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Old 07-03-2016, 12:30   #16
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Re: Osmosis prevention for oldboat

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Believe it or not, I don't think you can get a more proven range of products than Sherwin-Williams (they have very extensive offshore experience with a range of well proven products).
FWIW, the Sherwin Williams line of anti fouling paints are inferior, IMHO. If it's me shopping for a barrier coat, I go with a company that specializes in marine coatings and has a decades-long proven track record, like Interlux.
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Old 07-03-2016, 12:47   #17
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Re: Osmosis prevention for oldboat

For me I stripped off all the old anti foul, sanded and did some fairing, figured it is cheap protection why not. My boat didn't have a blister on it after 40+ years want it to stay that way. Certainly cheaper than dealing with a case of boat pox.
Learned long ago there is no point in tormenting yourself over boat maintenance costs and you are better off spending a little now than a lot later.
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Old 07-03-2016, 12:55   #18
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Re: Osmosis prevention for oldboat

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I replaced the Interlux 2000 Barrier with Sherwan Williams. The Interlux was applied by the builder and failed on the entire hull in less than 8 years. It actually resulted in increasing the hull blistering because it tended to trap moisture. Word at the yards around here is that it generally fails in about 5 years. It's been 9 years since the SW was applied and not a single sign of moisture in the hull. The SW product identifiers on the 1 gallon Part A & B cans are: Epoxy-Polyamide, Type III, Formula 150, N1V00350, 640182580 (Part A), 640182168 (Part B). It also has a mil. # Mil-DTL-24441D/20A & 20B Paint. You can get it at your local SW store or they can order it for you. Just make sure that the hull is dry and any blisters have been rectified. Hope this helps.
Oh it sure does! Thank you so much!

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Learned long ago there is no point in tormenting yourself over boat maintenance costs and you are better off spending a little now than a lot later.
Amen!
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Old 07-03-2016, 16:59   #19
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Re: Osmosis prevention for oldboat

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1970 boat, heavy hand layup (almost 1" thick throughout the hull), life spent in cold Northern waters, hauled each Autumn for inside storage.

No osmosis, and might not even get any. But prevention is better than cure, right?

So I did a search of the forum, and came across a recommendation for Sherwin-Williams two part barrier coat, and looked into it, and it seems they do some really good stuff (quite a range, in fact).

Epoxy Coating Comparison Chart - Sherwin-Williams Protective & Marine Coatings

So anybody used it? Which one did they use? How many coats? Where did they buy it?

If no info available, I'll contact the Company (though first hand user info is best) and update if I get a response.
Interprotect 2000E is one of the best. 2-part epoxy with mica flakes. You need to get down to bare gel coat - no antifouling. Good news - they recommend a rough surface for bonding so sanding or sand blasting is OK. We applied 6 coats.
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Old 07-03-2016, 17:03   #20
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Re: Osmosis prevention for oldboat

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Oh it sure does! Thank you so much!

Amen!
I use SW 'Tile Clad' white 2-part on the interior hull surfaces. Bright white & hard glossy. Makes the inside of lockers pretty nice and easy to clean.
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Old 07-03-2016, 17:04   #21
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Re: Osmosis prevention for oldboat

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Interprotect 2000E is one of the best. 2-part epoxy with mica flakes. You need to get down to bare gel coat - no antifouling. Good news - they recommend a rough surface for bonding so sanding or sand blasting is OK. We applied 6 coats.
As I will want to take it back that far for the CopperCoat anyway, something like that seems worth the relatively low extra expense imho.
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Old 07-03-2016, 17:51   #22
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Re: Osmosis prevention for oldboat

My boat is 32 years old and never exhibited an osmosis issue. After so many years the bottom was anything but smooth and every year there was a patch or two where the paint would lift off. I decided to scrape off all the old paint manually and then I used 80 grit paper and an orbital sander to finish the job. I put my winter cover on and the hull will have a chance to breath for four months. Soon I will apply 4 coats of InterProtect 4000e and a couple coats of ablative. I'll use two different colors so I can see where to touch up in the future. I'll have the smooth bottom I always wanted and the barrier coat is cheap insurance since I was bringing the bottom back down to the gelcoat anyway.

Here's a picture from last fall right after I had put the winter cover on.
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Old 08-03-2016, 09:58   #23
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Re: Osmosis prevention for oldboat

I've been reading up on this MIL-DTL-24441 spec barrier coat, and it's really good stuff. There's a Type III which needs 3 coats (for 9 mil total application thickness), and a Type IV which is for 2 coats (for 10 mil total application thickness).

I'm tempted by the Type IV I must admit.

This stuff is also good for bilges (don't let water into the layup from that side either), and inside potable water tanks.

Thanks for the insights all.

PS Interprotect also do this MIL-DTL-24441 spec too.
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Old 09-03-2016, 08:46   #24
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Re: Osmosis prevention for oldboat

With regards to applying Coppercoat to a previously applied epoxy, compatibility is not an issue as long as the appropriate over-coating windows are adhered to.

In simple terms there are two types of epoxy on the market, solvent-based and solvent-free. Either can be used for providing osmosis protection but have different characteristics, both when applying and when over-coating.

Solvent-based epoxies (such as Interprotect) tend to be thinner and easier to apply but therefore you need to apply more coats to achieve the required thickness. Being heavily solvented, you also need to allow these epoxies to fully cure before “sealing” them with any other epoxy, such as Coppercoat. This full cure normally takes about 7 days, depending on temperature. On the plus side, solvented epoxies normally cure to a leave a matt surface, so no further preparation is necessary before over-coating. However, it is best practice to lightly abrade the surface of cured epoxy to be absolutely sure of a good physical key.

Solvent-free epoxies (such as West System) are normally thicker and can be more difficult to apply, but take fewer coats to achieve the required thickness. One of the advantages of being solvent-free means that you can usually apply the Coppercoat whilst the solvent-free epoxy is still finishing its cure. This not only shortens the total time needed to treat the boat but also provides a good chemical key between the coatings. Of course, if a solvent-free epoxy is allowed to fully cure (and the over-coating window for a chemical bond is missed) it will leave a hard and glossy finish that will require abrading before any further coatings can be applied.
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Old 09-03-2016, 09:03   #25
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Re: Osmosis prevention for oldboat

Thanks Ewan!
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Old 10-03-2016, 07:47   #26
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Re: Osmosis prevention for oldboat

Squander Bucks is a 1965 38 ft Chris Craft and it too has had very little blistering over the years. It has lived in the water here in Florida for since it was first brought down from Michigan in the late 70's I believe.

However there have been a few that have developed over the 30 years I have owned her. Typically, each is ground out and refilled with epoxy based filler, faired in and the area plus a few inches all around covered with E-2000 - followed by my bottom paint.

About 10 years ago I had the bottom sandblasted back to gelcoat and two coats of E-2000 put over the entire bottom. Many people have remarked over the years when the boat is on the hard that the bottom looks really good when compared to some of the Hatteras and Bertrams that are in for blister jobs that are of new vintage.

Stick with covering the bottom with something that most boaters have an excellent track record with and you wont be a guinea pig to try and save a couple of dollars in the short run.
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Old 15-03-2016, 23:37   #27
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Re: Osmosis prevention for oldboat

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Much of the FG resins used in the early 70s have exhibited little or no inclination to allow for water absorption. If it ain't broke why in the world do you want to fix it? There must be other great projects on your boat on which to throw your time and money.
I was corrected on this some time ago, here on this forum.

I service boats in Lake Ontario, and I advise that if a boat was manufactured after 1995 (after widespread use of vinylester), osmosis prevention is not likely required. Additionally, if it was manufactured before 1995, and it is not showing any sign of osmosis now, it is not likely to be seriously affected in future.

EXCEPT, when taking a northern cool fresh water boat (e.g. Lake Ontario) into southern warm salt water (e.g. Caribbean, where some boats have been suddenly afflicted with severe pox, where none were before).

Now, if one is getting there bottom stripped, it is wise to apply a coat of primer (e.g. Interlux 2000E) before the new anti-fouling. If at the same time, one wishes a barrier coat (3 more coats of Interlux 2000E) the incremental cost is minimal, so why not?

Everything else being equal, a severe blisters (even small non-osmotic blisters) will knock about 15% off the boat value. A boat with a top condition bottom, will add about 10%.

For most boats, the value gain vs cost is in favour of the owner, (even when completely hired out at full yard rate.)

Putting a good bottom on, is actually one of the better boat investments one can make.

Disclosure: I sell and apply marine finishes professionally. This post is offered as free friendly advice and not intended to solicit business.
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