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Top tips for easy sanding with WEST SYSTEM epoxy

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Are you about to start fairing a hull? It may seem like a daunting task but there are ways of making the process run more smoothly – and achieve a great smooth finish. Before using fairing boards for final faring, why not try working with a grinding device? It will remove a substantial amount of material very quickly but will need a bit of careful handling to control that removal.

Prepare your sander
Start off by gluing a 9″ × 11″ rectangular piece of fibreglass onto the standard round foam backup pad on your 0 to 6,000 rpm sander/polisher. This will make it virtually impossible to gouge the surface. This soft foam is used on concave surfaces.  If you’re unsure where to get a fibreglass ‘rectangle’, try an industrial supplier or make your own by laminating three layers of a double bias 450g/m2 biaxial fibreglass sandwiched between single layers of 200g/m2 woven cloth and unthickened WEST SYSTEM® epoxy.

It’s probably a good idea at this stage to cut the corners of the square pad to a radius of 50mm and sand all the edges for safety. Your sander should look something like this:

Draw ‘glue’ and ‘sight’ lines
Be sure to attach the foam to the exact centre to avoid  distortions. To do this,  mark the centre with a centre punch and mark a circle the exact size of the pad’s diameter with pencil compass or scriber. This is the glue line. Then make a concentric ring 3mm  larger. This is the sight line – you’ll need this because once the epoxy starts to squeeze out, you won’t be able to see the glue line easily. Finally, ensure both surfaces have been abraded with sandpaper.

Apply epoxy to each surface
Apply two thin, level coats of unthickened WEST SYSTEM epoxy on each surface, ensuring that the surface under the square is flat.  Your clamping system should be simply four 25mm x 100mm boards about 300mm long and 2kg lead weights.  This passive clamping protects the foam from permanent distortion. Remember: never store the pad on its face with the machine attached. Doing so will distort the foam and render it useless!

Top operational tips

1. The optimum speed seems to be about 3,000 rpm. If you’re using a variable speed machine, slower speeds will help to you gain confidence. It can be bit scary to have the rectangle zinging around very fast! 

2. Constant diagonal movement across the surface is essential. Never move in a fore and aft direction on a waterline.

3. Move your feet 3″ to 4″ for every pair of arm passes. Areas that require kneeling or reaching out still need this constant motion. (Likely to be a bit uncomfortable – sorry about that!)

4. Multiple passes removing small amounts of material on each pass is the best approach. As the job progresses, the visible irregularities will disappear. Dust off the hull many times during this stage and inspect it thoroughly.

5. Using the flat of a pencil, mark any imperfections. In addition to marking trouble spots, make multiple S-shaped scrawls on the whole surface to keep track of where you’ve been.

So, there are our sanding tricks of the trade. Have a go next time you’re about to start fairing your hull. It might make the job a little easier. Still not sure? Head over to West System International for more tips on fairing.

Our thanks to Damian McLaughlin for his great ideas.

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