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Text: Kaia Koitmäe, product manager, Monika Kelle, Wolf Groupi brand manager
Every builder knows the frustration of silicone that won’t adhere to the substrate, turns yellow or releases a strong smell during application. Neutral silicones solve many of these headaches, offering excellent adhesion, flexibility, and a smoother curing process. But with so many options – MEKO and MEKO-free oximes, alkoxies, and beyond – how do you pick the right one for the job?
A few types of silicones are used in construction, but the two most important are neutral and acid-cure silicones. For many people, the difference between neutral and acetoxy silicone is simply in the smell. Neutral cure silicones emit very little odour, making them ideal for indoor applications, whereas acid-cure silicones have a stronger vinegar-like smell. However, there are more properties to consider and requirements to fulfil when choosing the right type of silicone, such as mechanical properties, product stability, the emission of volatile organic compounds (VOC), etc. When in doubt about which curing system to use prefer neutral silicones.
What is special about oximes?
Neutral silicones can be divided by oximes, alkoxies and benzamides. Oximes can be either MEKO or MEKO-free. MEKO oximes have all the best properties of neutral silicones. They are highly durable, cure quickly, adhere to most substrates, are non-corrosive with metals and cementitious products and are reasonably priced. The disadvantage of MEKO oximes is that they emit oxime compounds during the curing process, therefore they do not comply with low VOC requirements and are meant for use in ventilated areas.
Advanced MEKO-free formulas are not harmful to your health and the environment. MEKO-free silicones are versatile, odorless, non-hazardous and compile low VOC requirements, EC1+, and French A+.
Wolf Group has a vast portfolio of oximes: Neutral, Universal, Neutral 12,5E, Neutral 25LM, Neutral Glazing, Seal&Bond silicones. Neutral oxime silicone formulations can be successfully used as multi-purpose products due to their unique combination of properties. The specialities include Fireproofing, High Temperature and Natural Stone 25HM silicones. Whether you are looking for a filled or unfilled version, MEKO or MEKO-free product- we´ve got you covered.
Fans of alkoxies
Alkoxies also belong to the neutral silicones class and have dedicated fans. In some markets with strong building traditions, It is common to prefer a highly durable, yet a bit pricier neutral silicone curing system. Alkoxies emit alcohols during the curing process, usually ethanol or methanol, however, the product is almost odorless, compiles low VOC requirements, meets EC1+ and French A+ standards. It is suitable for both porous and non-porous surfaces.
Get exactly what you need
Builders often rely on products they have used for years, remaining unaware of various curing systems and new-generation silicones. However, with countless brands and formulations available, selecting the right one can often feel like navigating a construction labyrinth. Trust reputable producers whose product labels provide information about chemical composition, substrates, application areas and more.
Although 100% silicone is available for industrial and professional glazing applications where additives may harm surrounding sensitive materials, it is common that silicones contain different additives, e-c chalk and talc to improve the characteristics of the formula.
Step 1: identify the curing system that is suitable for the substrate
Step 2: identify the curing system that is suitable for your application area
Step 3: evaluate the other requirements and conditions required for your project: indoor or outdoor use, paintability, mould resistance, etc.
Your cheat sheet
Numerous neutral multipurpose silicones can be used for various sealing, fixing and repairing applications. Builders usually evaluate the product through its viscosity and speed of squeezing out of the cartridge, but there are more to take into account, for example, product density, loss of volume and CE-marking.
- If you need a silicone that has equally good adhering and sealing properties for indoor and outdoor applications, choose Seal&Bond type multipurpose silicone.
Density 1,38 g/ml (DIN 53 479-B)
Loss of volume <10%.
CE-marking:
EN 15651-1 F-EXT-INT: 12.5P – transparent
EN 15651-1 F-EXT-INT: 7.5P – colours
EN 15651-3 S: S2
- If you need silicone with good mould and moisture resistance, choose Neutral Silicone 12.5E. It can be used indoors and outdoors for weathersealing, glazing, ventilation and sanitary works.
Density 1,42 g/ml (DIN 53 479-B)
Loss of volume <20%
CE-marking:
EN 15651-1 F-EXT-INT: 12.5E
EN 15651-2 G-CC
EN 15651-3 S: S1 – unfilled
EN 15651-3 S: XS1 – filled
- If you need a product with low modulus, high elasticity and high movement capability (±25%) for expansion joints, glazing and weathersealing, Neutral Silicone 25LM is the ideal choice. NB! The term modulus refers to a material’s flexibility or rigidity, specifically, the resistance of a substance to deformation due to external forces. Low-modulus (LM) silicone offers less resistance than a high-modulus (HM) silicone sealant. Therefore LM is preferred in high moving joints such as window frames or expansion joints.
Density 1,01 g/ml (DIN 53 479-B)
Loss of volume <10%.
CE-marking:
EN 15651-1 F-EXT-INT-CC: 25LM
EN 15651-2 G-CC: 25LM
EN 15651-3 S: XS1
- If you need a silicone that adheres to most materials and has a long service life for sealing curtain walls, facades, window and door systems as well as window and door installation, choose Neutral Weathersealing & Glazing Silicone.
Density 1,02 g/ml (DIN 53 479-B)
Loss of volume <5%
CE-marking:
EN 15651-1 F-EXT-INT-CC: 25LM
EN 15651-2 G-CC: 25LM
- If you need high-elasticity silicone for glazing works, perimeter weathersealing of windows and doors, curtain wall sealing, sanitary and ventilation works, choose Alcoxy silicone 25LM.
Density 1,02 g/ml (DIN 53 479-B)
Loss of volume <10%
CE-marking:
EN 15651-1 F-EXT-INT-CC: 25LM
EN 15651-2 G-CC: 25LM
EN 15651-3 S: S1 (fungicide version)
Importance of UV light
All silicones are ultraviolet (UV) resistant due to their chemical formulation. But have you ever thought that some silicone formulations require UV light? Oxime silicones resist degradation from ultraviolet light, making them ideal for outdoor use. Neutral silicones are ideal in glazing and other outdoor applications that have direct sun exposure. Conversely, a lack of UV light encourages yellowing in most neutral curing silicones. The less UV light available, especially during the curing phase, the more likely and severe the yellowing can be. Transparent silicone is the most prone to yellowing and therefore neutral cure silicones are not recommended for dark windowless rooms (e.g. toilet or bathroom). The best solution for such rooms is acetoxy silicone. By the way, if a yellowed silicone joint gets UV exposure, it restores its normal colour.
