Gelcoat cleaning/repair/painting

[rigi36]

Hello

We have a 20ft rowing gig 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.

Tesco bathroom cleaner 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 river so ant-foul is not an issue.

Thanks.

 

[SteveSarabande]

Patio magic gets rid of green

 

[MM5AHO]

Oxalic acid and fairy liquid.
See the thread about Oxalic acid (though they spelled it "Oxalis")

 

[rigi36]

What do we think is in this?

Can I make some myself?

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=271324808372

 

[Rigger Mortice]

Is there a filler/paste we can buy and then sand down?

This stuff is readily available and is easy to use http://www.ebay.co.uk/bhp/gelcoat-filler, but be warned that it is highly unlikely to give a completely invisible repair.......you will be lucky if the colour matches properly. It's better than nothing though.

 

[William_H]

I think the process of boat repair will start with cleaning, as said Oxalic acid is good along with acetone or similar for grease type stains. You may also improve the gel coat with fine wet and dry sand paper. Then fill the scratches with filler as suggesteed. Sand the repairs down again.
You then need to decide if it needs painting. Painting over geel coat is a significant step. It will look better and is repairable on an ongoing basis if you have the same paint. Some paint systems can give a very good finish but it will always be a painted gel coat. So if the result from cleaning and filling is acceptable you should consider leaving it at that. Yes ultimately it will need to be painted but try to put off that day. I used a 2 pack polyurethane paint on my boat. It is hard wearing. Hoever for perfection should be sprayed on. I used a brush and the finish is not perfect. Spraying however requires very good protective gear and an enclosed environment. good luck olewill

 

[rbmatthews]

What do we think is in this?

Can I make some myself?

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=271324808372

It says that it contains acids, so my guess would be that oxalic acid would be amongst those, if not the main one.

You are better off buying oxalic acid crystals off ebay or elsewhere (1 kg: ~£7 incl p&p, e.g. http://www.ebay.co.uk/itm/161053119351), and mixing them into some warm water (140g/litre), and painting it on to the GRP, leaving it for 15 min, then washing it off with a hose. Some folk put in a dash of wallpaper paste to make it stick to vertical surfaces, which works well, but don't let it dry out or it is difficult to get off. Wear protective clothing and goggles as it doesn't do eyes and skin any good.

1 kg of crystals would make about 7 litres, so considerably cheaper than GRP Majic.

Rob.

 

[rigi36]

Thanks

If I make up the solution will it keep or does it need mixing immediately before it is used?

 

[rbmatthews]

I think that it will probably keep for quite a while, but I would just make up enough for what you need each time, as the jar of crystals will take up much less space than the solution.

As a guide, I mix up a litre (=140 g crystals) which is more than enough to do a boat 6m long and about 2.5m wide, which is probably similar to yours.

R.

 

[pcatterall]

If chemical cleaners don't work then ( as advised ) you may need wet and dry to just remove the stained layer of gel coat. try 1000 grit, if that does the trick and you want a really good finish then you will need to remove the fine scratches with 1500 then 2000 grit

 

[MM5AHO]

I find Oxalic acid and setergent far better than wall paper paste.
It doesn't go hard. (paste is glue after all).
It helps get rid of oils and greases and general dirt
The foam of the detergent keeps the acid wet on the gelcoat. (Which is why some use the glue)
It requires some time for the acid to work, nmore at lower temperatures. 10 mins at over 15 deg C, 20 mins at 10C, 30-60 mins at 5C, not worth using under 5C.

 

[rigi36]

Something like washing up liquid?

I'm thinking of:

a) scrubbing with bathroom cleaner to remove most of the dirt/marine growth/green
b) mixing up 1 litre of water with 140g of oxalic acid and some washing up liquid
c) rolling it onto the brown stains left
d) leaving it to dry for a while
e) rinsing it all off

Sound like a plan?
Do I need to be careful with the wood?

 

[Vallich]

A solution of Oxalic works on wood too - rinse off though!