Pros and Cons to Mastic Sealant

A mastic sealant is a type of liquid sealant that cures in an elastic state thus making it flexible yet still keeps the bond of the surfaces that is attached together. It adheres to just about any material making an all around type of sealant. Wood, aluminum, glass, marble and even duct board are the types of material that mastic sealant is used on. Most contractors use mastic sealant to connect windows to structures. Cracks around bathtubs can be sealed with mastic sealant and other types of masonry as well. Roofing and brick structures work well with mastic sealants and even vehicles such as cars and boats also take mastic sealants to create a dust free surface. The life of mastic sealants is usually about 5 years before reapplication to ensure its efficiency.


  • The good quality of mastic sealant is that is has a very smooth exterior while keeping its rigid form underneath.
  • Surfaces do not have to be primed when using this type of sealant, and although applied thick, it will go on smoothly on any surface. It is important that the area to be joined or sealed should be clean and dry, just like any other sealant in the market.
  • Mastic sealant may be used outdoors as well because of its waterproof quality. It can be applied on rain duct leaks for outdoors.
  • It is also favored for areas to be applied that will under high or low temperatures such as heater vents or drier vents and contains ultraviolet inhibitors to make sure that it is protected from damaging effect of the sun that will often weaken other types of sealants that is why it is best to use it on roofs or any surface that is constantly exposed to sunlight. Most sealants will also not work well with metal because it will not corrode it over time.
  • Also, because of the mastic sealant’s flexible quality, it is best to be applied in adjoining areas with high vibration and heat like heater ducts. These vibrations cause the joints to move and eventually disconnect and that is the sealant needs to be flexible.


  • The not so good quality of mastic sealant is that is not recommended to be applied to areas that have too much joint movement or anything that will be moved at a long length although it is a type of flexible sealant.
  • It only works well with constant pressure on it but not constant movement.
  • It also works best when applied thickly and it not recommended if only a thin layer is needed such as touch ups and what not. One should simply resort to other types of sealant.