While, unfortunately increasingly rare amongst tradesmen, I find it to be fundamentally sound to properly overlap all building materials so that gravity always carries the water out over the face of the building. There are, however, occasions when that is not practical. One of my regular customers in the historic waterfront district of South Portsmouth has a weather mast at the top of his roof. The weather mast collects data and sends it to a beautiful mahogany display that he created inside the home. The problem is that the rubber boot that seals around the base of the copper weather mast has dried out, cracked, and opened up to begin letting water in the building.
Strict adherence to the principle of properly overlapping building materials would dictate that the weather mast roof boot has to be replaced. We would have to install a new one to seal around the pipe and be overlapped in with the shingles. There is a problem in this case. Unlike a simple pvc vent pipe, we could not simply slide the new boot down over the pipe. So, should we cut the copper pipe and re-solder it after the boot has been installed? Well that’s not a practical solution either. The mast has lots of wiring running down inside of it. Alright, fine, I give up. Let’s just smear a bunch of roof tar over it and call it a day, right? WRONG!
Roof tar has decent adhesion properties, but it dries out and become brittle very quickly with uv exposure. In this case in particular, that would be a big problem. The weather mast moves a fair amount with the wind. The solution must be flexible enough to withstand this and still perform.
So what is the solution? We use a new breed of caulking. It is bad-posterior side. So, we just smear this bad-posterior caulking on the roof boot, right? Negative. The caulking has amazing adhesion, flexibility, and resistance to breaking down with uv exposure. But, it’s only as good as the substrate it’s bonding to. In this case, the substrate (roof boot) is cracked and brittle. The caulking alone would make this 100% better, but still not 100% good. The solution is to smear a layer of the caulking to the roof boot (time to get messy). Then, cut 2 strips of fiberglass mesh cloth to wrap around the boot and the base of the pipe. These cloth strips are well smeared down into the base of caulking, making sure to smear more caulking over the first cloth strip before overlapping the second cloth strip onto it. It is really critical to make sure to smear the cloth in to the caulking completely. Make sure that the caulking and cloth extend from the aluminum portion of the roof boot, over the rubber portion of the boot, and onto the copper pipe with excellent adhesion. Essentially, we’re looking to bridge over and re-inforce the rubber boot. The final steps are to spread a layer of Geocel brushable liquid caulking over the assembly. This can only be done in layers up to 1/32” thick. After a couple of days to allow the first layer to cure, we’ll add a second layer to provide maximum protection.
The time to complete this repair was one hour. The materials cost about $35. Because we’re relying on caulking, etc., we’ll recommend inspecting it every few years and touching up as necessary, but we feel very confident that we just added another life to this roof boot and saved the homeowner a bunch of dough.
By John Bradshaw