G4 problem?

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jonh
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G4 problem?

Post by jonh » Tue Feb 24, 2015 7:55 pm

Hi all! This is my first post on the forum , although I did plunder it when renovating N12, 3215 last year.Having stripped the decks,I let them dry out for a couple of weeks then used G4.I was delighted to get on four coats in a day and ,after curing ,the finish was most impressive.I wet and dried it and then finished with three coats of classic varnish.All good so far,but the boat has been outside all winter and I have now got the' speckling 'effect under the coating which usually indicates the dreaded presence of water/damp.Someone who looked at it suggested that moisture might have come through from the underside of the side decks which I regret I did not treat in any way.Help! Will I need to get the G4 off,and how do I do it?Any suggestions would be most welcome.

Rupert
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Re: G4 problem?

Post by Rupert » Tue Feb 24, 2015 9:18 pm

It could be damp coming through, I guess.

To remove it, a hot air gun has done the job for me in the past. Can't remember how much of a pain it was compared to normal varnish, though.
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Re: G4 problem?

Post by Obscured by clouds » Tue Feb 24, 2015 11:25 pm

I had similar speckling on the Unit, but i put that down to putting on the last coat whilst the G4 was 'going off'.

G4 is primarily sold and presumably formulated as a pond waterproofer, being painted directly onto concrete to form a waterproof barrier. so we have moisture above, but the concrete will also be be damp. would that not have the same effect? I guess it does'nt matter in a pond, or if the G4 on a deck is painted, but I can see the problem if varnish is involved.

Perhaps we need to go back to CPES.
Tony



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Stephen Hawkins
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Re: G4 problem?

Post by Stephen Hawkins » Wed Feb 25, 2015 10:57 am

I understand that one of the advantages of G4 was that it comes off just like Traditional varnish, i.e. with a heat gun, rather that dynamite (for epoxy and hard 2pack finished). Having said that, I have not yet had to remove large sections of it.....yet.

I used it on my N12 (Sparkle) this winter when I re-decked it. I also put about 3 coats of Hempel Favourite trad varnish over the top of it in some pretty cold conditions.

I also used it on the deck of my old Merlin Rocket. But I have since sold that on. I am not sure what work the previous owner did on that boat since, other than he made it look fantastic.

Spider, one of my other N12s had G4 put over a thinned coat of varnish on the deck, during the summer, and it has spent all winter outside. I have not seen any issue with that. But will be looking closely at it when I am next at the sailing club.

Water coming from underneath, is an interesting theory, but it would have to get through 3 or 4 layers of wood/glue to do that and it would have to be very wet?

Why not try and rub down through the varnish layers on a specimen area and see if the issue lies between the G4/varnish interface. I suspect that if the boat has been in damp/cold conditions all winter it might actually be the varnish that has failed on top of the G4. I would be interested to hear what your findings are.

Cheers

Steve Hawkins
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Ed
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Re: G4 problem?

Post by Ed » Wed Feb 25, 2015 2:44 pm

Photos would (or may) help.

What kind of speckles? Or bubbles?

If bubbles, knock the top off one and see if it has water in it?

If you scrape it, how does it come off. Does the varnish come away from the G4 or do they come off together.

I have heard of the theory that water has come through a deck and attacked the coating adhesion on the other side....and maybe this happens, but no proof for it at all. I think it could happen with old knackered ply. And of course with varnish, which is pretty porous the damp can go straight through the varnish and attack the adhesion layer directly.

Without further info, I could only guess /suggest that the most likely culprit as Stephen says is the G4 to Varnish join.

This is notoriously difficult to get right. I love G4 with this one 'fly in the ointment'....It is really hard to get a decent and firm join between the G4 and subsequent layers. It will bond to itself easy enough if hot-coated and not allowed to harden. But once this happens, you really need to leave it for a few days (weeks) and then wash/sand/wash and maybe sand/wash again to get it totally clean of any solvent and give a mechanical key for subsequent coats.

Problem is that when you get this wrong, you can't tell until either the porous varnish lets some moisture through which then frees the varnish from the G4 or you get a bump, and the shock literally knocks off the varnish, but leaves the G4 attached to the wood.

What is good about this though is that it is often possible to remove and replace the topcoat varnish without damaging the G4 or the wood it is protecting.

But as I said, try getting a scalpel into a bubble, or under the varnish and see how easy it peels off.

Good luck, tell us how it goes and as ever......send photos.

eib
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Re: G4 problem?

Post by JimC » Wed Feb 25, 2015 3:32 pm

Ed wrote:I have heard of the theory that water has come through a deck and attacked the coating adhesion on the other side....and maybe this happens, but no proof for it at all.
Happened to me with when I stupidly left a boat left upside down all winter with inadequate covering and water pooled on the underside of the side decks. It was really clear because where there was tank under side deck (so no pooling) the varnish was fine, and where there was no tank and water had pooled the varnish had lifted.

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Re: G4 problem?

Post by Stephen Hawkins » Wed Feb 25, 2015 4:15 pm

I have a flat topped cover that was good at holding the water close to the varnish side decks. It lifted the varnish right off over last winter, wherever the wet cover touched the varnish. No G4 in this instance, but lots of layers of varnish ruined either way particularly near the rear quarters.

This was another reason why I chose to sort out Sparkle this winter.

Cheers

Steve H
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Rupert
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Re: G4 problem?

Post by Rupert » Wed Feb 25, 2015 6:59 pm

Me too, Steve - a black plastic one on the Minisail. I replaced it with a breathable one that cost more than the boat, and problem solved.
Rupert

jonh
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Re: G4 problem?

Post by jonh » Wed Feb 25, 2015 7:15 pm

Thanks for the replies with some very good suggestions.I will definitely scrape a small area to check whether the damp could be between the G4 and covering varnish layer when down at the sailing club next weekend.Supporting JimC's observation,I only have water damage on the side decks, whereas the foredeck and rear buoyancy tank are fine.This seems to suggest that the damp might have spread up from beneath the side deck, if indeed it proves to be under the G4.Incidentally, I have now rigged something beneath the cover so that it does not lie flat on the decks at all. We live and learn,I guess!
Cheers
JonH.

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Re: G4 problem?

Post by keithr » Thu Feb 26, 2015 7:18 pm

I did the Peggie with G4 a number of years ago and did not put anything on top as she looked good as it was.


Now beginning to discolour along the lines of tank joins under deck so sure this is damp from below as I store her upside down in the winter in the barn.

Plucking up courage to see if I can get away with just stripping affected areas and re-applying G4.

Has anyone filled in bits before??. It used to work with Deksolje on Hobbitt.

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Re: G4 problem?

Post by Ed » Fri Feb 27, 2015 1:48 pm

My experience of patching G4 has not been so good.

It seems to darken with time (uv) and the new GV will not have darkened so looks lighter. However, this difference does get better as it darkens down....again over time. But, physically, it seems to patch-in OK... so as long as you don't mind the visibility of the repair you may be ok.

Seems to me the only thing which patches in easily or well are the traditional single pack varnishes. Especially the darker ones.

eib
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jonh
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Re: G4 problem?

Post by jonh » Fri Feb 27, 2015 6:55 pm

As recommended, I scraped a small section of the deck to establish whether the damp was between G4 and varnish or under the G4 itself. The attached photo seems to show that the damp is between the deck and the G4. What do you think?
Attachments
IMG_20150227_121032971.jpg
Photo of water damage to side decks
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