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 describe
the 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 here
Star brite Premium Marine Polish Boat Wax with PTEF, 16 oz
UK readers can obtain it here
Starbrite Premium Marine Polish with PTEF14 oz.(paste)
Seaward
