Sadler 25 gelcoat?

[Neil]

I’m currently preparing the bottom prior to coppercoating. In taking off the old antifoul, it seems like there was no coloured gelcoat below the waterline but that this area was subsequently over coated with some coating which then overlapped the coloured gelcoat above the waterline. By the smell of the dust, it was some sort of epoxy: any ideas? While I’ve had to take some of it off to get rid of the last ‘rash’ of antifoul, I don’t want to go over the whole hull to get down to bare fiberglass.

 

[jwilson]

The "overlapped the coloured gelcoat above the waterline" sounds like the boat might already have had the gelcoat removed and replaced with epoxy as an "osmosis treatment". If you take it off you may find that you're not reaching original gelcoat but the hull laminate itself. It's fairly common to have to take "osmosis treatment" up above the waterline slightly., usually then raising the boot-top to cover the join.

 

[Snoopy463]

I’m undertaking the same laborious process as Neil. My Achilles 9m also has unpigmented gelcoat below the waterline. The designer and builder, Chris Butler, believed that no pigment in the gelcoat prevented the onset of osmosis and given the hull is now some 40 years old and has never shown any sign of osmosis, I’m inclined to believe the assertion.
During my antifoul removal, there is evidence of some post manufacture anti osmosis preventitive treatment in the form of a layer of epoxy. This has obviously been removed and will have Gelshield 200 applied before the final Coppercoat.

 

[vyv_cox]

It's many years since I removed the old antifouling from my Sadler 34 and Gelshielded it, but my memory is fairly certain that the gelcoat on underwater areas was unpigmented.

 

[Neil]

So what is the cream coating underneath the blue antifoul and do I have to get rid of all of it?

 

[johnalison]

So what is the cream coating underneath the blue antifoul and do I have to get rid of all of it?

I don't know and I think you will need to get information from someone who has worked on a Sadler 25. Sadlers changed their resins some time in the mid '80s, by which time they were building 26s & 29s, so I assume yours is polyester. Clear gelcoat was often used at the time, so it might or might not be this.

 

[Quandary]

So what is the cream coating underneath the blue antifoul and do I have to get rid of all of it?

Almost certainly two pack epoxy probably applied as an osmosis protection layer, I used Awlgrip which came in two shades of 'cream' so that you could see what you were overcoating, the convention was to apply five layers and if it is properly applied you will do well to remove it. I stripped the antifouling off that boat about 6-7 years later and the Awlgrip coating was too hard to succumb to the scraper.

 

[Neil]

Well, I won't worry too much about the little patches of whatever epoxy coat was put on over the top, it'll still make a good key for the copper coat.

As to the hardness, even the Bahco 665 scraper had problems, but it did take the top layer off in the form of shavings.