What's going on with my gelcoat?

rptb1

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Over the winter I've stripped the 30-something-year-old paint from the bottom of my 1983 Newbridge Coromandel, Tammy Norie, mostly in order to prepare her for an osmosis-prevention barrier. A lot of similar aged boats from Newbridge suffer from osmosis and I thought prevention was better than cure.

Under the old paint I find a lot of small circular bumps, a few millimetres across, and mostly below the waterline. Many of them have small cracks around them. If you dig at them they pop out, leaving a crater in the gelcoat only. There is no evidence of moisture or blistering behind them, or any damage to the laminate. They don't seem to fit the pattern of osmosis.

I'll insert a teaser picture here, but take a look at this Flickr album if you want to see more context.

Obviously I'm intersted in doing the right thing (whatever that is) before I add permanent layers of epoxy.

By the way, I'm looking at this today and am happy to scrape and dig (I can lay up glass and gelcoat as needed to fix things) so I can respond to requests and post more pictures.

Thanks!

IMGA0183.jpg
 
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KREW2

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Are they about the size of a 10 coin. If so it looks like blisters have been flat drilled out and filled with Wests epoxy
 

rptb1

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Are they about the size of a 10 coin. If so it looks like blisters have been flat drilled out and filled with Wests epoxy
No. They are about 2-3mm across. There is no pocket of moisture behind them. The material is the same inside as out -- polyester gelcoat. There's no sign of a previous repair. This boat was stored in a garden for 30 years near Inverness. It might be some sort of frost or ice thing.
 

Boathook

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Are they about the size of a 10 coin. If so it looks like blisters have been flat drilled out and filled with Wests epoxy
That's my thought having seen the flickr album ones. I would possibly just refill them (after preparation) with an epoxy resin with a mix of microfibres and filler to give strength and fairly easy sanding.

Edit - just seen OP's bit about them being 2 to 3mm diameter that came in whilst I was typing. Possibly just air bubbles in the gelcoat. Grind out and fill.
 

rptb1

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I've added some more photos (with a ruler for scale!) to the Flickr album.

In particular, this one shows some very old but similar sized features in the deck gelcoat.

IMGA0191.jpg

And here's some possibly related stuff above the waterline, which five years ago the surveyor called "manufacturing defects" and "not harmful".

IMGA0194.jpg
 

rptb1

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Bear in mind I know the complete history of this boat. This is the original gelcoat and there has been no previous osmosis treatment or indeed any kind of repair to the gelcoat or laminate.
 

Ammonite

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Assuming the gelcoat was sprayed I suspect they have been caused by droplets of moisture or oil from a faulty spray gun. See page 155, 5th edition, Fibreglass Boats, Hugo Du Plessis. Tedious to fill but possible and nothing to worry about. Use a high pressure jet wash to pop those that havent done so already, leave to dry and fill with epoxy. I wouldnt bother with gelshield as that will trap moisture in the gelcoat which its bound to have by now and could cause proper bilsters. Once filled, slap on a coat of primocon, antifoul and go sailing.

Edit: sorry missed the comment about being in a field for 30 years so the hull could be dry although if its been in the water for the last few years it may not be given the resins used at the time. Id want to put a meter on it to be sure.
 
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rptb1

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Assuming the gelcoat was sprayed I suspect they have been caused by droplets of moisture or oil from a faulty spray gun. See page 155, 5th edition, Fibreglass Boats, Hugo Du Plessis. Tedious to fill but possible and nothing to worry about. Use a high pressure jet wash to pop those that havent done so already, leave to dry and fill with epoxy. I wouldnt bother with gelshield as that will trap moisture in the gelcoat which its bound to have by now and could cause proper bilsters. Once filled, slap on a coat of primocon, antifoul and go sailing.

Edit: sorry missed the comment about being in a field for 30 years so the hull could be dry although if its been in the water for the last few years it may not be given the resins used at the time. Id want to put a meter on it to be sure.
That seems very plausible given what I've heard about Newbridge, and given what my surveyor said. (He's retired now or I'd bug him about it.) It also makes quite a bit of sense given the way they're distributed around.

There aren't that many bumps with cracks, so it won't be a huge job to fix those up. I'm busy fairing anyway.

The boat has been drying for over a year, and spent last winter in a drying tent. This winter too. My moisture meter shows the hull is dry now. So I'm keen to put a barrier coat on as planned. I may as well make the most of those 30 years! (And nearly every other Coromandel I've come across had bad osmosis.) I'm planning on using West System 422, which is considerably cheaper than Gelshield but trickier to apply.

Many thanks.
 
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BabySharkDooDooDooDooDoo

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rptb1

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Those look similar to the issues I asked on here about regarding SWMBO's Corribee
Yes, those do look similar. Same factory, same resins, possibly the same dodgy spray gun operator! I think the story about freezing opening up the cracks is plausble also, since Tammy stood in a Scots garden under a tarp for many years. You didn't come back to that thread with results. What did you do?
 

BabySharkDooDooDooDooDoo

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Yes, those do look similar. Same factory, same resins, possibly the same dodgy spray gun operator! I think the story about freezing opening up the cracks is plausble also, since Tammy stood in a Scots garden under a tarp for many years. You didn't come back to that thread with results. What did you do?
Sadly we haven't taken it any further as yet, finding the spare time as a two boat household and that one being 3 hours drive away has been difficult.

Recent events haven't helped either!
 

Concerto

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If the bubbles are 2 to 3 mm in diameter I suspect the gel coat was brushed, not sprayed. The bubbles are from poor brushing out of the gel coat mix to work out the air bubble in the mix. My Westerly Fulmar hull has this problem as per the photo. I know my hull was doulbe coated with gel coat, but I suspect the Newbridge Coromandel has only a single coat. The photo of the deck bubbles certainly confirm what I am suggesting. As the hull has been out of the water for 30 years, again I suspect the extremes of hot and cold has caused expansion and contraction of any trapped bubbles causing cracks that allowed moisture to seep in and the freeze causing the area to pop out.

As the main imperfections are below the waterline, all you will need to do is remove all loose areas. Lightly grind the area to clean the surface and fill with either a polyester based gel coat filler like Teroson Gel Coat Filler or epoxy with microbeads. Epoxy is much harder to sand, so I prefer the Teroson filler.

Do not apply the recommended 5 coats of GelShield or similar as recommended by the paint manufacturer. Only apply 3 coats as you may still get some more bubbles appear over the next few years. I am still getting some blistering every time I slip Concerto, 6 years after stripping back to the gel coat and applying GelShield. So do not expect to fix it once and for all. Overtime they will all get filled, so be patient.


P2021058 1000pix.jpg
 

rptb1

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Lightly grind the area to clean the surface and fill ... you may still get some more bubbles appear over the next few years
That's bascially what I thought and what I plan to do. I have epoxy to hand for the barrier coat, and a tub of microbeads that I'm fairing with anyway. Thanks for helping out with your experience.
 

Blueboatman

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Depending on your patience you may choose either to rake out each individual crack with a snapped off hacksaw blade ( this produces a nice square trench for the epoxy to adhere to) or go mad with the grinder and then fill and fair larger areas..
My Corribee experience dates a little earlier than 1983 manufacture.
Despite industry-wide claims that Newbridge quality was, at best, “ highly variable”, I found there was a lot that they got pretty right.

Since you are working on the hull , you may wish to consider adding some grp to the base of the keel(s) to obviate grounding wear.
And wave a magnet across the rudder surfaces to ensure that bronze and not steel (!) rods were used horizontally inside it as rudder shaft ‘ tangs’.
And (!) imho it be worth checking how well the mast heel bracket is secured into the bottom of the boat, you may wish to laminate in an additional plywood collar or socket into which the foot of the mast sits and becomes fully supported all round whilst retaining the standard stainless steel fore-to-aft U bracket and single throughbolt factory set up..
I had a LOT of fun with my old junk rigged Corribee. So much so that having bought it to see what they were like with the junk rig for one short summer trip, I kept it for years and years ( and imported and sold it in the end into the USA)
Oh, and they can get wicking on the gelcoat under the transom/counter because people ( me) tend to overload the hulls and they then sit more deeply immersed.
One preventative ‘ fix’ to that is to simply raise the waterline 50mm or so with epoxy barrier coat whilst you are doing all the other work then apply antifoul or boottop paint over that.
Best luck
 

rptb1

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Despite industry-wide claims that Newbridge quality was, at best, “ highly variable”, I found there was a lot that they got pretty right.
Oh definitely! I'm generally very pleased, even though I keep finding weirdnesses like this one.

Since you are working on the hull , you may wish to consider adding some grp to the base of the keel(s) to obviate grounding wear.
I did that last week, by coincidence. Blog entry linked.

And (!) imho it be worth checking how well the mast heel bracket is secured into the bottom of the boat, you may wish to laminate in an additional plywood collar or socket into which the foot of the mast sits and becomes fully supported all round whilst retaining the standard stainless steel fore-to-aft U bracket and single throughbolt factory set up..
I built a whole new box that also allowed me to adjust my mast rake. Blog entry linked.

I had a LOT of fun with my old junk rigged Corribee. So much so that having bought it to see what they were like with the junk rig for one short summer trip, I kept it for years and years ( and imported and sold it in the end into the USA)
Actually, I'm a bit aware of you. I used an old post of yours called "So heres a thing.......(to any Junkrig corribee entrants)" as a to-do list for improvements. Many thanks for that.

Oh, and they can get wicking on the gelcoat under the transom/counter because people ( me) tend to overload the hulls and they then sit more deeply immersed.
One preventative ‘ fix’ to that is to simply raise the waterline 50mm or so with epoxy barrier coat whilst you are doing all the other work then apply antifoul or boottop paint over that.
Duly noted. Cheers.
 

Blueboatman

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Well you are certainly on top of it all, that is great!

If there is anything specific that I can help with you could always PM me and I will try to help/remember😊
Best wishes for some very relaxed sailing in a thoroughly seakindly boat 👍

I like the idea of adjusting the mast rake-I never got to try that out..
 

rptb1

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Assuming the gelcoat was sprayed I suspect they have been caused by droplets of moisture or oil from a faulty spray gun.
The bubbles are from poor brushing out of the gel coat mix to work out the air bubble in the mix.
I thought you might be interested in this close-up of the rudder gelcoat. These streaks run vertically all over the rudder, and they're not on the surface but buried on the back of the gelcoat, next to the laminate. Brush marks? That would support Concerto's theory.

But the deck and hull have no such marks, and I bet they were sprayed. They also have similar pits and bubbles so that would support Chaktoura's theory. Fortunately there aren't very many on the hull and deck compared to the rudder, so maybe Newbridge's spraying was better than its brushing.

The scratches are from me using an oscillating multi-tool to "pop" the bubbles. It works very well for turning them into craters ready for filling.

IMGA0229.jpg
 

rptb1

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And wave a magnet across the rudder surfaces to ensure that bronze and not steel (!) rods were used horizontally inside it as rudder shaft ‘ tangs’.
No magnetic metals detected. If the tangs are steel, then it's stainless. I know at least one other Coromandel that had rusty steel tangs, so everyone should check their own.

IMGA0230.jpg
 
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