Hull construction: a layer too far?

[Ducharme]

Okay so I've committed (for better or worse) to liberating myself from the semi-annual ablative painting and am going for a copper epoxy bottom.

To have the copper epoxy adhere properly, my understanding is that I have to remove all paint down to the original gelcoat.

Upon starting in upon this onerous process, this is what I've found:
From the outside moving in there are two layers of what is definitely ablative (dark and darker blue), followed by green, then light blue, and then white.

Here's where things get a little confusing.

The white seems hard like gel coat. Beneath the white is the dark grey (primer?) and then another layer of white gelcoat that appears to be coplanar with the gelcoat above the waterline. Where to stop sanding?

 

[Ducharme]

It almost seems like there is gelcoat followed by a primer or fairing followed by a second layer of gelcoat. Both white layers seem to be of similar hardness.

Is anyone out there more familiar with Beneteau hull manufacturing practices and might further enlighten me? If I can stop (or should stop) at that first, more outboard layer of white gelcoat it's going to save hours of grinding away. And then hours on the couch recovering....

Thanks, all.

 

[Bosman]

While I am unfamiliar with the Beneteau'manufacturing process, my thoughts are :
- you could be seeing anti osmosis barier
- it is not uncommon to use two different colours to ensure proper coverage (this goes for both anti osmosis and anti fouling), ie layers applied in contrasting colours
-sometimes an adhesive improving layer is applied
- i have never heard of two colour gelcoat manufacturing process, but I could be wrong

 

[DougM]

Are you sure that the first layer of white you encontered was gelcoat?
Could it possibly be a barrier coat like Interprotect 2000?
If that is the case, you would probably be OK with stopping there.

 

[Gunni]

What a mess. Someone had previously applied alternating layers of barrier coat in contrasting color (white and gray). You are in the process of compromising the barrier coat and your osmotic protection. The white layer is apparently your top barrier coat, the hull will need a barrier coat reapplied to assure osmotic protection. If you still want to fool with that Copper coat stuff that goes on last, probably hot coated to the barrier.

 

[Davidasailor26]

I'm with Gunni. Most likely gelcoat / gray barrier / white barrier / antifouling. Once you start to sand into the barrier you'll need to build it back up, then apply your antifouling just before the last coat of epoxy is fully dry.