In today’s post, Roofer’s Guild provides a basic overview of roof mastic and how to use it. We will also be going over some of the pros and cons of this roofing solution.
Table of Contents
What is Roof Mastic?
Roof mastic is a material used to seal vulnerable parts of a roof. In essence, it is a sealant but a more specialized kind of sealant. For example, it is thicker than seam tape and provides harder protection against leaks.
Roof mastic shores up the defenses of commercial flat and metal roofs. You may have heard them referred to by other names like mastic coatings or roof repair mastic, but they are all the same.
Some will mistakenly refer to them as simple roof sealants, but this is a misnomer. While mastic is a type of roof sealant, not all sealants are mastic.
Roof Mastic Characteristics
Thickness is the foremost characteristic of roof mastic. It has a very high viscosity, making it practical for patching vulnerable parts of a flat or metal roof. In addition, the thick layer forms a tight seal around the roof opening that does an outstanding job of keeping moisture out.
Roof mastics are highly flexible, making them useful on various roof coatings. One of mastics’ primary benefits is it stands up to thermal expansion and contraction due to its thickness and flexibility.
The roof system allows thermal shifting without damaging the substrate or cracking. As a result, roof mastic is an excellent choice to seal roofs in regions with wide temperature fluctuations.
You can apply mastic sealant to asphalt, spray polyurethane foam, built-up roofs, metal, EPDM, and many other common types of commercial roofing systems.
What is the Purpose of Roof Mastic?
Roof mastic aims to shore up vulnerable parts of a commercial or industrial roof and prevent leaks. Roofers typically apply them wherever there is a break in the roofline, as in seams, drains, vents, skylights, and chimneys.
Since it is so dense, contractors also use it on vertical and pitched surfaces.
Roof mastics are also commonly applied to metal roofing, where the sealant has to be a bit more intricate. The thickness of the material is ideal for water-proofing commercial and industrial roofs and typically works in conjunction with some roof coating systems.
Many roof mastics are applied right after a new roof coating system has been fully cured.
It’s also important to note that roof mastic is not a roof repair material – in contrast to the traditional sealant. Instead, contractors install roof mastics, usually in conjunction with a complete roof coating system.
In rare cases, it may be suitable to use a roof mastic material to perform a roofing repair or to shore up a leak. In general, these materials are applied while installing a new commercial roofing system.
Types of Mastic Material
Depending on your manufacturer, you will have different options for the mastic material. In general, you can choose acrylic, butyl, silicone, or urethane mastic material.
- Acrylic
- Butyl
- Silicone
- Urethane
The best option depends on which roofing system you are installing or, in some cases, repairing.
Pros and Cons of Roof Mastic
At this point, you may be thinking, “Roofing mastic sounds great!” and you’re not entirely wrong. But just like with any roof sealing solution, it, too, comes with its fair share of ups and downs.
Take a look at some of the main selling points and drawbacks:
Pros:
- Mastic cures very smoothly, so it looks pleasing when it dries. It also finishes very uniformly, which lends an almost aesthetic look compared to other roof sealing solutions.
- Roofing mastic requires little priming as well. Just make sure you fully cure the roof coating, but other than that, the mastic application process requires little prep work.
- It essentially cures as an elastic material, meaning that it is very flexible even after curing. This characteristic makes it hold up to thermal fluctuations so well and makes it viable in many different types of roofing systems.
- Roofers can use roofing mastic on heating ducts and other roof parts that are subject to constant vibration. Because it is so flexible, it doesn’t shift when the substrate or immediate area moves or vibrates.
- Roofers can also apply the material in various ways, including caulking guns, rollers, brushes, trowels, and more.
Cons:
- Contractors must apply it in thick coats, which can sometimes drive up the cost of both materials and labor.
- Since roofing mastic is so naturally thick, it cannot be applied using a traditional hydraulic sprayer.
- While roofing mastic is flexible and durable, it’s not a miracle worker. The mastic material may fail if the roofing system is prone to extreme shifting.
- The application process can be very time-consuming if you use a caulking gun, trowel, or brush. The labor can also be intensive if you are working to seal a large roof.
It would be best to discuss the merits and drawbacks of roof mastic with your customer and carefully calculate the installation cost for yourself. Laying out the pros and cons is the best way to ensure the project’s timely completion.Ultimately, we hope this post helps you better understand roof mastic.
