Machine polishing fibreglass
Compare orbital vs rotary polishers
Orbital polisher
- Best for polishing and buffing
- Covers large areas very fast
- Won't overheat gel coat or leave 'comet tails'
Rotary sander-polisher
- Multi-purpose machine
- Great for repairs and preparation
- High speed must be used with care
Rotary sander-polishers are general-purpose machines, well suited to repair work, sanding, heavy-duty preparation and compounding. Orbital polishers are quicker for finish polishing as they have a larger head and can't overheat the surface.
Using an Orbital Polisher
An efficient orbital polisher gives the fastest brilliant finish on gel coat. It can buff the topsides of a boat in minutes, and makes it practical to maintain a brilliant shine on larger vessels. The hand-like action is easily controlled, can't damage the surface and won't run away from the operator.
If you have a choice of bonnets, use the cotton one for Pre-wax shine restorer. Apply it directly to the bonnet, and place the machine in contact with the surface before switching on. Keep firm pressure and work rapidly over the surface. Clean off any residue before waxing.
Wax can be applied by hand to the surface and the lambs wool bonnet used to shine it. Again start the machine with the pad in contact with the surface. Do not coat the bonnet with excessive wax, as this is wasteful and slows down the process.
Using a sander-polisher on fibreglass
Fibreglass gel coat is easily damaged by overheating, so speed must be controlled and the machine must be used with care. Here are some top tips from experts:
- Don't use the disc edge - it can dig in
- Use a low speed for compounding and polishing
- Reduce pressure as you increase speed and watch out for overheating
- Use foam pads for compounding and polishing
- Swap to a small head for detail work
Sanding is normally used to clean up repairs or to correct very bad surfaces. When sanding, work down through progressively finer grades to remove scratches, ending with 400 grit before going on to compounding. Sanding can be done at higher speed than buffing.
Compounding is for removing scratches and abrasion damage. Like sanding, the process removes material from the gel coat, so it shouldn't be used on a routine basis for restoring shine. Don't attempt to buff out sander scratches coarser than 600 grit.
Before compounding, make sure the surface is thoroughly de-waxed. Traces of wax cause the compound to cut unevenly, giving a patchy result that is particularly noticeable on coloured gel coat. Boatsheen Clean Cut compound is a single grade compound with a progressive effect. As it is worked, the abrasive grains break down into finer particles to produce a polished effect.
Apply compound to a firm foam pad and apply it to the surface before starting the machine. Start at a slow speed to avoid excessive splatter and keep firm pressure to work the compound. Gradually reduce pressure and increase speed to polish, but don't go so fast that the surface gets hot.
For final polishing, wipe off any remaining compound, switch to a softer pad and use Pre-wax Shine restorer.
Foam pads are brilliant for compounding or polishing with a sander-polisher. The 200mm size fits directly on to the 180mm velcro backing disc, giving almost a 25% increase in surface area. Select a firm pad for compounding and a soft pad for polishing. Small discs are also available for detail work, especially suitable for restoration on plastic windows.
Big head - high speed
To cover large areas quickly, a machine needs a large head, but the larger the head, the greater the peripheral speed of a rotary disc. Excess speed can cause overheating and permanent damage to fibreglass, so a balance has to be found.
In practice, 180mm (7 inch) is the maximum for a rotary machine. At this size, a good range of slow speeds is essential. Orbitals can go up to a massive 275mm (11 inch) diameter and because of the action, there is no danger of overheating. An 11 inch pad has more than double the surface area of a 7 inch one, so it's much faster to use.
Ideal machines
See our range of sander-polishers here or orbital polishers here
