When a roof leaks, it's not the kind of situation where you can schedule a roofer for sometime next month. It needs to be fixed right now. Because most flat roofs turn into small swimming pools in a good rain, if there is a leak, hundreds of gallons of water may find their way inside, causing an amazing amount of damage. I've had a lot of years to experiment on patching flat roofs, and the patches I applied ten years ago are still good. Here's why.
The primary repair material that I use is called Henry's Wet Patch. It's a sticky, black, tarlike substance that can be applied to wet surfaces -- even underwater. But my secret ingredient is aluminum foil, and an assistant to help me apply it. Several garbage bags, some duct tape and a disposable spatula are also required ingredients.
If you try this, you'll get the Wet Patch on your hands and arms, so protect them with the garbage bags. Hold them in place with the duct tape. Scoop the Wet Patch with the spatula and spread it over the hole. Have your helper tear off a piece of aluminum foil that will almost cover the Wet Patch. Press the aluminum foil into the Wet Patch with your covered hand and use the spatula to press its edges into the Wet Patch. That's all there is to it. When you are done, peel off the garbage bags, and stuff all the trash into them.
This kind of patch lasts a lot longer than a simple gob of Wet Patch spread over a hole in the roof. My theory is that the Wet Patch seals the leak and that the foil prevents the Wet Patch from outgassing, drying out and ultimately cracking. It doesn't make for a pretty patch, but it's quick and will last for many years -- plenty of time to schedule a new roof.
Kee Nethery, Berkeley, CA
From Fine Homebuilding 133, pp. 34
September 1, 2000