Cutting back gelcoat.. help please!

[Blutwo]

Hi, I'm new to boating and the YBW forum but a Google search came up with this as a very helpful source of information. So hoping for some advice if can describe clearly enough. Here goes:
I have purchased a boat which has been out of the water for some years and the white gelcoat was dull ( oxidised?)and yellowed. I have treated the boat with an oxalic acid solution and it came up whiter than before and I was satisfied that once cut and polished would look ok. I subsequently lightly 1200 wet sanded to remove areas of grey staining and other deposits. Last night I tried a Farecla G3 Pro D.A cutting compound to get rid of 1200 scratches (not many as it was a brief once over) and some staining that the acid did not sort ( clearly a stronger solution needed). I applied to compound mechanically. What I have found is that far from retaining the ,'whiteness' the compound appears to be 'absorbed' by the gelcoat causing darker/ deeper tint to the whiteness, possibly regressing back to a slightly yellower white if that makes any sense whatsoever. Where I apply the polish to the hull with rotary polishing foam pad, the polish almost stays where it is applied and grabbed / ' absorbed' with little ability to spread to uncoated areas causing these darker areas. These remain when I polish it. The 'darker' polished surface is however shiny, rather than dull finish of the adjacent gelcoat. Clearly as a complete novice I am doing something wrong in the preparation. I am thinking i may have to oxalic this back off and start again, possibly just with a wax polish and not compound..
Would appreciate any advice!

 

[Refueler]

OK ...

I never had luck with the usual ratio mix of Oxalic ... it was ok for light work - but nowhere enough for real stains. I would mix about 300 - 400gr per litre warm water ... plus a handful of wallpaper paste to thicken ..

Apply on wet surface ... leave for a bit and then wash off. Repeat where necessary.

Yellowing of Gelcoat can occur when use of Silicon based Car polishes ... or T-Cut .....

If use T-Cut - you must wash it off completely before applying a non silicon polish.

One trouble with old gel coat ... is after years - it literally becomes porous and does 'stain' from cleaners etc. applied ... also it starts to 'chalk' ... you can see this best on blue gel ... where you see white dust like specs ... marks ,.... and finish dulls. Once it gets to that ... Farecla and similar are only temporary solutions. Many people end up painting the boat. That itself also is only a temp solution ... can end up looking worse.

 

[Concerto]

Welcome to the forum. It would be helpful to know what the boat is and when it was built.

If it is a Westerly, then you will find this document of i cfreated, essential reading. Still worth reading for general information for other brands.
File:Gel coat renovation 19May2020.pdf - Westerly-Wiki

 

[Blutwo]

OK ...

I never had luck with the usual ratio mix of Oxalic ... it was ok for light work - but nowhere enough for real stains. I would mix about 300 - 400gr per litre warm water ... plus a handful of wallpaper paste to thicken ..

Apply on wet surface ... leave for a bit and then wash off. Repeat where necessary.

Yellowing of Gelcoat can occur when use of Silicon based Car polishes ... or T-Cut .....

If use T-Cut - you must wash it off completely before applying a non silicon polish.

One trouble with old gel coat ... is after years - it literally becomes porous and does 'stain' from cleaners etc. applied ... also it starts to 'chalk' ... you can see this best on blue gel ... where you see white dust like specs ... marks ,.... and finish dulls. Once it gets to that ... Farecla and similar are only temporary solutions. Many people end up painting the boat. That itself also is only a temp solution ... can end up looking worse.

Hi, really appreciate your response. I think I may give it another oxalic treatment and then bite the bullet and try just a non silicon polish. Many thanks

 

[Blutwo]

Welcome to the forum. It would be helpful to know what the boat is and when it was built.

If it is a Westerly, then you will find this document of i cfreated, essential reading. Still worth reading for general information for other brands.
File:Gel coat renovation 19May2020.pdf - Westerly-Wiki

Hi really appreciate you providing the document. I've just download and will take a look. The boat is an 1990 Bayliner.
Many thanks.

 

[AngusMcDoon]

It sounds like you have a thick layer of oxidised gelcoat which is porous. 1200 grit really doesn't remove much at all. You may have to have another go. The polishing compound does not get absorbed by the surface once the oxidised layer is gone. With the compound you should be able to get a mirror finish on gelcoat that has been sanded with 1200 grit pretty quickly, even by hand on a small area.

 

[Stemar]

Alternatively, accept that you have an old boat and just go sailing.

One big advantage of this approach for a new sailor is that you'll swear a whole lot less when you put the inevitable scratches on the gelcoat. In a year or two, you'll be bouncing off pontoons less, and you may think it's time to pretty her up.

 

[Blutwo]

Really appreciated. Will probably give the 1200 another go or possible courser as per the PDF I downloaded from previous post. Great stuff.

 

[Blutwo]

Alternatively, accept that you have an old boat and just go sailing.

One big advantage of this approach for a new sailor is that you'll swear a whole lot less when you put the inevitable scratches on the gelcoat. In a year or two, you'll be bouncing off pontoons less, and you may think it's time to pretty her up.

That's great advice as I have been swearing alot! I do just want to get it in the water ( mooring fees ticking also). Very demoralized after I had to cut out the fuel tank and so the whole 'improvement program ' has been scuppered.

 

[eilerts]

The surface of weathered gelcoat is full of micro cracks. Like frosted glass, these makes the gelcoat dull, but also whiter, due to the diffuse reflection of light. The micro cracks also collect dirt. This makes the gelcoat appear darker. When you apply oxalic acid you get rid of the dirt, but not the micro cracks, hence an impressive whitening.
This is not the original tint of the gelcoat. When you go on with the cutting compound and get a nice gloss, it will get darker as you take away the diffuse reflection.
Unless the gelcoat is so heavily micro cracked that you are just filling cracks with compound, I suggest that do another round with cutting compound and try to even it out.

Another fine suggestion is as Stemar writes, just go sailing. I promise you, you will get another chance to get the gelcoat shiny next year, and the year after...

 

[Blutwo]

Hi, thanks for this advice. Really appreciated.

 

[Restoration man]

Have a look at drakes detailing on YouTube , he’s from the states but the process is the same , he goes as low as 500 grit (I’ve never personally gone that course 800 is lowest ive started with on some jobs) this is done with electric random orbit da and sprayed with water , using Mirca Sanding discs available in the uk, Ive often seen people using 1200 even 3000 grit and finer for the first pass but on very chalky gelcote does nothing , ok run over with 1200 as second pass , obviously you need to be careful to not sand through the gelcote but it’s just as easy to go though the gelcote with just the polishing machine leaning on it trying to get shine without wet sanding first , just be careful on external corners as that’s wher you can damage the gelcote the easiest

 

[Blutwo]

Hi, excellent advice. Will certainly take heed. Many thanks.