To Gel or Not to Gel - That Is the Question

[s/v Jedi]

David,

I know epoxy quite well. It is actually not a matter of agreement... your info is incorrect. I know you won't believe me although I provided a source you could have used to confirm my statements. So, I will quote from that source.

=> West System, Final Fairing and Finishing guide, page 15:

Make sure the previous coat has cured firmly enough to support the weight of the next coat. The ideal time to recoat is when you can still leave a finger print in the previous coat, but it will no longer come off on your finger. Epoxy will chemically bond to a previous coat of epoxy that has not fully cured. Fully cured epoxy must be prepared by washing and sanding to achieve a mechanical bond with the next coat.

Now, if you know anything about epoxy, you understand that a chemical bond is always stronger than a mechanical bond. In fact, with a mechanical bond you also have chemical bonding within the layer thickness of the applied epoxy.
Another big reason for not doing mechanical bonding is the prep and the risk of not doing that right in spots or contamination. You completely avoid that risk when taking the chemical bond approach.

On UV: Colored paints are protected by the pigment. Sorry, but that's just the way it is. There might well be some UV absorber added to the paint, but it is the pigment that does 99% of the UV protection. That is why a paint lasts so much longer than a varnish.

You are of course right that you need more protection for the final finish than some pigment added to the epoxy. I explicitly wrote that the pigment is for temporary protection only. But, just for common sense, normal gel coat is just pigment with a binder, without UV filters. Adding the West System white pigment for temporary UV protection is a technique used by West themselves.

So, for your convenience, I quote from the same publication, page 17:

Any coating that adhered to the surface and contains enough pigment will protect the barrier substrate from UV, for a time. Pigmented coatings work because opaque pigments reflect both visible and ultraviolet light before it passes through the coating film. Clear coatings and varnishes, on the other hand, are designed to allow light to pass through the film to the substrate and back out. They depend on "ultraviolet absorbers" to selectively trap radiation in the UV wavelength in the coating before it reaches the barrier substrate.
[...]
UV absorbers alone are not as effective as pigments in blocking UV. Consequently, even the best clear coatings do not last as long as pigmented coatings, and require more frequent recoating.

This is exactly how I wrote it I think. What this doc doesn't state is that the UV absorber is actually "used up" while absorbing UV. That's why even the best varnish fails. For a pigmented paint or gel coat, polishing helps because only the outer surface is degraded by UV, with fresh material underneath. For the same reason it's better to strip all varnish instead of just sanding a bit.

I would really recommend to read the documentation provided by the manufacturers. It really helps to have the right information.

cheers,
Nick.

[Christian Van H]

It should be fairly obvious that the first coat of epoxy over a raw fiberglass hull will be a mechanical bond. Duh. It should also be obvious that the sanded, porous bottom would have an incredible amount of "tooth". You know, the micro ridges and pores that the first coat will bond with. Now, coat the whole hull with shiny plastic and seal up all those ridges and pores. Thats what you do with your first coat of epoxy. If you let it harden completely before applying the next coat, the only bond will be mechanical with what ever tooth you create by once again roughing up (why on earth would you want to remove epoxy you just applied as a water barrier?) the first coat. "Hot" coating creates a MUCH higher PSI bond, with less work. Duh again. Want to see how well epoxy bonds with shiny plastic? Mix up a couple squirts in a plastic cup and let it go off. Should take you all of a few seconds to pop that baby out. THERE IS NO REASON TO WAIT FOR FULL HARDENING AND SCUFFING BETWEEN COATS USING MODERN NO BLUSH EPOXIES! None. Unless, that is, you'd like to make a full size replica of your hull. In that case, let the first coat harden, do a bad job with the scuffing, and with any luck the next six coats might pop off by themselves. TA-DA! Full size hull model!

[Fishman_Tx]

Ok,.. ANYWAY, ..........
Let's go back to fillers, shall we?
As it stands, the (West System) documentation calls for 407 low density or 410 micro-light fillers for fairing (after 1 full coat). As far as I can see, moisture penetration to the filler thru 7-9 layers of epoxy (almost 20 mils), and let's not forget the ablatives, under normal conditions is unlikely at worst to damn near impossible at best. If done properly, ("green" applications w/422 barrier additive) I find it highly unlikely that the filler type would make any difference at all except in sandability. Everyone has their preferences as to what they use, but honestly, can anyone cite an occasion where this occured in a bottom job (specifically)? I am not trying to provoke anyone or "dis" their preferred method. I was just wondering......

Now on deck repairs I agree, go with the hard sh*t irrelevant of recommendations as it doesn't get all that extra protection of over coating.

[Fishman_Tx]

And, BTW we still haven't decided which epoxy system to go with yet....

So far, the Interlux is leading....

[Stillraining]

Great reading
I wish you the best of luck Fish.


I for one am a little nervous for you...personally I would have pealed the hull...I see you doing all this hard work and having other areas continue to blister on you...My best wishes in hopping that does not happen.

[Solitude]

Fish: another thing about the Interprotect ..... I was told to make sure mix it often the (micropallets ) are heavy and sink quickly.

[Fishman_Tx]

Originally Posted by Stillraining

Great reading
I wish you the best of luck Fish.


I for one am a little nervous for you...personally I would have pealed the hull...I see you doing all this hard work and having other areas continue to blister on you...My best wishes in hopping that does not happen.

No need, tho it would have done a smoother job on the gel than my grinder. All the gel below the waterline is gone, at least on one side, haven't got to the other side yet. Don't believe the pix! They're the old ones! All that you see is gone. I used those to illustrate the size of the blisters. All large, no popcorn.
Nope, all the gel below the line is going bye-bye. Starboard side is down to the chop and past in some places. Large blisters only and no significant delam, on THIS side. Now the port side is a different story. There is an area on the lower part of the keel that sounded off during a hammer test like delam. A dull flat slapping sound. Thank God it's on the lower keel and not in the transition. Hell, I wanted to see my lead weight ballast anyway.
But we're not to that area yet. Trust me when I say we're doing nothing half-assed. It's the whole ass or no ass at all.

[Stillraining]

Cool!

Just to clarify ...when I say peal the hull I'm meaning removing all mat to the roving.

Sounds like your doing that as well for the most part...It think you are very smart in doing so.

Look forward to reading more of this story to come.

FWIW...I have repaired two blisters on my hull that were 2" in diameter once past the mat which was pretty dry looking and unsaturated the roving was a solid as a rock translucent green and very smooth and shiny...I personally would not care if the whole kit and caboodle just fell off in one piece below the water line down to it.

[s/v Jedi]

Originally Posted by Fishman_Tx

As it stands, the (West System) documentation calls for 407 low density or 410 micro-light fillers for fairing

Okay, 407 is micro balloons... stay away from that. So you get to the 410 micro-light. That one is sensitive to heat. No problem under the waterline as long as the boat is in the water. On the hard, with black (or other than white) anti-fouling in the sun, you take a risk.

I know you don't want to hear this so let's make a compromise: use a 50/50 mix of micro-light and colloidal silica for the fairing.

cheers,
Nick.

[Fishman_Tx]

Originally Posted by Stillraining

Cool!

Just to clarify ...when I say peal the hull I'm meaning removing all mat to the roving.

Sounds like your doing that as well for the most part...It think you are very smart in doing so.

Look forward to reading more of this story to come.

FWIW...I have repaired two blisters on my hull that were 2" in diameter once past the mat which was pretty dry looking and unsaturated the roving was a solid as a rock translucent green and very smooth and shiny...I personally would not care if the whole kit and caboodle just fell off in one piece below the water line down to it.

Ah! Gotcha, I had a sneaking suspicion that might be where you were going. Actually, there is very little chop at all. This hull is pretty thin. Honestly, I think that's what bugs me the most; how thin the hull actually is.

[Fishman_Tx]

Originally Posted by s/v Jedi

Okay, 407 is micro balloons... stay away from that. So you get to the 410 micro-light. That one is sensitive to heat. No problem under the waterline as long as the boat is in the water. On the hard, with black (or other than white) anti-fouling in the sun, you take a risk.

I know you don't want to hear this so let's make a compromise: use a 50/50 mix of micro-light and colloidal silica for the fairing.

cheers,
Nick.

Sensitive to heat? You mean like a high expansion coefficient? i.e. plugs of filler popping up?

AACCHH!!!
http://www.seqair.com/skunkworks/Glues/Notes/Notes.html

"I have been informed by Brian Knight of Gougeon Bros that the filler is probably going to be OK in the temperate climate of the UK, if I were to paint my Falco red. However, he did warn me that if I were to fly my aircraft to, say, the Mediterranean or wherever the air temperature exceeded the 70-80°F range, I could expect the sanding marks left by the rubbing-down process to show through the paint or, even worse-where there is a substantial thickness of Microlight filler-a swelling of the filler could occur, because the filler is a thermoplastic material. Only light colors would overcome this problem." Glass and phenolic microballoons are not affected in this way.

Crap again!

Phenolic Microballoons
The heading microballoons is a generic term we use for microscopic hollow spheres. These spheres, typically 50 microns in diameter, are filled with air and actually displace a large amount of resin and because of their lightness are far superior to chopped strand glass fibre. Phenolic microballoons (~250 g/litre) are a specific type easily recognised by their reddish-brown colour; their softness makes them ideally suited for wood fillets, i.e. they sand like wood mixed in the correct proportion. These are not particularly waterproof so are no good for model boat hulls.

[Fishman_Tx]

So what the hell is one supposed to use that will DO THE JOB but not be harder to sand than the fiberglass ?!?!? Milled Fiber?

[s/v Jedi]

Good to see you found the problems with these fillers yourself ;-)

Like I wrote "50 posts" ago: colloidal silica (Cabosil) filler.

cheers,
Nick.

[Fishman_Tx]

Originally Posted by s/v Jedi

Good to see you found the problems with these fillers yourself ;-)

Like I wrote "50 posts" ago: colloidal silica (Cabosil) filler.

cheers,
Nick.

I know you did, but dang I didn't want to spend the next 6 months sanding

[Maine Sail]

Originally Posted by Fishman_Tx

I know you did, but dang I didn't want to spend the next 6 months sanding

Trust me it is NOT as hard as some would have you believe. When mixed with milled fiber it actually sands quite well. And even alone it sands well..

I hope with all the sanding, if you remove actual fiberglass cloth, mat or roving that you will be replacing it not just removing it and going over it with a barrier coat.?