Bringing back the shine on GRP

BogMonster · 20 March 2011, 11:12

I did a nasty to the bow on Seawolf the other day - I recover onto a shallow sandy beach and normally head in with power on then at the last minute trim the engine out of the water and coast onto the sand - unfortunately there is a nasty sharp obstruction buried in the sand off to one side and a gust of wind spun the boat around just as I lifted the engine out, too late to do anything and crunch... gashed right into the weave of the fibreglass on the V of the bow. There was some swearing. Quite a lot in fact.

Anyway I have some white Plastic Padding gelcoat repair and after drying it out I have ground the damage back, patched it and sanded it down so it looks OK (glad I got white - easiest colour to patch up

) but the repair instructions on the gelcoat kit say to wax it afterwards to bring back the shine. I wet and dried it with fine paper and waxed and polished it but it still looks quite dull - am I doing something wrong here? I'd sort of assumed you could get a gelcoat repair to look almost invisible but this is far from it if you look closely - what's the secret? Do I need to get a powered buffer or something and just give it loads of stick with that? Should you use cutting polish (T cut) or not? (Didn't want to take the shine off everything else...)

It doesn't show too badly being white (looks better than the green repair kit did on my orange Humber hull

) but being a new boat I'd just like to get it as good as possible. I know there were some cosmetic glitches on the console when that was moulded and you can't even see where they were now - ok so that was done by a professional but it must be possible to make a repair near enough perfect but I just don't know how to get the final finish right.

Any tips would be welcome, ta

Ian M · 20 March 2011, 11:53

What grade of wet and dry are you using?
Not sure about the gelcoat repair stuff, but true gelcoat needs almost polishing, working down through the grades of wet and dry to, well 1500 is what I finish with. Then a good buff up with 3M Perfect-It Fast Cut Compound usually does the trick.

martini · 20 March 2011, 12:33

You might need to leave it for a few days/weeks to cure properly, the harder it goes the better the finish that's possible. I've got some here and read the destructions, doesn't say anything about long term curing but you never know

ps I buggered my metz, turns out if you screw the longer SO239 into it too far it pushes through the bottom of the antenna

still works though

willk · 20 March 2011, 13:29

Bummer on the damage!

Let the gelcoat filler harden for a few days. Sand it back, finishing the final surface with 1200 grit wet/dry. Clean and give it a quick rub of compounding paste followed by one with polishing paste. I used 3M machine polish on a small job recently and the finish was very good. Top it all off with a good waxing.

BogMonster · 21 March 2011, 00:35

Thanks, I think it was probably only about 800-1000 paper, it was the finest I could get but it wasn't 1500 anyway.

Hadn't thought of the hardening process, I did it the following day after it had hardened, but haven't tried again.

I have a Draper dremel multi-tool which I think has polishing discs with it, would that be a good thing for buffing up?

I won't find that 3M stuff locally - what about automotive T-Cut would that be OK?

I might have another crack at it to make the repair a bit neater (and there's a couple of smaller gouges that also need dealing with) before I really go to town with the polisher.

Thanks all

willk · 21 March 2011, 00:50

I dunno about T-cut - maybe for the final polish before waxing? You must have compounding and polishing stuff for cars out there - it's the same crud.

Try White T-Cut if you can't get anything else

You may need something a touch more "buff" than the Dremel, unless you want to sign your work when you're done...

:-P

dougal_22 · 22 March 2011, 19:24

a quick tip dont go to mad with the wet and dry.. get hold of some farecla g3 or there marine grade cutting compound it cuts back even the most heavily oxidised gell coat. a quick going over with 3000 grit minimum if u start to get any ware with cutting compound and then use wet and dry again u are just wasting time, sorry if im telling you how to do it just things i learnt in the body shop.

spartacus · 22 March 2011, 19:50

Quote:

Originally Posted by willk

I dunno about T-cut - maybe for the final polish before waxing? You must have compounding and polishing stuff for cars out there - it's the same crud.

Try White T-Cut if you can't get anything else

You may need something a touch more "buff" than the Dremel, unless you want to sign your work when you're done...

:-P

Give the T-Cut a miss, you may end up staining the gel-coat. As suggested Farecla G3/G10 compounds give excellent results used with a variable speed rotary mop. If there's any petrol-heads on the island driving shiny Land Rovers, then they may have Menzerna polish, which will give optimum results.

dougal_22 · 22 March 2011, 20:26

i agree about avoiding t cut, not heard of this one landy lovers may use so cannot comment,, i would also recomend using a propper mop and pollisher, not a halfords job for this type of work...

jwalker · 23 March 2011, 13:18

Nah, T-cut'll be fine for the final polishing. Forget the Dremel and use elbow grease.

Before the firing squad arrives, I'm not suggesting the other buffing systems don't work.

Since you've got limited materials available, going down to around 1000-1200 grit wet or dry then automotive cutting paste then T-cut will likely be fine. Just one thought though, if your gelcoat filler stuff contains a filler powder as car body fillers do, you're unlikely to get as crisp a shine as you would from neat gelcoat. A good finishing wax is Simonize Original but it's getting a bit like hen's teeth, I'm saying this cos it used to be a common product some years ago and you might just have some kicking around on a garage shelf.

Good luck and change your beaching technique, I doubt the sand is finer than about 120 grit.

BogMonster · 24 March 2011, 09:16

Ta all.

The fancy compounds are simply not available here so it's T cut or nowt. Actually now it has been "buffed" by the South Atlantic a couple of times it doesn't look too bad unless you get close up.

JW, it wasn't the 120 grit sand that was the problem, it was the 0.00001 grit lump of rusty steel sticking out of the beach