When it comes to sealants, silicone is the trusty Swiss Army knife of the construction world – durable, flexible, and ready to take on whatever weather throws its way. But not all silicones are created equal, so how do you choose the right one without getting stuck (pun intended)? Here’s a guide to help you pick the best silicone for your job and avoid sealing your fate with the wrong product.
1. Understanding Silicone Types
First things first, let’s break down the two main types of silicone sealants: neutral cure and acetoxy cure. Each type has its quirks, so knowing the difference is key:
Neutral Cure Silicone Sealant
These are your go-to for expansion joints. They cure without releasing acetic acid, making them friendly with sensitive materials like concrete, PVC, and metals. They’re also great at sticking to aluminium and glass.
Pro tip: If you’re sealing PVC or aluminium window frames, neutral silicone is the safe bet. Unless you’re into surprises like cracked seals, stick with the neutral option.
Acetoxy Cure Silicone Sealant
These cure faster and bond well to non-porous surfaces like glass and aluminium. However, they release acetic acid during curing – that’s the vinegary smell you’ll love to hate. They can corrode certain metals and don’t play nice with some plastics.
Pro tip: Use these for glazing jobs but steer clear of copper and lead unless you want to create your own science experiment.
2. Low Modulus Neutral (LMN) Silicone Sealant
If flexibility is what you’re after, LMN silicones are your best bet. These highly elastic sealants are perfect for areas prone to movement, such as façades and glazing joints. Think of them as the yoga masters of sealants – flexible, reliable, and always ready to bend without breaking.
Here’s what to consider when comparing LMN silicones:
Loss of Volume: Premium LMN silicones shrink less after curing, which means your seal stays solid for the long haul.
Elasticity: Higher elasticity ratings mean better movement accommodation. If you’re sealing something that moves a lot, choose a silicone with a high movement class.
Viscosity and Density: A silicone with fewer solvents has a “fuller body” and better extrusion control. Beware of products with fillers that make the silicone look fuller but increase shrinkage over time – the seal might end up flatter than your post-Christmas diet plans.
3. CE Markings and Declarations of Performance (DoP)
CE marking is more than just a fancy label; it’s a sign that a product meets rigorous European safety, health, and environmental standards. Introduced under the Construction Products Regulation (CPR) in 2013, CE marking replaced the older Construction Products Directive (CPD) to ensure uniformity across EU member states. Unlike the CPD, the CPR is directly binding, leaving no room for local adaptations or delays.
The CPR mandates that every construction product with a CE mark must be accompanied by a Declaration of Performance (DoP), which outlines the essential characteristics of the product. Manufacturers are required to provide this DoP either digitally or on paper, and it must be retained for up to 10 years. So, when you buy a CE-marked silicone, you’re not just getting a product; you’re getting a performance guarantee.
Here’s what CE markings tell you:
EN 15651-1: For façade elements (e.g., concrete, aluminium)
EN 15651-2: For glazing (e.g., glass)
EN 15651-3: For sanitary joints (e.g., bathrooms)
EN 15651-4: For pedestrian walkways (e.g., flooring joints)
The product’s Declaration of Performance (DoP) summarises the test results. Key bits to look for, as specified by the CPR, include:
Resistance to Flow: Higher numbers mean better extrusion control.
Loss of Volume: Lower is better – less shrinkage means a more durable seal.
Elastic Recovery: Higher numbers indicate greater elasticity and longer-lasting performance.
Remember: A good DoP can be the difference between a seal that lasts years and one that calls it quits before the paint dries.
4. Visual Example of a CE Marking
The image below shows a sample CE marking for a Soudal silicone product. Let's break down what it represents:
EN 15651-1: This indicates that the product is suitable for façades, both internal and external (denoted by F-EXT-INT), and has a movement accommodation of 25% (25LM).
EN 15651-2: This denotes suitability for glazing applications (G-CC) with the same movement class of 25LM.
DoP Number: Each CE-marked product must have a unique Declaration of Performance (DoP) reference number, which allows the user to access the full technical specification provided by the manufacturer.
NB Number: The notified body (NB) responsible for assessing and certifying the product is identified by this code (NB0757).
CE markings are only useful if you understand what they mean. They’re more than just labels—they ensure your product meets strict safety and performance standards. Knowing how to read them, like recognising EN 15651 codes for façades or glazing, helps you choose the right product for the job. Without this knowledge, the label is just a meaningless stamp.
5. The MEKO Content Concern
When selecting a silicone sealant, it’s essential to consider safety factors, such as the presence of MEKO (Methyl Ethyl Ketoxime). MEKO is a by-product released during the curing process of some neutral-cure silicones and has been classified as potentially carcinogenic (H351 – suspected of causing cancer). This health concern is particularly relevant for indoor applications or poorly ventilated areas where users may be exposed to curing fumes.
At The Plastics Shed, we prioritise customer safety, which is why we do not stock or sell any silicones containing MEKO. All our silicone sealants are MEKO-free, ensuring a safer option for both professional users and DIY enthusiasts. By choosing MEKO-free products, you reduce the health risks while still achieving excellent sealing performance.
This label ensures that the product has been tested and complies with the relevant European standards, giving DIYers peace of mind that they’re using a reliable product.
For DIYers, understanding which products require CE marking can be crucial. For example, sealants used for façades, glazing, sanitary joints, and pedestrian walkways must carry the CE mark, while products like primers, cleaners, tapes, and non-construction adhesives do not.
Choosing the right silicone isn’t rocket science, but knowing the regulations and performance standards helps you avoid costly mistakes. Stick with these tips, and you’ll seal your projects with confidence.
Happy sealing!
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