Gelcoat thickness

mogmog2

mogmog2

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The gelcoat on my Centaur is up to 5mm thick (white layer in pic). Gelcoat available states application rates in microns, typically 4-600 microns, which I think is around half a millimetre. Just wondering what's happened to make such a radical change? Purely cost I'd guess as it's still polyester gelcoat? Thoughts? Thanks.
 

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Westerly used a double layer of gelcoat on most boats, probably it was also brushed on rather than sprayed which made it even thicker. It should never have been anything remotely like 5mm thick though. I can't see what you are describing in your photo.

Whilst thicker gelcoat gives more depth to cut and polish out scratches and scrapes, it increases the chance of stress cracks as it is more brittle than the underlying laminating resin and glass cloth/mat.
 
mogmog2 said:
The gelcoat on my Centaur is up to 5mm thick (white layer in pic). Gelcoat available states application rates in microns, typically 4-600 microns, which I think is around half a millimetre. Just wondering what's happened to make such a radical change? Purely cost I'd guess as it's still polyester gelcoat? Thoughts? Thanks.
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The difference between rollering several layers on by hand and spraying the absolute minimum on to get the boat just beyond the warranty period
 
Haven’t yet found any Gelcoat as thick as 5mm on my Sadler 25 , but certainly found 2-3mm, as geem has noted gelcoat is now sprayed rather than rollered, so is more consistent in thickness, but not as thick as many older boats.
 
Even where the gelcoat is sprayed and very thin you often get corners where it has run and become thicker.
 
geem said:
The difference between rollering several layers on by hand and spraying the absolute minimum on to get the boat just beyond the warranty period
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That is absolute nonsense! Look at 20 year old production boats most of which still have perfect gel coats.

Things have moved on in the last 40 years and there is far more knowledge about materials. The days of porous but brittle when cured gel coats that were slapped on with a floor mop are long gone. It is quote possible to find localised thick areas of gel coat on old boats simply because of the poor application and lack of process control, just as it is possible to find voids and resin starved areas in the layup for exactly the same reason.
 
Tranona said:
That is absolute nonsense! Look at 20 year old production boats most of which still have perfect gel coats.

Things have moved on in the last 40 years and there is far more knowledge about materials. The days of porous but brittle when cured gel coats that were slapped on with a floor mop are long gone. It is quote possible to find localised thick areas of gel coat on old boats simply because of the poor application and lack of process control, just as it is possible to find voids and resin starved areas in the layup for exactly the same reason.
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Can you tell me how gelcoat has changed in that period? There are plenty of 10 year old modern boats here in the Caribbean with zero shine and tatty gelcoats.
We see new boats with cracked gelcoat around chainplates, hatches, winch pads etc so gelcoat certainly hasn't got any more flexible. It's certainly got thinner but it doesn't stop it cracking.
 
Tranona said:
That is absolute nonsense! Look at 20 year old production boats most of which still have perfect gel coats.

Things have moved on in the last 40 years and there is far more knowledge about materials. The days of porous but brittle when cured gel coats that were slapped on with a floor mop are long gone. It is quote possible to find localised thick areas of gel coat on old boats simply because of the poor application and lack of process control, just as it is possible to find voids and resin starved areas in the layup for exactly the same reason.
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I have all of those on my Lloyds build certificated Centaur ?. Generally the gelcoat is a couple of mm thick, but in this area they just filled it with 7mm filler then 5mm gelcoat! It's not structural in that area though, I've had to conclude that it's a styling detail.
 
Westerly certainly applied 2 brushed coats of gel coat and this should be about 2 to 3 mm on most areas. Most other brands that have a single brushed coat of gel coat have about 1 to 1.5mm. Most boats by the turn of the millenium now have 3 coats of sprayed gel coat, but this is only 0.5 to 0.75mm thick. All of this information was told to me by the local glassfibre repair man and from the work I have done on my Fulmar can confirm the Westerly gel coat.

mogmog2, you should have seen my Zoom presentation on gel coat, available to WOA members on the web site, or anyone can see the presentation photos here.
https://wiki.westerly-owners.co.uk/images/8/86/Gel_coat_renovation_19May2020.pdf
 
Concerto said:
Westerly certainly applied 2 brushed coats of gel coat and this should be about 2 to 3 mm on most areas. Most other brands that have a single brushed coat of gel coat have about 1 to 1.5mm. Most boats by the turn of the millenium now have 3 coats of sprayed gel coat, but this is only 0.5 to 0.75mm thick. All of this information was told to me by the local glassfibre repair man and from the work I have done on my Fulmar can confirm the Westerly gel coat.

mogmog2, you should have seen my Zoom presentation on gel coat, available to WOA members on the web site, or anyone can see the presentation photos here.
https://wiki.westerly-owners.co.uk/images/8/86/Gel_coat_renovation_19May2020.pdf
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I heard that on Centaur's they can appear to have a very thick gelcoat. This may not be the case. Apparently after the gelcoat was applied to the mould the first coating of resin had gelcoat mixed in with it. I don't know why they would do this but it does explain the apparent thick gelcoat.
 
geem said:
Can you tell me how gelcoat has changed in that period? There are plenty of 10 year old modern boats here in the Caribbean with zero shine and tatty gelcoats.
We see new boats with cracked gelcoat around chainplates, hatches, winch pads etc so gelcoat certainly hasn't got any more flexible. It's certainly got thinner but it doesn't stop it cracking.
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10 years old is a bit more than just warranty and poor shine and tattiness would occur on a thick gel coat as well if it is not maintained and polished regularly. I am OK with the idea that gel coat in general is a problematic finish in harsh conditions, but not with your suggestion that older boats are better. My Bavaria from 2001 looked like new when it was buffed up for sale in 2015, with the standard colour perfectly matched on the minor repairs despite 10 years in the Eastern Med. Same with cracks - plenty of old boats are riddled with cracks and have been right from the start, but mainly due to poor design rather than thickness of gel coat. Not sure about your claim that it has got thinner on newer boats - do you have any scientific evidence to support this?
 
Tranona said:
10 years old is a bit more than just warranty and poor shine and tattiness would occur on a thick gel coat as well if it is not maintained and polished regularly. I am OK with the idea that gel coat in general is a problematic finish in harsh conditions, but not with your suggestion that older boats are better. My Bavaria from 2001 looked like new when it was buffed up for sale in 2015, with the standard colour perfectly matched on the minor repairs despite 10 years in the Eastern Med. Same with cracks - plenty of old boats are riddled with cracks and have been right from the start, but mainly due to poor design rather than thickness of gel coat. Not sure about your claim that it has got thinner on newer boats - do you have any scientific evidence to support this?
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Read post number 9
Boat design has not eliminated cracks. They are as prevalent in modern boats as very old boats. Good design isn't a privilege of new boats. You only have to look at the Lagoon 450 if you want to see poor design and plenty of cracks
 
Concerto said:
Westerly certainly applied 2 brushed coats of gel coat and this should be about 2 to 3 mm on most areas. Most other brands that have a single brushed coat of gel coat have about 1 to 1.5mm. Most boats by the turn of the millenium now have 3 coats of sprayed gel coat, but this is only 0.5 to 0.75mm thick. All of this information was told to me by the local glassfibre repair man and from the work I have done on my Fulmar can confirm the Westerly gel coat.

mogmog2, you should have seen my Zoom presentation on gel coat, available to WOA members on the web site, or anyone can see the presentation photos here.
https://wiki.westerly-owners.co.uk/images/8/86/Gel_coat_renovation_19May2020.pdf
Click to expand...
Thanks, I'll have a look for it. I'm contemplating a slightly unorthodox idea, that everyone I've mentioned it to doesn't seem to get.
 
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