Hot-mopping a roof

Hot-mopped roofs are durable, low-cost options compared with other types of roofs. They are designed for roofs with shallow pitches that rise no more than four inches every foot. A built-up hot-mop roof consists of various layers of felt and asphalt over a bed of rosin paper. Flashing is used around the roof features as is required. Reflective gravel or cap sheet limits sun damage and improves the roof’s appearance. The fumes released by liquefying the asphalt cause smog production and due to this factor, hot-mopping may not be allowed in all jurisdictions and it may only be allowed during certain times of the year. Hot-mopping works well with older mobile homes and larger industrial buildings that do not have a high-pitched roof. Your local roofer in Austin will be able to answer your questions concerning hot-mopping.

You will need the following items:

  • rosin paper

  • cant strips

  • roofing nails and hammer/nail gun

Follow these simple instructions to hot-mop your roof:

You want to nail the cant strips at 45 degree angles at all inside corners, a foot or 12 inches on center using a hammer or nail gun and roofing nails. This includes all roof corners and roof features with interior corners such as chimneys, curbs and parapets.

Using a staple gun to layer the rosin paper lengthwise over the roof and cant strips. If short-handed, staple one end of the paper and then stretch it out to the other side of the roof. Then staple that end before adding more staples along the seam.

Layer and nail base sheets shingle style over the rosin paper making sure that there is a two inch overlap between the courses.

Cut and install flashing as needed around roof fixtures and penetrations. Then set flashing in plastic roofing cement to reduce leakage and spray with asphalt primer.

Pour the hot asphalt from the asphalt kettle into a bucket or pump for larger roofs. Transport the bucket or pump to the roof. Remember to practice safety first and remind others that are working with you that you have a ‘hot’ item when you move it around the roof. Molten asphalt has an extreme danger for serious injuries if splashed or spilled.

Use a fabric roofing mop to lay up the roof from lower elevation to high. Apply the asphalt to the base sheet and then building felt, then asphalt. Repeat this process for three layers or four if you are counting the base sheet. The felt should be staggered similarly to the base sheet application, shingle style, using two-thirds coverage.

Then you want to sprinkle light colored gravel evenly over the final hot-mopped layer of felt to limit UV damage. You may used an aggregate-infused cap sheet instead of gravel to reduce the overall weight.

If these instructions are a bit daunting to you, you can always call on a professional roofer in Austin to do the roof for you. Your local roofer in Austin will be happy to come out and give you a solid estimate to hot-mop your roof.

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