Sikaflex is the default choice in van conversions and specialist bodywork. Mention sealants in any van build forum and someone recommends it. But Sikaflex covers a wide product family, and the comparison with MS polymer is worth making carefully before your next order.
What Is Sikaflex?
Sikaflex is a range of polyurethane adhesive sealants made by Sika. Different products are formulated for different uses: Sikaflex 221 for general bonding, Sikaflex 252 for structural bonding, Sikaflex 512 for caravan and van applications. The brand is well-established across automotive, marine, and construction.
Most van converters reach for Sikaflex 221 or 512 without questioning it. It works, it's available, and everyone else seems to use it.
What Is MS Polymer?
MS polymer sealants use a modified silicone polymer base instead of polyurethane. The practical differences matter in build contexts. MS polymer stays flexible after cure, bonds without primer on many substrates, and carries no isocyanate risk. It's paintable. It handles temperature cycling without cracking.
Sikaflex vs MS Polymer: The Comparison
Isocyanates: Most Sikaflex products contain isocyanates. MS polymer contains none. For van builders spending long hours in enclosed spaces, this has real health implications and affects your COSHH risk assessment.
Flexibility: Both remain flexible after cure. MS polymer's flexibility is slightly greater, which helps with panels that vibrate and move over time.
Paintability: MS polymer is paintable once skinned. Sikaflex 221 is not reliably paintable — a significant limitation for any joint that gets finished or resprayed over.
Substrate bonding: Both bond to metal, glass, and plastics. MS polymer bonds without primer on more substrates, saving preparation time.
Price: Comparable per tube at retail. MS polymer from specialist suppliers offers better value per unit at workshop volumes.
When to Choose MS Polymer Over Sikaflex
Sikaflex 512 is reasonable for campervan window and roof vent sealing if you're not painting over it. For interior joinery bonding, panel seaming, and any joint that gets painted, MS polymer gives you more control and a cleaner result.
Van conversion workshops building multiple vehicles a month get real advantages from MS polymer's longer working time and paintable cure. Less masking, fewer touch-ups, and no isocyanate exposure during a build that might run for weeks in one space.
Try Mansory — MS Polymer Built for Van Conversions
Mansory is an isocyanate-free MS polymer sealant designed for professional van conversion and specialist bodywork in the UK. Paintable, UV and weather resistant, strong bond on metal and plastic. 310ml cartridge. Workshop packs and trade pricing available.