How To: Sheathing with epoxy: your only choice of resin
David Johnson, West System International technical expert, explains why epoxy should be the only resin system you reach for if you’re looking to effectively sheath your deck or hull.
The benefits of sheathing the key structural elements of a boat come down to one word: durability. By using glass cloth and the adhesive qualities of epoxy to laminate and protect your vessel, you increase water resistance, you make the craft stronger and you guard against wear and tear and abrasions. In short, you make your boat more durable.
But to create the highest level of durability, you have to use epoxy in combination with the very best glass cloth. You can achieve this by using a lightweight woven material such as one of the Glass Fabrics or, for boats larger than 18ft or on projects where strength is your biggest concern, biaxial fabric made from two layers of unidirectional fibres, such as Biaxial Fabric.
Use these materials and you’re working with the strongest system and the most resilient cloth available. Or, to put it another way, you’re setting yourself up to succeed.
The problem with polyester
Not too long ago, boat builders who wanted to sheath their craft would often reach for polyester resin and chopped strand mat. Thankfully, that’s becoming increasingly rare.
Polyester lacks the adhesive resilience you need to reliably bond to the underlying substrate – whether that’s wood, metal or an advanced composite. Also, the short length of fibres in chopped strand mat means strength is compromised there too. Introduce materials like this to harsh marine environments and you risk seriously limiting the lifespan of your vessel.
Instead, the epoxy I’d always recommend is WEST SYSTEM 105 Epoxy Resin®. This should be used with WEST SYSTEM 205 Hardener® or, where a clear coated finish is required, the WEST SYSTEM 207 Special Coating Hardener® or, for larger surface areas where you need more working time, 206 Hardener®.
All of these products are specifically designed for marine use and applied effectively, they create protection that lasts for decades. Boats I worked on using WEST SYSTEM® epoxy in the 1970s still have a pristine epoxy/glass sheathing today.
Preparing to succeed
Whether you’re sheathing a brand new glass composite boat or repairing a historic wooden hull, the process for sheathing remains the same.
Clearly if you’re repairing an old vessel that’s been damaged in the water, it’s vital to ensure everything is thoroughly dried out before you begin work.
But the other key thing to remember – whatever you’re sheathing – is to ensure you scrupulously wet out the fabric and then carefully remove all air bubbles – ideally using plastic squeegees and foam or paddle rollers.
Take the time to complete the process carefully using the best available materials and you’ll create a powerful barrier to future water absorption and damage that will last for many years.
Got a boat-related technical question you’d like David to blog about? Then do get in touch.