Why Is Your Silicone Peeling Or Cracking? 5 Common Causes Of Sealant Failure

Key Takeaways

• UV degradation is the leading cause of outdoor sealant failure in Australia. It causes cheap silicones to go brittle and crack.
• Mould growth usually happens because the wrong sealant was used in a high-moisture area.
• Poor surface preparation prevents a proper bond. You must completely remove old residue before applying new silicone.
• Neutral cure silicones are required for sensitive materials to prevent corrosion. 

Noticing a leak under the kitchen sink or seeing black spots in your shower corners is a sign that your sealant has reached the end of its life. In the harsh Australian climate, even high-quality products face extreme stress from UV radiation and temperature swings. When a seal fails, it doesn’t just look bad. It can lead to structural water damage that costs thousands to repair.

This guide identifies the primary reasons for sealant failure and explains how to choose a more durable silicone sealant for your next repair. 

1. UV Exposure And Weathering In The Australian Sun

Australia has some of the highest UV levels in the world. Standard or “budget” sealants often lack the stabilisers needed to survive direct sunlight. Over time, the sun breaks down the chemical bonds in the silicone. This leads to shrinking, chalking, and eventually deep cracks that let water through.

How To Fix It

For any exterior application like windows, roofs, or doors, you need a high-quality product like Roof & Gutter. It is a low modulus, neutral cure silicone that stays flexible. It is specifically formulated for high UV resistance. It won’t go brittle after a single summer.

2. Mould Growth And Moisture Retention

Black spots on your sealant aren’t just a cleaning issue. They are often a sign of product failure. Standard silicones can become porous over time, which allows moisture and soap scum to sit on the surface. This creates the perfect environment for mould to grow behind and through the bead.

How To Fix It

In bathrooms and kitchens, you must use a sanitary grade silicone. Bathroom & Kitchen Silicone contains powerful fungicide protection that helps prevent mould and mildew growth even in high-humidity areas. Plus, ensure your bathroom has proper ventilation to help the surface dry out between uses. 

3. Poor Surface Preparation and Old Residue

If your new sealant is peeling away in long strips shortly after application, the cause is almost always poor preparation. Silicone does not stick to old silicone. Even a tiny amount of residue or “silicone oil” left on the tile or glass will prevent the new bead from bonding.

How To Fix It

You must mechanically remove the old sealant with a scraper. Then, use a dedicated cleaner or a solvent like methylated spirits to strip away any remaining oils. The surface must be 100% dry and dust-free before you start. If you are bonding larger components during a renovation, remember to choose the right adhesive to support the sealant’s job.

4. Using The Wrong Type Of Sealant For The Material

Many people don’t realise there’s a big difference between acetoxy (acid cure) and neutral cure silicones. Acetoxy silicones have a strong vinegar smell and can cause corrosion on metals like stainless steel or aluminium. They can also react poorly with alkaline surfaces like concrete or natural stone, leading to a loss of adhesion.

How To Fix It

For most construction materials, a neutral cure silicone is the safest bet. It has excellent primerless adhesion on a wide range of surfaces, including sensitive metals and masonry. It won’t cause the staining or corrosion that cheaper acid-cure products might.

5. Joint Movement Exceeding Product Limits

Building materials expand and contract as temperatures change. If a joint is too narrow or the sealant isn’t flexible enough, the bead will either tear down the middle or pull away from the edges. Cheap fillers often have very low movement capacity, meaning they can’t handle the “stretch” required for Australian homes.

How To Fix It

Check the movement capability on the technical data sheet. Professional products in the Soudal Silicone Sealant Range typically offer much higher elasticity than budget alternatives. This allows the seal to stay intact even as the building moves.

Best Practices: Preventing Future Sealant Failure

Getting a long-lasting seal requires the right technique as much as the right product. Here is how our team recommends approaching your next job.

• Strip it back: Never apply new silicone over old. It will fail. Remove every trace of the old product first.
• Size the joint correctly: A joint that is too thin will fail because it can’t stretch. Aim for a minimum depth of 5 mm for most household seals.
• Tool it properly: Use a profiling tool and a soapy water solution to smooth the bead. This forces the silicone into the edges of the joint for a better bond.
• Check the cure time: Most silicones need 24 hours before they can be exposed to water. Don’t use the shower too early.

Stop Repairs From Becoming Re-dos

Sealant failure is frustrating, but it is usually avoidable. By understanding the stressors of your environment and selecting a product like the Soudal Silicone Sealant Range, you can ensure your home stays watertight and mould-free for years.

To find the right sealant for your specific project, browse our full range of silicones or view our technical application guides for more expert advice. You can also find your nearest Soudal stockist today.

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