Restoring old gel coat

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magpie2

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Hi I have recently won a project boat on E-bay and it now is sitting on my driveway at home. The boat is constructed of GRP and has been painted but the paint is very thin and peeling off , it does not appear to have been primed or undercoated. Please can someone advise on how to remove the paint and restore the gel coat. Any advice would be much appreciated.
 
gordmac said:
Scrape the paint off or sand it? You get paint stripper suitable for GRP, apparently Nitromors is not a good idea.
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It is paint strippers containing methylene chloride (aka dichloromethane) which should not be used on GRP. However it is now banned from paint strippers other than those supplied for industrial and professional use. Nitromors available from the usual DIY outlets should therefore be OK.
 
VicS said:
It is paint strippers containing methylene chloride (aka dichloromethane) which should not be used on GRP. However it is now banned from paint strippers other than those supplied for industrial and professional use. Nitromors available from the usual DIY outlets should therefore be OK.
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Bugger! Nitromors used to be the one that worked :(

Another useful product bites the dust - just like Hammerite, that used to be brilliant, now it's carp.

Back to the OP. I'd give it a go with the stripper, but depending on the paint, I suspect sanding it off with a random orbital sander may be quicker than Caustic Soda based strippers. Get the discs in bulk from somewhere like ToolStation, or on line. B&Q prices will break you (don't get me started...)
 
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You will probably struggle to get a good finish with the original gel coat. It was probably painted because the gel coat had gone, so once you manage to strip all the paint off you may find you need to paint it again. There is plenty of advice on painting tired GRP on the websites of the paint manufacturers and PBO are currently running a series on doing exactly that job. Whatever you do will be a lot of hard graft, but not much material cost. A good paint finish is not too difficult to achieve and is usually superior to an old gel coat.
 
By far the best way to remove old paint/antifouling/coatings from your GRP hull is by 'soda blasting'. I've tried several painted-on 'strippers' each of which promised much but delivered little - at some cost in money, effort and time wasted.

I was lucky to find a reliable individual with the needed specialist equipment and 'soda' material, which did an excellent job. You're fortunate in the sense that he lives/works in North Devon like you and is also a forumite.

If you're interested, send me your contact info by PM and I'll pass it on....
 
Done this a few times and it relies on having a good 4mm or more gel coat thickness.
I use air wet and dry with 240 grit to get the paint off.
I'd change the disc every square meter or so, so I get through a lot.
It takes a while but anything courser gives you big issues later.
Once back to gel I dry the hull and then draw lines all over with a contrasting waterproof pen.
Then wet and dry this off with 400 grit.
Same process again with 600, 1000 and then 1500.
On a couple of jobs I've used 2000 but this tends to be on only fussy jobs.

By then you should have a nice flatted finish.
Now it's time for the 3m Finesse-it which removes scratches down to 800 and gives a great shiny finish.
Then a couple of coats of wax.

I've reclaimed some old (1970's) hulls and decks using the above.
Actually find it harder with boats built in the 90's to get a great finish than on the older ones.
My guess is the gel on the older ones were hand applied where as the more recent boats the gel was sprayed on.

Overall it takes time and effort but looks great when done.
 
Javelin said:
Done this a few times and it relies on having a good 4mm or more gel coat thickness.
I use air wet and dry with 240 grit to get the paint off.
I'd change the disc every square meter or so, so I get through a lot.
It takes a while but anything courser gives you big issues later.
Once back to gel I dry the hull and then draw lines all over with a contrasting waterproof pen.
Then wet and dry this off with 400 grit.
Same process again with 600, 1000 and then 1500.
On a couple of jobs I've used 2000 but this tends to be on only fussy jobs.

By then you should have a nice flatted finish.
Now it's time for the 3m Finesse-it which removes scratches down to 800 and gives a great shiny finish.
Then a couple of coats of wax.

I've reclaimed some old (1970's) hulls and decks using the above.
Actually find it harder with boats built in the 90's to get a great finish than on the older ones.
My guess is the gel on the older ones were hand applied where as the more recent boats the gel was sprayed on.

Overall it takes time and effort but looks great when done.
Click to expand...

I have little knowledge on renovating old GRP and I find your comments very useful, however, what type of electrical tools did you use for the sanding. I need to sand down my 70's cockpit and deck which has been painted with white paint and it has started to peel off.
 
You can't use wet & Dry with an electrical sander.
On a flatish, horizontal surface I have used my rectangular orbital with wet and dry BUT I do NOT recommend this as it's very dangerous.

That leaves you with air tools orbital or water driven although I've never used the latter but have seen them in action.
Failing that there is always elbow grease and do it manually.
The issue here is that unless you are patient and use a cork or firm foam block it's very easy to take too much off and end up with valleys which are then almost impossible to repair.
Even with the block it's easy to get distracted by a small mark and end up sanding too much away.

If doing it by hand (which is my favoured way for my own projects) step away and take an overall view often - this will hopefully prevent you from focussing on very small imperfections and ending up with a major issue.

I've recently ordered some 1000 and 1500 grit dry 120mm circular orbital sander discs which may be a good solution but I've not tried them yet.
You'll need a mask if doing it dry I expect and masking areas you don't want the dust to go as well.

The trick when using fine grade papers is to change the disc often.
Using the permanent marker technique you will quickly get a feel of how much cut the disc is giving you.
 
magpie2 said:
Hi I have recently won a project boat on E-bay and it now is sitting on my driveway at home. The boat is constructed of GRP and has been painted but the paint is very thin and peeling off , it does not appear to have been primed or undercoated. Please can someone advise on how to remove the paint and restore the gel coat. Any advice would be much appreciated.
Click to expand...

Thanks to all who took the trouble to answer my question. It looks like I have 4 options,
soda blasting,
Paint stripper
sanding and paint
fine sanding and polish.
I will give all some thought as I renovate the cabin and cockpit.
I must say that as a new member to this forum I am most impressed at the response I have received.
 
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