How To: Additive of the Month – September 2018
WEST SYSTEM® 402 MILLED GLASS FIBRE BLEND (Type: Blended adhesive filler. Product No: 402)
402 is a unique blend of powder and strands.
What is it? WEST SYSTEM 402 Milled Glass Fibre Blend is a mix of individual strands of chopped glass evenly dispersed in a powder base made up of other fillers. This combination creates high-density filler that is perfect for semi-structural repairs. No other manufacturer is produces this type of gap filler and it has proved very effective in GRP repairs.
Used for? Mainly for filling small holes in fibreglass laminates, as any repairs are incredibly strong. A WEST SYSTEM epoxy/402 Filler mix can also be used to build up platforms or other supportive shapes, such as the bulb around a new bow thruster tunnel, or to fill voids under a davit base. The mix can also be used to fill impact damage to centreboards and rudder blades where long-term strength is needed.
Mixing ratio: The WEST SYSTEM 402 Filler should be added at a ratio of 25% by weight to the mixed WEST SYSTEM epoxy. The result will be a thick paste that can be manipulated with a brush, using a stippling motion, or with a palette knife. Repairs can also be held in place with PVC tape or peel ply until they have cured.
Hamish’s Tip’s for the WEST SYSTEM 402 Filler:
Keep it workable.
“The temptation with any epoxy mix is to make enough for the job, but a large amount of filler can exotherm (create its own heat through a chemical reaction) and cure much faster than expected. Only mix up enough material that you can use in 10 minutes or so, and spread it out in the pot of on a roller tray if possible to increase the surface area. This will slow down the exothermic reaction.”
Tidy up with fine filler:
“Because of its mat-like composition, a visible repair may seem a little uneven, so a good tip is to finish off the repair with fine surface filler before overpainting.”
Watch out for needles!
“The thin fibreglass strands that give the additive its strength can also protrude from the cured mix and catch your hands, so we always recommend placing peel ply over the top of the mix as it cures. The peel ply will knock the strands flat and once peeled away will reveal a smooth surface for further build up.”
Typical damage that a mix of WEST SYSTEM epoxy/402 Filler is ideal for mending – by bridging the hole, especially when access from behind the damage is difficult.
The hole is ground back to form a concave receptor.
402 Filler is mixed with added to the mixed WEST SYSTEM epoxy to make a thick paste that seals the gap. Peel ply should ideally be laid over the top as it cures.
Three layers of circular-cut WEST SYSTEM 739 450g/m2 Biaxial Glass Fabric wetted out with WEST SYSTEM epoxy are then added to build up the repair. This process can also be used without the WEST SYSTEM 402 Filler, or instead of.
The repair is then faired with WEST SYSTEM epoxy/409 Microsphere Filler mix. The material is sanded flat when cured.
The final stage is to finish with an epoxy primer and paint system, or a colour-matched gel coat so the repair literally disappears.