even professionals have trouble being sure the coating is even over the entire roof. This is a major weakness when it comes to installing coatings over an existing roof. Fast forward to five years down the road, when you realize your roof is failing in certain areas. Say you have a warranty and the company asks for a sample; if the sample you send them is only .010 mil thick instead of the specified .020 mil thick, they will tell you that you have applied the coating wrong.

It would seem you are successful because you applied just the right amount of coating for the amount of square feet the instructions told you. But this would not be a true statement, because how would know that you had an equal amount of coating over all of this area? You could very easily have it .040 thick in places and as thin as .010 mill in others. There is no true way to gauge and install the same thickness all over the roof. Even professionals have trouble in making sure that you have met the minimum thickness requirements for the coating products. This is a major weak spot in installing coatings over any existing roof. If you have a warranty problem and they ask for a sample of the failed area and it is only .018 mil thick instead of the specified .020 mil thick they could deny your warranty claim.

This just goes to show you that the "easiest" solution is not always the best solution..