Renewing GRP hull advice needed

[ryansdesk]

Hi, i am restoring the hull on my GRP sailing dinghy, hopefully to a very acceptable finish. At the moment i am sanding the hull down to get rid of the previous owners paint brush ridges which are evident over the whole hull, i have been sanding this down with a wet and dry paper grade 180 but its taking far to long and my arms abvout to drop off, i was thinking of using a more course paper, say about 120, to get rid of the ridges and then go over it with the 180 paper before giving it a first coat. I wondering if this is a good idea?

My other question is to do with the actual paint, my origianl plan is to use international prekote below the finish coat of toplac however looking at the back of the prekote tub i may be better haveing an initial layer of primer over my newly sanded hull instead of just prekote. Bearing in mind that it is a GRP hull which will have some of whatever coated the hull in the first place still left on it in parts, whats the advice here,
Primer, prekote, toplac or just prekote and toplac?

 

[oldharry]

Why not use an electric sander like the rest of us?

120 grade wet or dry used wet will cut the surface back well enough, you should then go over again with something like 300 grade, then if you want a really good finish, finish off with 600 - 800 grade used wet.

Car finishers will go as high as 1200 or even 1500 grade in the final polishing pre painting stages, but this is only worth it if you are planning to spray paint.

Assuming you are going to brush the paint on, then you will need to do it all over again between each coat, and you will have the greatest difficulty in eliminating brush marks entirely.

So your arms will have fallen off by the time you finish! But preparation, preparation and more preparation is the only way of getting a really good paint finish. Sometimes (most of the time!) it feels as though you are putting paint on, then sanding it off again.

 

[Seal_surfer]

May already be doing this, but renew the W&D paperevery metre or less ofsanding, when you can feel its no longer cutting through. I always dab the paper along a piece of old soap bar after every time you rinse in water bucket (after every sq foot or so). always sponge/rinse off at these times to remove paint slurry build up from hull. This will get the best effect for effort put in. Something like 180 grit should be quite coarse enough unless you have a real porridge of old paint to get through.
Be wary of power sanders unless you are competent as it could easily cut too far on tighter curves of a hull - even going through gelcoat.
I can highly recommend 2 pack polyeurothane on something this size, if you can remove all old paint. Did Wayfarer, Ucoat + 2 coats, 10 yrs ago - still looks great. Search forum for tips, but get everything well laid out so no delays during applying paint (premixed a few modest batches and held back in freezer until req'd during the session)

 

[ryansdesk]

wasnt too sure about the wet sandpaper and electric sander, not a good combination, the dry paper just clogs up to fast so thats why opted for the dead arm scenario. But the 120 paper sounds good might even risk 100 then followed by the 180. At back of international tub says the 180 is sufficient since it fills scratches this size. Or is that wishful thinking but have to say of the bits ive completely with the 180 i cant feel any scratches with my fingers it feels super smooth.

 

[Mudplugger]

If you are using Top-lac, and worried about brush marks and don't have the facility to spray. Have a look at the Jenny brush range (squares of foam on astick) inexpensive and very effective! IMHO