testing if primer is 2 pack or one pack

[Rhylsailer99]

I have almost finished scraping antifoul , some areas i have took back to the silver grey primer . i made a small batch of west epoxy and painted over the top of the primer . there was no reaction would it be a safe bet to pain over with jotun 87 winter grade ?

 

[dankilb]

Jotamastic 87 will be happiest going on to abraded GRP/gelcoat, second best would be abraded epoxy coating, but if it turns out the silvergrey primer is something like old primocon (vinyl primer) it’ll be least happy on that.

Are you trying to build up a barrier coat? In which case the substrate is important (paint free, dry, properly abraded).

If you’re just using it as a primer coat before antifoul, it’s less important what’s underneath.

I don’t know whether the lack of reaction guarantees it is epoxy, but someone cleverer may come along and confirm.

 

[Rhylsailer99]

Jotamastic 87 will be happiest going on to abraded GRP/gelcoat, second best would be abraded epoxy coating, but if it turns out the silvergrey primer is something like old primocon (vinyl primer) it’ll be least happy on that.

Are you trying to build up a barrier coat? In which case the substrate is important (paint free, dry, properly abraded).

If you’re just using it as a primer coat before antifoul, it’s less important what’s underneath.

I don’t know whether the lack of reaction guarantees it is epoxy, but someone cleverer may come along and confirm.

Was just thinking of a barrier coat of a 2 pack primer to protect the gelcoat then use a single pack primer then antifouling.

 

[Rhylsailer99]

I just purchased 750ml of gelshield ill try that and see what happens, I can use it on my rudder and skeg which is 100% down to gelcoat now.

 

[dankilb]

Like lots of these things, it comes down to a balance between what you ideally should do and how much time/effort you can actually be ar**ed with.

As a recently learned from my own thread on Jotun coatings - also worth knowing they are solvent epoxy (whereas West and other laminating resin are solvent free). Jotun also stinks! So lots of indications it would be harsh on any 1 pack coating it’s applied over.

So I would test an area with the Jotun first to see how that reacts.

Have you got Jotun No. 17 thinners? If not, worth having anyway. A wipe with that could also help test for reaction. And it’s good stuff to clean the surface prior to paint anyway.

Of course, the ‘right’ way for what you want to do would be to keep sanding down to gelcoat. But it’s a question of that vs. when you want to get back in the water or move on to the next job.

 

[Rhylsailer99]

Like lots of these things, it comes down to a balance between what you ideally should do and how much time/effort you can actually be ar**ed with.

As a recently learned from my own thread on Jotun coatings - also worth knowing they are solvent epoxy (whereas West and other laminating resin are solvent free). Jotun also stinks! So lots of indications it would be harsh on any 1 pack coating it’s applied over.

So I would test an area with the Jotun first to see how that reacts.

Have you got Jotun No. 17 thinners? If not, worth having anyway. A wipe with that could also help test for reaction. And it’s good stuff to clean the surface prior to paint anyway.

Of course, the ‘right’ way for what you want to do would be to keep sanding down to gelcoat. But it’s a question of that vs. when you want to get back in the water or move on to the next job.

Yes I am in 2 minds as it's took me ages to get to the stage of removing all the antifoul one half of me is saying just paint a few coats of one pack not in primer over then antifoul and move on

 

[dankilb]

I just purchased 750ml of gelshield ill try that and see what happens, I can use it on my rudder and skeg which is 100% down to gelcoat now.

Gel shield plus is also solvent-free, unlike Jotun. There’s no guarantee how they’d react. Be sure to wait the full cure time and abrade/key the surface if you end up combining the two anywhere.

 

[dankilb]

Yes I am in 2 minds as it's took me ages to get to the stage of removing all the antifoul one half of me is saying just paint a few coats of one pack not in primer over then antifoul and move on

Yeah good point, there. Reckon a fair number on here would vote just do some good coats of vinyl primer (Primocon or Vinyguard) and a/f and you’re good to go.

Is there any particular reason to want a barrier coat? Was there any osmosis? The rudder I understand, because of the repairs. But if the rest of the hull is sound, you could just do any repaired areas and leave at that.

You’d also want to be confident the hull is really dry for 2-pack coating. That means moisture meter readings comparing areas below the waterline with the topsides. Otherwise it might blister and fail, leaving you with a problem where you had none before (assuming the hull is fair now?).

 

[Rhylsailer99]

cheers i will just use vinyguard as i have 5 litres of that , there is no osmosis on the boat just a few deep scratches on the bilge keels. i think it helped that it was on dry for about 7 years and when it is in the water it dries out twice a day at low water, maybe that helps against osmosis just guessing.

 

[James W]

I’ve just had to make good a hull where somebody epoxied over wet glass and, trust me, you do not want to have that problem!

 

[dankilb]

Yup, as @James W says, epoxy coating is not a 'win/win' - in that, if something isn't quite right with the substrate (high moisture, incompatible old coating, not properly prepped) it can cause worse problems. As you know, it cures rock very hard too, so if something does go wrong it's a nightmare to remove!

As it sounds like the hull itself is fine, I think you're right that Vinyguard is the way to go for a primer.

Jotamastic is great stuff. It has an additive that makes it extra resistant to moisture ingress. It would be a good 'barrier' coating for your repairs/keels/rudder. You can barrier coat with several layers of West instead, but we know it costs more, more sensitive to temperature, etc. Three or more coats of Jotamastic is a good alterative. More than three coast (at 300 microns each) is over a millimetre thick, water resistant, tough, etc. And you can just slap it on like paint, following the Application Guide. ?