Neutral versus acetoxy silicones

21.04.2020

In chemical terms, various substances are understood either to be alkaline, neutral, or acidic. Silicones that are used for construction purposes are similarly divided into categories according to the chemicals that are released in the curing process, and are respectively neutral or acetoxy.

Silicones are one of the best-known forms of sealant. They can be utilised for a number of applications due to their elasticity, movement capability in a joint, and high UV and weather resistance. Below we will take a closer look at these two silicone types and their applications.

The smell is not the only difference

Both neutral and acetoxy single component silicones cure due to the presence of air humidity. Although they may have a similar appearance after curing, they have also a number of differences about which one should be aware of before using them, so that the most appropriate product can be selected according to the required application.

For many people, the difference between neutral and acetoxy silicones is simply in the smell. As can be understood by the name, acetoxy silicones that emit acetic acid have a strong vinegar smell during the curing process. Neutral silicones emit compounds that have a specific sweet aroma or are mainly odourless. This depends on whether the curing system is oxime or alkoxy.

The differences between the two groups of silicones is not limited just to odour. Acetoxy silicones are inappropriate for use with uncovered metals because acetic acid evaporates during the curing process and may cause corrosion. Accordingly, it is not recommended to use acetoxy silicones with cement-based products (such as concrete, plastered surfaces, construction blocks, etc) because they will not provide enough adhesion with the surfaces. Neutral silicones provide very good adhesion to the aforementioned materials and therefore they are usable for a significantly wider range of applications.

In which cases should one or the other curing system be preferred?

The simple answer to somebody with limited experience is to use the neutral silicone when in doubt. This relates back to the reasons mentioned above. Discarding special products for specific applications, it could be said that neutral silicones work just as well in places where one would like to use an acetoxy silicone. The same may not be applicable the other way around. Sealing connections between metal surfaces, window sills, ventilation appliances, concrete façade joints, and masonry are just some examples for which a properly applied neutral silicone works correctly, but the acetoxy silicone does not.

It should not be forgotten that for some applications the acetoxy silicones can superbly fulfil expectations and are the proper choice. For example, sealing in sanitary rooms, for which the mainly-used materials include ceramic tiles, glass, and anodised aluminium, the acetoxy silicones fit perfectly and they even provide advantages in terms of costs compared to neutral silicones. One additional advantage of using acetoxy silicones becomes apparent in glass-to-glass joints, for example sealing glass partition walls- acetoxy colourless silicones are significantly more transparent when compared to similar neutral silicones.

In summary, when it comes to selecting the correct silicone, the exact application area and materials which the silicone should adhere to, should kept in mind. More detailed information is available from our silicone’s technical datasheets.