Sealing and Priming: what to believe?

[laika]

I recently fixed some blisters in my rudder by grinding out, leaving to dry, then filling with epoxy and csm. Lots of advice, some differing substantially, kind help from people here, but mostly I followed the advice of the yard boatwrights, only replacing their emulsion bound csm with some powder bound which I bought After sanding the guys here advised me to cover the imperfections with International Interfill 830 (which I've done). Problem is I've got 3 conflictin recommendations for the next step:
Boatwright #1: Coat of Gelshield, coat of underwater primer
Boatwright #2: 3 coats of Gelshield (then AF directly on top)
Chandler: *don't* use gelshield because it's solvent based (despite being 2 part) and whilst fine for use on pristine gelcoat, may get in to imperfections in repaired surface and cause serious problems. Instead use 2 coats of a non-solvent based epoxy like hempel sfe 200 followed by underwater primer

I'm inclined to believe the Chandlery guy who always seems particularly knowledgeable and gives me reasons for things. The boatwrights just say "Use product X because it's what we use" and I wonder if I'm trying their patience with questions but they're too nice to just say "go away". I also wonder if pro products sometimes have the same name as DIY products but a different composition, leading to the conflicting advice.

I don't know what the opaque material the non-filled bits of the rudder are (Would it be gelcoat without white colour?). I *presume* the reason for this first coat(s) is to seal parts which aren't already epoxy. I presume that the primer is because it sticks to AF and expoxy bethan antifoul stick to epoxy. But how to resolve the conflicting advice?

Siimilar confusion exists with what to do with the edges of the iron keel where I've ground away rust and applied rust converter:
Boatwright #1: Interfill 830, gelshield, primer
Boatwright #2: epoxy filler (unspecified), gelshield
Friend: Tar, primer
Chandler: Underwater primer only: The rust will come back forcing the epoxy coat from the keel causing lumps: better just to prime and expect more rust flakes

Of course I expect differences of opinion here, but good reasoning can convince me

 

[jwilson]

Not sure I'd spend money on expensive gelshield on a rudder blade unless it was genuinely moisture meter checked dry throughout. As with hulls, there is a school of thought that says if the main mass of GRP has some moisture in it, sealing it in is bad.

For the rusty bits of the keel, you will probably end up doing it again next year whatever you use, so just primer and AF. Grinding away rust and applying rust convertor is not adequate prep for epoxy - if you want it to stay on.

 

[Pete7]

Chandler: Underwater primer only: The rust will come back forcing the epoxy coat from the keel causing lumps: better just to prime and expect more rust flakes.

I would go with the Chandler on this one. We grind and patch paint the cast iron keels each year were they need doing. Several layers of International Primocon followed by antifoul paint works reasonably well. I stripped one complete side of a bilge keel two years ago and it only needed a couple of touch ups this year. It also dries quick enabling several coats in a day. It is a bit like the Forth Rd bridge but I am slowly winning and each year there is less rust to deal with.

Not sure about the rudder but I thought Gelshield recommended 5 coats? wonder if International Paints are at the boat show, perhaps worth a chat to them. They also have a technical department which I have used before when several coats of Trilux failed in just a few weeks.

 

[alan_d]

It is a bit like the Forth Rd bridge but I am slowly winning and each year there is less rust to deal with.

A Stickler for Accuracy writes: It was the Forth Bridge (i.e. the rail bridge) not the Forth Road Bridge which was erroneously believed to be continuously painted from one end to the other, starting again as soon as they reached the other side. This was never true as the more exposed parts were painted more frequently, but it is true that at one time there was a permanently employed painting crew. The latest paint job on the bridge, completed at the end of 2011, is expected to have a life of between 25 and 40 years.

 

[vyv_cox]

There seems to be some confusion amongst your advisers regarding Gelshield. Gelshield and Gelshield Plus are solvent-free epoxies. Gelshield 200 contains solvent.

Tar - in the past the old Coal Tar Epoxy was excellent stuff but it was banned on the grounds that it contained various aromatics, supposedly a health hazard. The modern substitute is a shadow of its former self and definitely inferior to straight epoxies.

Keel - my iron keel was grit blasted and painted with about five coats of West epoxy, although I suspect that any other make would be as good. There have been a few blisters and small areas of damage, which I have taken back to bright metal with an angle grinder and applied West again. There are holding up well after three or four years.

 

[laika]

There seems to be some confusion amongst your advisers regarding Gelshield. Gelshield and Gelshield Plus are solvent-free epoxies. Gelshield 200 contains solvent.

That would fit. It was Gelshield 200 the chandler was talking about which he seemed to be saying was all that was available to the consumer now that the old non-solvent based Gelshield had been retired. Looking on the International site I see there is Gelshield 200 and Gelshield plus. Force 4 don't seem to stock the latter. Maybe that's what the yard guys use by default and call "Gelshield" (I'll ask them).

This 2 colours to aid layering malarkey is all very well if you don't just need enough to do one side of a rudder, and seems 2x500ml is almost the same as the price for 2.5l.

Keel - my iron keel was grit blasted and painted with about five coats of West epoxy

Forgive my ignorance but is that straight resin? TBH I'm not sure I understand what the difference is between products like Gelshield and regular epoxy. Is it simply that the latter are thinned in such a way as to facilitate application with a roller over a large area and coloured, as opposed to ordinary epoxy which is forumulated for the activities I normally use it for (layering with glass, adding stuff for filling and fairing etc)?

 

[vyv_cox]

West is a clear, two-component epoxy. The two coloured idea for Gelshield 200 is very useful for a hull but I didn't find it too difficult to ensure I had complete coverage of the keel with the clear version.

 

[Caer Urfa]

I recently fixed some blisters in my rudder by grinding out, leaving to dry, then filling with epoxy and csm. Lots of advice, some differing substantially, kind help from people here, but mostly I followed the advice of the yard boatwrights, only replacing their emulsion bound csm with some powder bound which I bought After sanding the guys here advised me to cover the imperfections with International Interfill 830 (which I've done). Problem is I've got 3 conflictin recommendations for the next step:
Boatwright #1: Coat of Gelshield, coat of underwater primer
Boatwright #2: 3 coats of Gelshield (then AF directly on top)
Chandler: *don't* use gelshield because it's solvent based (despite being 2 part) and whilst fine for use on pristine gelcoat, may get in to imperfections in repaired surface and cause serious problems. Instead use 2 coats of a non-solvent based epoxy like hempel sfe 200 followed by underwater primer

I'm inclined to believe the Chandlery guy who always seems particularly knowledgeable and gives me reasons for things. The boatwrights just say "Use product X because it's what we use" and I wonder if I'm trying their patience with questions but they're too nice to just say "go away". I also wonder if pro products sometimes have the same name as DIY products but a different composition, leading to the conflicting advice.

I don't know what the opaque material the non-filled bits of the rudder are (Would it be gelcoat without white colour?). I *presume* the reason for this first coat(s) is to seal parts which aren't already epoxy. I presume that the primer is because it sticks to AF and expoxy bethan antifoul stick to epoxy. But how to resolve the conflicting advice?

Siimilar confusion exists with what to do with the edges of the iron keel where I've ground away rust and applied rust converter:
Boatwright #1: Interfill 830, gelshield, primer
Boatwright #2: epoxy filler (unspecified), gelshield
Friend: Tar, primer
Chandler: Underwater primer only: The rust will come back forcing the epoxy coat from the keel causing lumps: better just to prime and expect more rust flakes

Of course I expect differences of opinion here, but good reasoning can convince me

Hi

When I completly reconditioned my hull when I bought my boat I worked very closly for advice with Richard Jerram Technical Manager of International Paints.

You do NOT put Gelshield 200 or simular onto a steel rudder, after removing all the rust etc and repairs apply 5 coats of Primocon primer then you antifoul ontop as required.

All the above was 7 years ago and worked no problem and I just carry out the normal antifouling when lifting out every two years.

However I have changed to using Jotun Seaqueen instead of Micron Extra due to cost with excellent results with the Jotun Seaqueen, however I always again on advice from Richard use a primer 'before' I apply any antifoul.

Currently 1 x Jotun Vinyguard Silvergrey 88 plus 2 x Jotun Seaqueen and that last 2 years no problem.

Mike

 

[laika]

Thanks: Rudder isn't steel (though keel is iron, which was also a question) but I did mail off a query to International yesterday. Meantime though I've been doing more research. Was going to ask Vyv whether the epoxy he used was the same as the epoxy I use for other things but after reading through the West site I realise that in st's case the answer is Yes, but possibly with a different additive. Now I just have to read and click beyond the wikipedia page on all the different *types* of epoxy.

I didn't realise you needed a degree in chemistry to own a boat. Or do most other people just just slap goop on and not stress out about it?

 

[Pete7]

Or do most other people just just slap goop on and not stress out about it?

Yes

Whilst Vyv didn't much like some of the advice given above, there is a difference in what you originally posted and his answer. Note: you said "I've ground away rust and applied rust converter" whilst Vyv said he had his keel "grit blasted" presumably professionally. Now if you are just patch painting parts of the keel go for the simple option (you're half way there) just add half a dozen coats of Primocon then antifouling. Finally just go sailing, you can't see the goop and it will make not dimes worth of difference on a cruising yacht.

Pete