Torch down modified bitumen over silicone sealant coated section of roof

I have a small section of flat roof that was coated with 100% Henry silicone over the modified bitumen. I want to install another layer of torch-down bitumen to the whole roof, including the small section with the silicone coating. In order to make the bitumen stick to the silicone coating area, I was advised by someone to coat another layer of silicone, then spread coarse sand on it. Once dried, you can put another layer of torch-down bitumen on it. Has anyone tried this method?

Nail base sheet over it, then apply your cap sheet.


The only method I’ve tried that has worked to remove silicone from mod-bit is heating it with a torch. If there’s enough moisture under it, it will blister and get aggressive with a street broom and you might get lucky. Caveat, Just say NO to silicone…

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Which is the best and most durable modified bitumen brand and thickness?

Typical qualify torch down products will be 160 mils for cap sheet.

There isn’t a huge difference between the major brands. I prefer Firestone, which recently changed to Holcim Elevate, or Soprema. But JM, and GAF are also good brands. Certainteed sells cap also but I don’t have much experience with it.

For your silicone, the only real answer is you can’t go over it directly. As rooferama said, mechanically fasten a base sheet over it. If it is a small spot you can get silicone up with kerosene and a lot of elbow grease, but it takes forever even for a small spot and you have to be careful not to damage the roof underneath with the solvents.

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SBS is more flexible and works better in cold climates and is usually mopped or cold processed. APP is torched down. Ultimately is quality is incumbent upon the applicator. I’ve repaired a lot of them and have seen where the only torch work was on the seams. If there is moisture in the system, it needs to be vented or torn off.

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That is very interesting.
Im not
Going to put it down.
I like the idea.especially for a small flat area.
But i wouldnt trust anyone else but myself.

I have been successful( about 5 years so far)
On one project.
I installed asphalt primer from a 5 gallon bucket on top of the silicone.
About 30 hours later i installed self adhered modified bitumen with a small amount of heat from my torch.
I fully expect it will last over its intended warranted life and not blow off.

I did it this way because the silicone was on top of a tapered system and i didnt want to put crazy long screws through everything.
Im happy with the results so far.