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Old 14 December 2013, 16:27   #1
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Gelcoat cleaning/repair/painting

Ok so it's not a RIB but I know there's people on here that will be able to help.

We have a 20ft GRP rowing boat that has been sitting in a river for most of the year and so has got a bit of a green bottom.

The boat has now been inverted and so we'd like to clean it and get it looking new again.

http://www.tesco.com/groceries/Produ.../?id=257380034 has been recommended to us. I have tried it with a scouring pad and it seems to work quite well and at 1 for 0.5l it isn't bad. Are the chemicals likely to damage the gelcoat in any way? Does anyone have any other suggestions for cleaning products?

Once clean we'd like to repair a few minor chips/gouges in the hull (example photos attached). Advice for these would be great? Is there a filler/paste we can buy and then sand down?

Lastly, what type of (white) paint should we buy? We don't plan to leave the boat on the water so ant-foul is not an issue.

Thanks.
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Old 14 December 2013, 16:28   #2
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Also had Patio Magic and Oxalic acid suggested for cleaning.
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Old 14 December 2013, 16:50   #3
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What do we think is in this? GRP MAJiC - Gel Boat Hull Cleaner - Removes Stains & Fouling | eBay

Can I make some myself?
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Old 14 December 2013, 17:07   #4
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oxalic acid way to go
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Old 14 December 2013, 17:14   #5
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Do I need to get hull smooth before using the acid? Does it just do the brown stains or will it clear the crap as well?

Should I scrub it with bathroom/patio cleaner first then use acid to get rid of the staining?
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Old 14 December 2013, 17:19   #6
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Fairy power spray is highly recommended on here. The Tesco link doesn't work so not sure if thats what you linked to.

That with a bit of elbow grease should sort the green. Have you jet washed it yet?

GRP MAJiC I'm swure you could get an MSDS if you asked which would tell you the content. I however doubt you'd buy the ingredients any cheaper and things like the gel base may not be listed in the MSDS if they are low hazard.

Chip should be easy enough to fill with either some Gel Coat Filler - eg from Plastic Padding. You wont get a perfect colour match. Or you could use some flow coat*/gel coat possibly padded out with some microballoons. In theory you might be able to colour match that but unless you know the original RAL colour you wont and even then there will be no UV damage to the new gel.

For the chip I'd clean it with soap etc, remove and loose material, rough the area up a bit with 80grit, clean it with acetone, mask about 1inch away, fill hole with some gel padded with balloons, cover with a piece of acetate to help shape, tape it down, let cure, remove acetate & tape, sand back finishing with 1200 wet & dry, then polish up with some t-cut etc.

The gouge... Not sure what I'm looking at. Is it into the CSM? Size?



*use flow coat if you want it to set in air. Use gel if to set sealed from air. Flow also sets sealed.
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Old 14 December 2013, 17:34   #7
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Thanks v useful.

The gouge is not into the CSM and only about 6cm long and about 4mm wide.

If I'm painting the whole boat surely the colour match from the filler won't be too much of an issue?
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Old 14 December 2013, 18:08   #8
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Sorry forgot about the paint. Why are you painting it?? I've never seen a good paint job on gel. That doesn't mean there aren't any - a good one I wouldn't notice...

There are specific paints designed for GRP. You need the matching primer/undercoat too. I suspect some of the bad efforts I've seen have used Dulux!

The gouge then needs cleaning THOROUGHLY as it looks manky! once its clean i'd run a dremmel but down it just to be sure. then fill as described above. Could just flow coat and sand rather than acetate as not trying to shape it.
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Old 14 December 2013, 18:29   #9
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Maybe paint was the wrong term.

Could I flow coat the whole thing
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Old 14 December 2013, 18:36   #10
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Someone may be along to provide advice... ...I've only ever flow coated a smooth surface once in attempt to restore a badly damaged surface.

I wont do it again!

Flow coat is a bit like syrup in consistency. You need a decent thickness to seal the surface but it doesn't smooth like paint does, or at least not in my experience.

It works well inside boats as a floor covering where things are usually meant to be rough...

Now lets wait and see if someone comes along and says different...
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Old 14 December 2013, 18:48   #11
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Judging from your 3rd picture (on right) you have a lot of gel coat damage, stress cracking. Those fine lines and star cracks will just re-appear through any paint that you apply. You might also find that moisture has penetrated into the structure beneath the surface in these areas.
To carry out a proper repair the old gel coat needs to be removed in those areas, any damage to the CSM needs to be rectified or strengthened and Flow coat applied to build up the surface again.
If you are going to paint or flow coat the whole hull I would sand the surface rather than using cleaner. To flow coat you would need to sand down anyway to give a surface for the flow coat to grip to so you might as well get stuck in now and get the 80's grit out! Don't be tempted to use car body filler to repair hull damage, it will just not last.
If you look at my Searider 5.4 project thread you will get the idea of the work that is often required.
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Old 15 December 2013, 01:58   #12
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Whats you plans for the rowing boat after its shiny and white? Gonna take a LOT to convince me that what concrete describes is anywhere close to worth the effort... ...any plans to row it across the atlantic?
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Old 15 December 2013, 11:15   #13
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Hi - we're Sea Scouts so we use the boat quite regularly actually

What you see in the 3rd photo is not star cracks - actually just growths on the surface.

I'll get it clean then take better photos of any chips.

We don't need to paint if it's a lot of effort. Getting it clean is the priority.
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Old 15 December 2013, 11:32   #14
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After reading about fairy power spray i bought some today, excellent stiff, shifted deep salt on my screen, green crap from rear and worked on grp and seats antreat. Well recomended.
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Old 15 December 2013, 13:35   #15
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Will try the fairy power pray and compare it to the cheap tesco bathroom cleaner and let you know results.

Will go for Oxalic acid + washing up liquid solution to clear the remaining stains.
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Old 16 December 2013, 18:03   #16
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Mix the oxalis with wallpaper paste to get a porridge consistency that will stick to the hull. Paint it on and wash off after about 10 minutes with fresh water. Only good for stains though.
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