Gelcoat restoration. Advice, please.

[Tiger Moth]

I've just bought a Caravela 22 which probably hasn't been in the water for about 20 years. It's in good order considering but the gelcoat has dark staining, whether from an old cover or staining from rainwater I don't know.
Cream kitchen cleaner has taken the initial dullness off but not the staining. T-Cut bounced off and the expensive jollup that you paint on and wash off also failed miserably. Has anyone had the same problem and met with any success? If so, please tell me how. I'd really prefer not to have to paint as I've always hated seeing the dimpled finish of a roller painted hull.

 

[Concerto]

Have a look at my presentation on gel coat renovation. Initially I would try using a cutting compound, and if that does not work you will need to remove the top surface with a fine wet and dry paper used wet and then compound to a shine.

https://wiki.westerly-owners.co.uk/images/8/86/Gel_coat_renovation_19May2020.pdf

 

[AngusMcDoon]

1200 grit sandpaper used wet with a cork backing block to reduce scratches and get rid of stains where necessary, Silverline variable speed polisher with a lambswool mop run at the lower end of its speed range, Farecla cutting compound, a weekend of aching arms, & it will be so shiny you'll be able to see a reflection of your fizzog in it. Have a good collection of clean cotton rags to remove the remains of the compound.

If you run the polisher too fast or press too hard you can scorch the surface of the gelcoat making it go brown, and then you'll have to sand it out. You'll probably do this a few times at the start but it's not a disaster. It sands out easily.

The thing to remember is that it's an old boat so don't aim for perfection. It's better to make all of it significantly better than it is now rather than spending too long trying to get perfection and then never completing it. The transformation for a weekend's work can be remarkable.

 

[William_H]

I am not familiar wityhb the products mentioned however. Before you start grinding away the surface try out chemical cleaners. Start with oxalic acid. The try acetone or similar solvent. Then try bleach. If all fail then as said cutting compound or fine wet and dry sand paper. ol'will

 

[AngusMcDoon]

I am not familiar wityhb the products mentioned however. Before you start grinding away the surface try out chemical cleaners. Start with oxalic acid. The try acetone or similar solvent. Then try bleach. If all fail then as said cutting compound or fine wet and dry sand paper. ol'will

The level of staining & scratches in the photo suggests to me it's beyond that. The op says he's already tried various chemicals to little effect. The surface of the gelcoat will have gone porous over the decades & absorbed contaminants beyond the reach of chemicals. The only solution is likely to be to remove that porous surface mechanically.

 

[RunAgroundHard]

… The surface of the gelcoat will have gone porous over the decades ..

Is that a thing? I have never heard of that before. Not doubting, just curious.

 

[Chiara’s slave]

Must admit, I would never put acetone anywhere near my gelcoat. Oxalic acid is always worth a go as it’s cheap and effective, particularly on rust marks. But I think the OP is going to find that Angus is right.

 

[Neeves]

So... the gel coat has gone porous and the pores have allowed 'contaminants' to enter the pores and cause the discolouration. If this is the case then chemicals, bleach, oxalic acid (and both - maybe separately or together) should similarly be able to enter the pores and possibly do their work.

The problem is providing the environment allowing the chemicals the opportunity to be absorbed.

Wall paper paste and bleach and then wall paper paste and oxalic acid come to mind but expecting a miracle in a day, or week with 20 year old staining is, maybe, optimistic - but must be worth a try. Other options based on the same idea (and the idea maybe flawed) must be worth a try.

If it works, fingers crossed, then the pores need to be filled - wax is an idea.

The key, if its the porosity, is getting the chemicals into the pores.

The yacht is small - a boat bag comes to mind - fill with bleach, leave for ...?? a long time, fill with oxalic acid ...leave for (would either be allowed??) is this too expensive??

Jonathan

 

[RunAgroundHard]

Neeves, they are not sensible solutions in my opinion, nor even close to worth a try. It’s a small boat, a weekends worth of work compounding and polishing is all it takes, a well proven solution for aged gel coat.

Maybe you were being ironic.

 

[Stemar]

A tub of oxalic acid and a bit of wallpaper paste is cheap enough to be worth a try, IMO.

Maybe I'm getting old and lazy, but polishing even a small boat by hand is hard work and, even with a polisher, it's equally hard, just quicker. Also, unless you've already got access to one, polishers aren't especially cheap.

 

[Canopy Locked]

Wet and dry sanding is the only way to sort this. I have just done my small 17ft boat over the winter. It had a myriad of deep scratches and faded areas. Started out with 1200 grit, but that did not touch it. Ended up going down to 800 and then working my way back up to 1500 before starting on the polishing compounds. Looks great now - One thing to remember... If it's an old boat (mine is 16 yrs old) it will generally have a much thicker layup of gelcoat than a brand new boat today. Don't be afraid to take off the top layer.

 

[AngusMcDoon]

So... the gel coat has gone porous and the pores have allowed 'contaminants' to enter the pores and cause the discolouration. If this is the case then chemicals, bleach, oxalic acid (and both - maybe separately or together) should similarly be able to enter the pores and possibly do their work.

The problem is providing the environment allowing the chemicals the opportunity to be absorbed.

Wall paper paste and bleach and then wall paper paste and oxalic acid come to mind but expecting a miracle in a day, or week with 20 year old staining is, maybe, optimistic - but must be worth a try. Other options based on the same idea (and the idea maybe flawed) must be worth a try.

If it works, fingers crossed, then the pores need to be filled - wax is an idea.

The key, if its the porosity, is getting the chemicals into the pores.

The yacht is small - a boat bag comes to mind - fill with bleach, leave for ...?? a long time, fill with oxalic acid ...leave for (would either be allowed??) is this too expensive??

Jonathan

Great in theory, if only dirt were so accommodating! We all have experience of dirt getting into other absorbent materials and never being able to get them out again. Rust stains on sails is a good example; you can reduce them but never eliminate them completely. A chemical resolution probably won't work in practice for the op, because even if the chemicals remove or disguise the contamination the dusty porous surface will reabsorb them again quickly. This damaged surface needs to come off for a decent long term fix. Filling the damaged surface with wax doesn't work for long.

 

[Neeves]

Neeves, they are not sensible solutions in my opinion, nor even close to worth a try. It’s a small boat, a weekends worth of work compounding and polishing is all it takes, a well proven solution for aged gel coat.

Maybe you were being ironic.

No, I'm with Stamar. Oxalic acid and bleach are cheap - if you can get them to stick, wall paper paste (any other ideas) small poly sheet adhered to hull (with paste cocktail inside) - its better than sanding.

Jonathan

 

[AngusMcDoon]

Is that a thing? I have never heard of that before. Not doubting, just curious.

Yes. If you have an old UV damaged gelcoat surface where fine dust comes off when you rub your fingers over it the surface is now porous. A test is to draw a line on it with a marker pen & then try to clean it off. On a porous surface the mark will remain. On a new or recently compounded non-porous surface the mark will come off. The porosity is only very thin. You can remove it every 20 years with no risk of running out of gelcoat in a lifetime. Compounding will usually get rid of it but fine sanding will be needed on scratches or bad staining. The picture in #1 has both.

 

[AngusMcDoon]

No, I'm with Stamar. Oxalic acid and bleach are cheap - if you can get them to stick, wall paper paste (any other ideas) small poly sheet adhered to hull (with paste cocktail inside) - its better than sanding.

Sodium hypochlorite in bleach attacks polyester gelcoat and if used should be washed off quickly. It must never be left to linger. Unfortunately with a probably 40 year old porous stained gelcoat surface fine sanding & compounding is the only solution that will work.

 

[AngusMcDoon]

Also, unless you've already got access to one, polishers aren't especially cheap.

Silverline 1200 Watt variable speed polisher can be got for about £55 to £60. Silverline is good enough for non-professional occasional use. A proper powerful rotating polisher is needed for this job. The cheapo car accessories shop vibrating ones aren't up to the task.

A good way to reduce aching arms when polishing the hull sides is to support the weight of the polisher from a halyard or stanchion with some bungee attached to allow movement.

 

[johnalison]

Wet and dry sanding is the only way to sort this. I have just done my small 17ft boat over the winter. It had a myriad of deep scratches and faded areas. Started out with 1200 grit, but that did not touch it. Ended up going down to 800 and then working my way back up to 1500 before starting on the polishing compounds. Looks great now - One thing to remember... If it's an old boat (mine is 16 yrs old) it will generally have a much thicker layup of gelcoat than a brand new boat today. Don't be afraid to take off the top layer.

I agree. I had to sand a small patch after an abrasion and it soon came up like new.
You can be as rough as you like. In the last resort you can end up painting the hull, which will be necessary sooner or later anyway.

 

[AngusMcDoon]

Must admit, I would never put acetone anywhere near my gelcoat. Oxalic acid is always worth a go as it’s cheap and effective, particularly on rust marks. But I think the OP is going to find that Angus is right.

IPA is less aggressive to gelcoat than acetone & will remove greasy marks effectively. Oxalic acid seems to work wonderfully in front of your eyes on brown waterline stains, but 2 weeks after launch they are back, because the porous surface has absorbed the contamination again.

 

[AngusMcDoon]

I agree. I had to sand a small patch after an abrasion and it soon came up like new.
You can be as rough as you like. In the last resort you can end up painting the hull, which will be necessary sooner or later anyway.

For someone doing this the first time 1200 grit is a good starting point for sanding as it's almost impossible to go through the gelcoat with this grade. It's enough for most stains. For scratches that do not penetrate the gelcoat but have depth that you can feel with your thumbnail it will be necessary to start with 800 or 400 grit, but care must be taken.

The technique is not to sand with 400 until the scratch is completely gone but use the coarse grit until it's almost gone, then go to 800 sanding until you can still see it but not feel it, then 1200, then compounding.

 

[Chiara’s slave]

IPA is less aggressive to gelcoat than acetone & will remove greasy marks effectively. Oxalic acid seems to work wonderfully in front of your eyes on brown waterline stains, but 2 weeks after launch they are back, because the porous surface has absorbed the contamination again.

You have to follow up oxalic acid with wax. But I’m sure you’re right on bad staining, only compounding removes it for good. Followed by wax or it will be back, if not in a fortnight, then in a few months.