Cleaning sanding sealing and polishing are the processes involved in restoring an old GRP boat. Having spent the best part of a year doing this I now feel qualified and experienced enough to pass on a few hints and tips.
Firstly, there is no substitute for cleaning and washing. This is one of the most important tasks in the whole process. Dirty boats are covered in sand and grit if you don’t wash this film of dust off, it acts like a very coarse sandpaper and puts scratches and gouges into the gel coat – making the polishing task so much harder.
When the boat is clean you have to wash down with a product that will lift off any silicon which may have impregnated the gel coat through previous use of inappropriate polishes. There are several products that will do this, the cheapest I discovered was Acetone (bought in a DIY store rather than a chandlers).
There is a good deal of confusion about polishing products and processes. The best way I found to describethe process was to think about a friend whose hobby was to find and polish stones. Basically he had a machine comprising a small metal drum turned by a tiny electric motor. The pebble was put in the machine along with a handful of coarse sand and the pebble was tumbled in the sand for days and days. Later the coarse sand was removed and finer grade sand was added in order to remove the scratches that the coarser grade material had made on the pebble. Each few days saw the removal of sand and the addition of finer and finer abrasive material. All the materials were abrasive but each one was less abrasive than the previous. Gradually the pebble ceased to look scratched and actually began to gleam. So it is with gel coat and the trick is to begin with the least abrasive, finest sandpaper you can get away with. The essential message is that although you are ‘sanding’, you are also polishing from day one.
I began to notice the ‘gleam’ in the gel coat when I got down to 1000 grade sandpaper and then the shine improved through 1500, 2000 to 3000 grade.
When you’re happy with the result you need to ‘seal’ the surface. This is where confusion can easily arise because different product manufacturers use a variety of terms – often their ‘sealers’ are described as ‘polishes’ and sometimes their polishes are not sealers. A good sealer contains materials that are absorbed by the Gel Coat, a polish simply sits on top and gleams. The sealer I used is a Starbrite product and I can really recommend it. The active ingredient is PTEF (don’t ask me for more technical information). The recommended process is to rub the sealer onto the Gel Coat and leave it to dry. After about 24 hours you can remove the residue with a soft clean cloth and then repeat the process a second time. On the second cleaning you should notice a deep lustre appearing under your cloth and the Gel Coat begins to feel less like plastic and more like porcelain. I inadvertently began to sand a small part that I had previously sealed and the difference was immediately noticeable. The sealed area was much harder – it felt and sounded different somehow under the sanding paper.
The final stage is to polish with a liquid marine polish and the shine should be outstanding. This final coat is cosmetic and temporary; the weather will degrade it over the season so you have to polish regularly to keep the glassy appearance. Even a dirty boat can take on a temporary glassy gleam if you polish it but for long lasting protection nothing beats a sealer on a clean surface. As I said I use Starbrite’s Premium Boat Polish with PTEF and was very impressed. I have no connection with the company by the way – simply passing on my experience and giving credit where it is due!
USA readers can obtain Starbrite Premium Boat Polish with PTEF hereStar brite Premium Marine Polish Boat Wax with PTEF, 16 oz
UK readers can obtain it hereStarbrite Premium Marine Polish with PTEF14 oz.(paste)