Neutral vs. acetoxy silicone: understanding the differences

There are many different types of sealants, and it is not always easy to understand how these products differ from one another and which one to choose for the task at hand. Most commonly, acetoxy or neutral silicone is used for sealing around the building such as in kitchens, bathrooms, windows, facades, and more. They may seem similar at first glance, each has distinct characteristics, applications, and curing processes that sets it apart. Choosing the right type of silicone for your project is essential, as it affects the durability and aesthetic appeal of your sealing work.

Composition and curing mechanism:

The most important distinction between neutral and acetoxy silicone lies in their chemical composition.

• Acetoxy silicone cures in the presence of moisture and releases acid during the curing process. The acetic acid gives the acetoxy silicone its distinctive vinegar-like smell, which can be unpleasant, especially in enclosed spaces. Therefore, additional ventilation is recommended when applying acetoxy silicone. The release of acetic acid helps the silicone to cure faster and form a strong, durable, rubber-like seal.
• Neutral silicone also cures through moisture but does not release any acidic byproducts during the curing process and has a longer curing time compared to acetoxy silicone. In areas with limited ventilation or enclosed spaces, it is preferable to use neutral silicone as it produces little to no odour during curing. It also has a generally lower VOC content than acetoxy silicone, making it a safer choice for indoor applications. Its extended curing time guarantees a meticulous and long-lasting seal.

Compatibility of neutral and acetoxy silicones with materials:

When it comes to compatibility with materials, then neutral silicone has a clear advantage.

• Neutral silicone has excellent compatibility with a wide range of materials without the risk of damaging or discolouring surfaces. It is particularly suitable for sealing sensitive materials such as natural stone, uncovered metals, plastics, concrete and other porous surfaces.
• When extra-strong adhesion with non-porous materials is needed, then acetoxy silicone should be preferred. Acetoxy silicone forms a durable seal with materials such as glass and glazed surfaces, ceramics, covered metals, and other non-porous materials.

Application areas of neutral and acetoxy silicones:

• Neutral silicone is a popular choice for general-purpose sealing works due to its broad compatibility and durability. Its excellent weather-, UV- and ageing-resistant properties make it a reliable choice for both indoor and outdoor projects. It can be used for applications such as sealing around electronic components, mirrors, metal and natural stone surfaces, windows, door frames, glazing, etc.
• Acetoxy silicone is well suited to a range of applications where high moisture resistance, quick curing time and strong adhesion are needed. One of acetoxy silicone’s main advantages becomes apparent when sealing glass-to-glass joints: transparent acetoxy silicone is clearer than similar neutral silicone. Acetoxy silicone is especially well suited to sealing works in bathrooms and kitchens, as it will not become discoloured over time: neutral silicones can sometimes turn yellowish due to the lack of UV light.

In summary, choosing between neutral silicone and acetoxy silicone depends on the specific requirements of your project. While the pricing of silicones can vary based on specific formulation, neutral silicone is typically slightly more expensive than acetoxy silicone. However, when you are unsure about material compatibility, it is always preferable to use neutral silicone, such as Penosil Neutral Sanitary Silicone 350 and Neutral Silicone 317. Neutral silicone guarantees a secure, weatherproof and long-lasting seal without the risk of damaging surfaces.

Acetoxy silicones such as Penosil No Mould Silicone 303 and Sanitary Silicone 313 are recommended for work where quick curing time, cost-efficiency and strong adhesion are important. Acetoxy silicone’s exceptionally strong and durable adhesion with non-porous materials makes it an ideal choice for sealing glass joints and plumbing fixtures, and for making general household repairs.