What to use for a Barrier coating... on a freshly-sanded gelcoat bottom?

[SkipperCanuck]

I have just stripped the bottom of a 23' O'Day sailboat hull down to the bare gelcoat. There was no osmosis, but the old antifouling had become an eighth of an inch thick and was patchy, rough and unsightly. I used a putty knife as a scraper to peel off most of the loose UNIPOXY, and then power-sanded the whole thing fair and smooth with 100 grit garnet paper, working until I saw the white of the gelcoat just beginning to appear.


Two and half days of really dirty work later, cramped under the boat hull in a respirator mask and a chemical suit, I had the bottom cleaned. Then I realized that I had better do something to seal the gelcoat, before the anti-fouling coating was applied, so as to prevent possible future osmosis or other damage from water being absorbed.

There were a few hundred small dings and scratches in the gelcoat before I sanded it, and some were deep enough to expose a bit of the fibreglass underlay, so I filled and faired those with a marine-grade waterproof two-part epoxy paste.


I now have on hand, 128 oz of WEST system epoxy #105 resin and the #206 hardener (but the WEST literature says that it will take 4 or 5 coats for an effective barrier, and that I must also mix in an additive, a barrier compound #4220, so I will need another two or three gallons of resin etc, at an additional cost of at least $300.00.)


I have also got 128 oz of a two-part Interlux 2000 Barrier coating and that will only take two coats (and is supposedly a better barrier than the 5-coat WEST system epoxy with the 422 additive barrier). No extra costs.


I plan to antifoul-coat the bottom with the blue UNIPOXY cupric oxide ablative paint, after I barrier-coat , in either case. The trouble is that it is SO much work to strip the bottom right down to gelcoat again I would like to get it right the first time.
.

So which barrier coating is the best ? The five (!) coats of WEST system epoxy with the 422 barrier additive (at about $300 in extra costs and two extra days work); or the two coats of the Interlux 2000 barrier (at no extra cost). I am leaning towards the Interlux 2000. It seems easier, it is cheaper and it may be more effective, or so the sales guy says.

I have no experience with either product, and who can believe sales claims? Any informed opinion would be appreciated.

[knottybuoyz]

We did the bottom of our express cruiser 4 yrs ago with the Interprotect 2000. No problems whatsoever. It went on well, got the desired thickness in the two coats recommended. Follow the directions from Interlux and you should get a good barrier coating. Get the good foam rollers that are safe to use with solvents. The epoxy will eat the cheap ones and you'll spend an hour pulling pieces of foam out of your paint. Don't ask me how I know that! Good luck.

[Alan Wheeler]

As Rick said. The Interprotect is good stuff.

Don't ask me how I know that! Good luck.

I don't need to ask, I have already been there done that myself. :-) Great to see you back mate.

[Terra Nova]

Originally Posted by SkipperCanuck

..
I now have on hand, 128 oz of WEST system epoxy #105 resin and the #206 hardener

I have also got 128 oz of a two-part Interlux 2000 Barrier coating and that will only take two coats (and is supposedly a better barrier than the 5-coat WEST system epoxy with the 422 additive barrier). No extra costs.

I plan to antifoul-coat the bottom with the blue UNIPOXY cupric oxide ablative paint, after I barrier-coat , in either case. The trouble is that it is SO much work to strip the bottom right down to gelcoat again I would like to get it right the first time.
.
So which barrier coating is the best ? The five (!) coats of WEST system epoxy with the 422 barrier additive (at about $300 in extra costs and two extra days work); or the two coats of the Interlux 2000 barrier (at no extra cost). I am leaning towards the Interlux 2000. It seems easier, it is cheaper and it may be more effective, or so the sales guy says.

I have no experience with either product, and who can believe sales claims? Any informed opinion would be appreciated.

Yo Nuck,

in your heart you already know which is the best system. But there are practical issues as well. After discussing my proposal with the technical person of both Gougeon Brothers (W.E.S.T. epoxy) and U.S. Paint (I believe for Interlux), I would apply all the material you possess, in an approved manner.

If I were not concerned with having a "racing" bottom, but just wanted it to be long-lasting, I would first apply all the thickened, barrier-additive-filled, catalysed resin, planning its' application such as to use the entire amount evenly. Once that coat has "tacked", I would apply all of the Interlux barrier coat in the same way. When this application has also tacked, I would apply three coats of the bottom paint. ALL coats wet-on-wet. You must qualify this with the suppliers.

This process depends greatly on technique and timing. It can save A LOT of work, if done carefully. It is an immense benefit to have a competent helper to roll and tip. Your success will come from your own due dilligence, with regards to the compatibility of the products you have chosen, and the recommended application techniques, and any necessary additives (accelerators, reducers,etc.) In hot weather, it is usually wise to do this work very early, or to shade the boat and materials at least. If for any reason a coat is allowed to dry, it must be washed and sanded before continuing, so it is best to be well prepared.

best, andy

[Alan Wheeler]

If for any reason a coat is allowed to dry, it must be washed and sanded before continuing,

Don't get confused between Epoxy Resin and Epoxy Paints. They are very different products.
With Epoxy paints, Each coat MUST dry. FOLLOW the Instructions. You will be given a minimum and maximum recoat time in relation to temperature. Ensure that you recoat within the suggested time. Too soon and you have too much solvent trapped in the paint. Epoxy paint has a very unique property. The solvent keeps the crosslinking from happening. You will notice that a thin film will harden much much faster than a thick one with epoxy paint. Infact, in some products a mixed tin can last 12hrs or so and yet dry time once applied maybe just 1hr. Solvent trapped in the under lying paint can also make the paint porouse and subject to water.

[SkipperCanuck]

Thanks to all of those among us who have replied, in such helpful detail.

I am going now to try to sort and assimilate all of what you have said and report that back to you, for an accuracy check.

Hmmm...bottom coating seems to be a master's level chemistry and physics study. I had NO IDEA it was so complex, and so now I am a bit intimidated. I still have no clear decision formed in my mind.

Time for an analysis of what I think I have been told. Please bear with me, I can use the help.

I summarize my (halting) understanding thus:

The pros and cons of using the WEST system barrier epoxy concoction are:

1). a good, hard and sometimes durable coat that is
2) hard to apply correctly (in five coats) owing to the somewhat critical timing issues as the resin cures, and the risk of trapping unpolymerized resin by early overcoating
3) the possible need to re-sand between over-cured coats. (Re-coat too soon and you get trapped liquids that never cure...and osmosis. Too late, and you gotta re-sand or the coats do not cross-link at tyhe molecular level.)
4) Any over-coating has to be applied within a correct time frame also, and there may also be solvent compatability issues.
5) Timing, cost and chemistry. Can be tricky to get it right, get it wrong and time, cost and labor are wasted. It is expensive, about 4:1 compared to interlux 2000 for cost and 6:1 for labor.
6) Risk of trapped solvents inviting future osmosis is appreciable.

That seems clear enuff. Epoxy is however, very tough and strong stuff. Done right, it lasts forever, IF it is not damaged and is UV protected.

7) that IF seems to be the differentiating issue, because

8) Boat hulls always suffer impacts and fully-cured epoxy is a somewhat brittle substance, the thicker, the more brittle.

9) Stress and impact crazing is the biggest enemy here, I think.

10) Therefore here endeth the argument for epoxy without an over-coating , applied someday, if not at the time of epoxy application. Cross-linking of the molecules of the coating substances with the epoxy seems to argue that it should be over-coated sooner rather than later. IE Now, or not at all.

11) Tricky, expensive and fragile. Not a sure thing for a cack-handed backyard DIY guy like, maybe , ummmm.... me.

Enter the Interlux 2000 epoxy-paint barrier argument:

1) It is said to be quite effective in practice, it is easier to apply over a sanded gelcoat, and not quite so critical as to the re-coat application timing issue, but there is a timing factor.

2) A good product, but only if the manufacturer directions are followed carefully.

3) Not so brittle, not so thick, and not so expensive, nor so labor-intensive as WEST system barrier epoxy.

4) Experience related by users bears out its effectiveness as being very good, the equal of WEST barrier epoxy.

5) There are no issues with gelcoat compatibility, but there may be, with some anti-fouling coatings.

6) There is less danger of trapped epoxy solvents later absorbing water, if the paint is applied according to manufacturer directions.

7) More durable than epoxy owing to the thinner coat being less susceptible to stress crazing. (Surprises me to conclude that!)

My conclusions, as predicated upon the foregoing understandings being substantially accurate, is that Interlux 2000 is easier, better, cheaper, more durable and therefore more effective (because of the stress crazing issue suffered with the required multiple (5!) coatings of WEST epoxy barrier). Apologies to the GOUGEON Bros.

SO therefore, a decision:

Barring any serious disagreement from my better-informed colleagues on this forum, I guess that I will

1) apply only the 2 coats of Interlux 2000 product, directly over the gelcoat, (as prepared and patched with epoxy paste,) and save the epoxy resin for building or repairing something else, if I ever get the time.

2) I will overcoat that Barrier coat with the UNIPOXY anti-fouling paint, for this year.
3) Next year I will re-evalute the antifouling stuff again.

What say, good friends, any concurrence?

[irwinsailor]

We used WEST system on our boat 5 years ago. We did 7 coats (about 10 gallons) and it turned out very well however if I could do it again I would use the Interlux system for its ease of application.

[SkipperCanuck]

I appreciate that reply, Irwinsailor. Nothing beats experience. I agree that ten coats of epoxy is a really good job, but you do seem to concurr that it is a long and difficult, and perhaps an unnecessary expense of time, effort and money.

I note the approving comments and the experiemce of those who have used the Interlux 2000 with equally good results. I daresay that you agree with my decision. I am now a bit more easy in my mind about it.

Tuesday is barrier-coat day, weather permitting.

Kind regards

[Terra Nova]

[quote=SkipperCanuck]

The pros and cons of using the WEST system barrier epoxy concoction are:

1). a good, hard and sometimes durable coat that is
2) hard to apply correctly (in five coats) owing to the somewhat critical timing issues as the resin cures, and the risk of trapping unpolymerized resin by early overcoating
3) the possible need to re-sand between over-cured coats. (Re-coat too soon and you get trapped liquids that never cure...and osmosis. Too late, and you gotta re-sand or the coats do not cross-link at tyhe molecular level.)
4) Any over-coating has to be applied within a correct time frame also, and there may also be solvent compatability issues.
5) Timing, cost and chemistry. Can be tricky to get it right, get it wrong and time, cost and labor are wasted. It is expensive, about 4:1 compared to interlux 2000 for cost and 6:1 for labor.
6) Risk of trapped solvents inviting future osmosis is appreciable.

That seems clear enuff. Epoxy is however, very tough and strong stuff. Done right, it lasts forever, IF it is not damaged and is UV protected.

7) that IF seems to be the differentiating issue, because

8) Boat hulls always suffer impacts and fully-cured epoxy is a somewhat brittle substance, the thicker, the more brittle.

9) Stress and impact crazing is the biggest enemy here, I think..
quote]

Yo Nuck,

how you choose to coat your hull is entirely up to you, but you have made so many dreadfully inaccurate assumptions here that I must at least comment.

a) The W.E.S.T. coating is extremely durable and flexible, not subject to crazing, and not brittle as you have somehow imagined.

b) There are NO solvents or other liquids to become trapped; one does not "thin" W.E.S.T. epoxy.

c) There is no unpolymerized resin. You simply mix parts A&B as with any two-part system. Once mixed, it will cure. It does not require exposure to air, therefore it is quite impossible to have "uncured" resin.

d) You don't have enough material to do 5 coats, so there is no appreciable difference in labor.

e) You already have the material, so there is no extra cost involved.

f) There is no critical chemistry (mix 5:1), or timing--you just don't wait hours for it to cure completely between coats.

best, andy

[SkipperCanuck]

Andy..appreciate the corrections to my assumptions. Last question: Why is WEST epoxy better than Interlux 2000, all other things being equal?

[Terra Nova]

Originally Posted by SkipperCanuck

Andy..appreciate the corrections to my assumptions. Last question: Why is WEST epoxy better than Interlux 2000, all other things being equal?

Yo Nuck,

hardly anything in life being equal, let me first explain that I have no experience whatsoever with this new 2-coat-miracle Interlux 2000. But I have 30 years of experience with the W.E.S.T. system, which has been generally regarded as the accepted industry standard repair platform and barrier coat since the University of Rhode Island discovered what caused the osmotic blistering--possibly preceding that discovery.

What I have concluded from my own personal experience as a boatbuilder, as well as my own observations while living and working on the water during that thirty years, is that there is no other product which has so successfully proven itself to industry professionals and boatowners alike. This experience has had to do more with the correction, and subsequent prophylactic, of a blistering problem for affected yachts, rather than strictly as a preventative measure on a new or unaffected hull.

I do not discount the possibility that I might be completely unaware of the existence of some new easy-as-pie wonder cure.

best, andy

[SkipperCanuck]

Andy, you speak from long experience. Very hard to disagree with what you said, and in fact, I have no reason to disagree with you. I have no experience with either one of these measures.

I do not see any evidence of osmosis in the hull of my ODay and so I do not seek a fix, but a preventative barrier coating. You are certainly in good company as to the recommended cure for existing osmosis, about which I have done a bit of reading. From that reading, I learn there really is no better way to fix osmosis than that procedure of removing the damaged gelcoat down to the fibre, and then replacing it with many coats of WEST system epoxy combined with the 420 additive. It is the most accepted practice that I have seen in the literature.

In reading further, I have also learned that epoxy forms only a mechanical bond with a fully-cured gelcoat, and the strength of that bond depends upon being set up on a roughened surface. I think that you will agree that gelcoat, which is usually a polyester, has a much different modulus of elasticity than does WEST system epoxy. The implication of that fact is that when the two layers are sharply flexed, such as in an impact, one of the layers will be distorted more than the other. I think, and my reasoning comes from the observation that it is usual for the epoxy overcoating to crack, in such a case. I also reason that this is because the part of the epoxy coating furthest from the center of impact is usually on the outside of a radius formed by the lays of the glass-reinforced epoxy covered by the polyester gelcoat. Since the outer layer is not glass reinforced, and since it has only a mechanical bond with its supporting gelcoat, it is the weaker part of the matrix. Fully-cured WEST epoxy is not a very elastic substance and so it does not stretch, therefore it must crack. The cracks admit water to the gelcoat.

I do agree that if the gelcoat is first removed, then the applied epoxy will form a very strong bond with the repaired fibre lays, and that makes all the difference. I believe that this difference is why such a rfepair is the best one, and why the idea of a barrier coat is another kind of situation.

I dunno which is best, but I do know which is easiest..and others who have used Interlux 2000 say that it is a good product for its intended purpose. I will sleep on it some more.

Thanks for the carefully explained and valid explanation.

Just an opinion, Andy.

[Terra Nova]

[quote=SkipperCanuck]

I do not see any evidence of osmosis in the hull of my ODay and so I do not seek a fix, but a preventative barrier coating.

Fully-cured WEST epoxy is not a very elastic substance and so it does not stretch, therefore it must crack. The cracks admit water to the gelcoat.
quote]

Yo Nuck,

since you have seen no evidence of any osmosis, your's seems a good candidate for the simple system.

The cured epoxy resin is much more flexible than polyester resin. This is why it has proven so successful as a barrier coat. While I frequently see gelcoat stress cracking, I cannot recall ever seeing this with W.E.S.T. epoxy.

Also do not underestimate the superior tenacity of a secondary bond using epoxy.

best, andy

[Boracay]

Some epoxys will display an amine blush (a "water soluble?" waxy surface) on curing which must be removed before overcoating.

If the coats are applied wet on wet this may not be necessary.

I have found the thin films of the 5:1 generic epoxy that I use are very flexible.

Thick coatings (3mm+) will crack if provoked sufficiently.

[CSY Man]

All this discussion and all the opinions about a 23' O'day sailboat..?

If this was my O'day I would clean with acetone, then slap on a coat of West 105/206.

A barrier coat of something, then bottom paint.

If it was a $400,000 boat, I would be a bit more careful as big money was a stake, but for a little day sailor, I would finish the job in a day or two, then go sailing.

Did pretty much the same thing on my boat 2 years ago:
Found a bunch of micro blisters on the haul-out.
The yard manager was wringing his hands and talking about the need for a strip and blister job and the 2 month dry out period, etc, etc.
He even proved it with his moisture meter...The hull is soaked, ya are in deep trouble, blah..

Truth is: Within a few days of hauling, the bottom paint has enough moisture trapped to give a high reading on the meter..He knew it but tried to Bullzhit me.
(Stay away from a certain yard in Ft. Lauderdale, PM for details)

I called my surveyor-man to get a second opinon on the micro blisters.
He came by and said they were just gel-coat blisters, nothing wrong with the hull or the glass.

Sanded the paint and the gel coat. Used West epoxy on the affected areas. (Not a big deal, the hull on my boat is 1 and 3/8 inch thick, no compromise as far as osmosis or blisters in the hull, just the gel coat)

Then slapped on the equivelant to Interlux 2000. (Petit makes the same stuff, just a different name)

On top of the barrier coat, 2 coats of Petit Trinidad Blue.

2 years later, all is good.