Epoxy Hull Treatment - Any general advice?

seanfoster

seanfoster

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I'm just about to start the restoration of my new Dufour 1800 (and there's some work to do believe me!)

The boat has been sitting out of the water for over 4 years, and the hull is in remarkably good condition below the water line. I was wondering whether to apply an epoxy protection layer to reduce the risk of future osmosis, it's something I've never done before (or even looked at) could anyone with experience in this area give me a few tips regarding good but cost effective systems, good supplers any tips for application?

Should I apply protection to the (cast Iron) keel? I've heard that cast Iron can absorb upto 10% water.

Any advice would be welcomed!
 
I had the bottom and keel of our Oceanis 390 lightly sand blasted then a two layer 'shell' of epoxy resin and finishing cloth applied to the hull. Over that I have 6 coats of International VcTar2 epoxy primer. The VcTar sets much like a plastic bag, tough and flexible. The keel has 2 coats of standard epoxy primer.

I'm applying coppercoat over the whole hull below the water this season because the boat is dry sailed and I don't want to hassle with anti fouling.
 
Some years ago i bought an Anderson 22 that had been out of the water for ten years, i epoxied her with an industrial 2 pack epoxy pitch from Witham paints of Lowestoft, same spec as VC tar but way cheaper.
 
Did my last boat 3 years ago. The procedure was first to check moisture in the laminate - needs to be below 5 on the appropriate Sovereign scale. You can hire a moisture meter from "passion fo paint" . Google it.

Then you need to clean the hull thoroughly. No remaining anti foul. Abrade the surface if you have scraped it clean. I use the Farrow system and was very pleased with the result.

The application of the Blakes solvent free I used was easy enough but you really need 2 people. One to roller the epoxy on and a second to mix the stuff in the first place and then to lay oiff with a brush after rollering. I didnt have the second person so ended up with the same sort of dimples you find on a golf ball surface. Quite fetching really.

Thge epoxy needed to be applied on a dry warm spring day.
 
I think it would be wise to epoxy the bottom at this stage. You should look on it as an insurance policy as you cannot know if it will be necessary, nor can you know if it will work as the seeds of osmosis could already be in place. Having said that she should be pretty dry after 4 years out of the water so it's the right time to do the work unless water has been sitting in the bilge in that time.
Unless you need to do it now I suggest you wait until summer / autumn as the temperature will be consistently higher, making the work much easier. If you want to get moisture readings hire a meter from Nigel at Passion for Paint or get a friendly surveyor passing through your yard to run some checks for you in exchange for a few beer tokens. You should look for differences above and below the water line as the key indicator. Absolute numbers don't mean a great deal in isolation. Again, if water has been sitting in the bilge, dry it out and wait a couple of months with good ventilation before doing the checks.
If the hull is in good condition I would recommend a solvent containing epoxy rather than solvent free. Easier to apply, more tolerant to weather conditions and more tolerant to temperature changes during application. Any of the products from a marine manufacturer are good and generally designed for DIY application. There will be plenty of other good (and cheaper) non marine products but they may not be so easy to apply. Aim for 300 - 400 microns dry film for a good moisture barrier.
Treat the cast iron keel differently. If there is any sign of rust breakdown this will be the best time to correct it as it should be reasonably dry already. Get it dry blasted to a good standard and as soon as possible after blasting apply a good zinc rich primer, working it well into voids and pits. Put 2nd coat of zinc on then build up with intermediate coat of primer suitable for the zinc primer. This will give a much more durable finish than just using a pure epoxy as it give active protection rather than passive. Cast iron will be corroding as you look at it and it is virtually impossible to remove that corrosion completely. A pure epoxy will hold it back for a while but cannot stop it. Zinc has a much higher chance of stopping it.
Hope all goes well and you're on the water soon.
 
Thanks Pasarell for your reply, (And eveyone else) that's exactly the sort of info I was after. I doubt the boat will be in the water this season as there's a lot to do, but I think it makes sense to do this at this stage, and will wait till the summer to do it.
 
Pasarell reminded me - make sure you check with a meter cos if the hull isnt dry after a few years out of the water then thats a good indication that there is osmosis. Its a bit like a jar of salt - if you leave that with the lid off it will never dry however long because its hygroscopic. The osmosis products are the same.

And there is no point whatsoever in coating a wet hull. To the contrary, you will make the blister problem worse when it arrives because you will have trapped the moisture in the laminate even more than was the case with the original gel coat. And you will have wasted money.
 
G'day Sean,

If you are not planning to remove the gelcoat prior to applying osmosis protection of any sort, forget, it could cost you a small fortune for no reason.

The gelcoat has to be removed to confirm osmosis or wicking has started, I would advise you to either do nothing, because you may be sealing a problem in and causing more problems: or wait till you see some signs of problems.

As for the treatment of a cast iron keel, keep the following in mind.
Cast iron is porous and in a marine environment may also have a high salt content, So dry blasting is important.

Any method involving sanding or grinding will only spread the contamination into the many small voids, a constant flow of clean blasting grit avoids this problem.

Cast Iron will 'flash rust' in seconds, so getting a protective coating on as soon a possible is critical, I use a roller on a stick and follow the blasting nozzle.

The first coat should be a high zinc paint. However take care and read the manufacturers instructions, most zinc paints have a fine dry thickness tolerance, too thin it wont last, may not even work, too thick and will mud crack giving no protection at all, most are around 70 microns, but read the tin.

Next apply your epoxy, at least 2 coats with a roller and tip off with a long haired brush 2 to 3 inch wide. Note, temperature should be above 18c and humidity below 74% for most marine epoxies.

Next, fair the keel with a mix of 'closed cell' micro balloons and epoxy resin
applied with a flexible straight edge, a plastic ruler or the an old strait backed hand saw, both will reduce the amount of sanding required after curing.

Do not start sanding till the resin has fully cured, 24 hours if warm and dry longer if cool or high humidity. Wash the keel with a running hose and fresh water, rub it with a plastic 'scotch-brite' kitchen scourer, start at the top and work down, when the water no longer forms beads you have removed the residue left by the curing process, sanding it without washing first will only spread the contamination.

After sanding to the required shape, apply at least 4 coats of resin with a roller and tip off as before.

After curing wash as above and give the epoxy a light sanding with a 200 grit on a block. you only need to remove 50% of the high gloss.

Next, after cleaning apply a coat of high build epoxy primer, a mist coat, then a half coat, then a full coat, leave the paint to tack off between coats.

You can now apply any 'extra' protection you think you might like, we have used the industrial pylon paint as used on steel jetty constructions in harbours with good results.

I hope this helps.

Avagoodweekend......
 
There's good advice here - but be warned about the amount of effort needed to complete such a task, assuming the hull is in good nick for treatment.

I have done this once to a 32 ft boat, and would never undertake it again. Just removing all debris and cleaning to the appropriate standard is a major undertaking. Grit cleaning is the best way - well worth it.

Application then depends on settled warmish weather to repaint whilst a key remains open, and that includes the first coat of AF to be applied - potentially 3 days of work just right there.

Keels can be faired then primed heavily, but as said, no system will keep the iron material rust free indefinitely. Adjust your expectations, and then the amount of effort and paint you apply!

As to whether gel shielding is worth the effort, I think it more marginal today than in earlier times when osmosis sounded the end of a boat's trustworthy life. Anything built within the last 8-10 years is built with a much better understanding of materials and layup methods. Debatable...

PWG
 
I wonder what to apply to used wooden boat, dried out, as coating for strength and reduction of maintenance?
 
[ QUOTE ]
I wonder what to apply to used wooden boat, dried out, as coating for strength and reduction of maintenance?

[/ QUOTE ]

G'day boatyjan1, and welcome to the YBW forums.

Your question is a bit off topic and well down the list of postings, I would think you will more responses by asking the same question in a new thread.

Avagoodweekend......
 
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