What the hell is blackjack?

[ronsurf]

And why has someone ground off the gelcoat below the waterline and replaced it with this stuff?

It was meant to be a quick haul ashore and repaint the anti foul. . .

 

[penberth3]

And why has someone ground off the gelcoat below the waterline and replaced it with this stuff?

It was meant to be a quick haul ashore and repaint the anti foul. . .

It's a colloquial term for anything black/sticky/greasy/bituminous. I'm guessing you've found that out yourself!

 

[andsarkit]

It's the modern equivalent of gasworks coal tar that used to be put on the bottom of boats.

 

[Iliade]

Was probably epoxy tar: PreviewPreview8:30Painting the Boat - Part 12 - Spraying Coal Tar EpoxyYouTube · SV Seeker5 Oct 2019

 

[ronsurf]

Why would they grind off the gelcoat and put that on?

I'm in the middle of grinding it all off and re-doing the gelcoat. Fun times.

 

[Neeves]

Its also the name of a rather spiffy racing yacht - but I suspect you will not have time for that sort of thread drift

It may have been used to water proof coracles - you are not in Ireland are you?

Good luck.

 

[Stemar]

Why would they grind off the gelcoat and put that on?

It seemed like a good idea at the time? ?

More seriously, could it have been an attempt to treat osmosis?

 

[Quandary]

Epoxy tar was a popular osmosis treatment/protection, as far as I can recall it was effective.

 

[anoccasionalyachtsman]

Epoxy tar was a popular osmosis treatment/protection, as far as I can recall it was effective.

That's my recollection too. @ronsurf - you don't really need gelcoat, just something waterproof and relatively tough to protect the laminate. Gelcoat's just an easy way to achieve it in a mould, and not necessarily the best way, as many have found.

 

[ronsurf]

OK .The trouble is, there are large areas where the blackjack has fallen off, exposing the laminate. It looks like a world map under the boat.

The plan is to grind it all off using a 36 grit paper to provide a key, then a layer of gelcoat, a layer of waxed gelcoat, flat it off with 240 grit paper, prime it, antifoul it, put it back in the water. It doesn't sound too bad if I say it quickly. This was the advice of the guy in the fibreglass supplies shop.

I've got some experience of working with glassfibre from building surfboards - more experience than I have with roofing tar.

 

[PCUK]

Why not paint with several coats of epoxy for an anti-osmosis finish and then fair with epoxy filler?