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Arjen 03-24-2013 08:34 PM

I'm going to do my bottom, but im new to this. Also, keep in mind we are talking about a 40 year old boat and money is an important consideration.

There are some scratches and things that look like a bit more than scratches on that need to be filled up. No osmosis, but just damage that goes deeper than the paint and whatever other top layers there may be. Some places, espescially on the bottom of the keel where you are looking at core layers of fibre glass. Other than that, layers of paint and/or gel coat that are bladdering off here and there. Finally, there is one area that has an extensive recent fibreglass repair. (a hole that was fixed) So there it is not the original material that after 40 years i can trust to not blister.

So i will need grind out those holes, fill them up with filler. Thats obvious. If there is no osmosis, how important is it to give it time to dry out and how much time would it need to dry out before i apply anything ? Note that i am in the a tropical climate with humid high temperatures. A am advised to use a mixture of fibreglass resin, fibreglass cut to small pieces and a white powder they name airofibre or something. Sounds good ?

Then comes the layers. I was advised by the shipyard to grind the whole bottom bare to the fibreglass, apply the filler, "paint" the whole thing with polyester resin, then apply barrier coat, then antifouling. Needless to say, this is a hell of a job and the barriercoat adds a bunch to the cost.
Some other boaters out here advised me to just put gelcoat (30$ a gallon right here) on the bare hull and then the antifouling.

Now i am wondering about some things. This is a 40 year old boat that is not blistering, meaning i guess the original fibreglass is good stuff. If i am to do as advised and paint the whole bottom with a cheap fibreglass resin (20$ a galon) do i not actually lower the quality of the top layer and thus possible create a blistering risk that never existed ?

If yes, would it be better, in the areas where there is no damage to sand away only the top layer of antifouling and leave any possible gelcoat layers that may be underneath and apply cheap resin ONLY to the damaged areas where i used filler ?

Then, how big is the difference between barriercoat and gelcoat ? Consider that the barriercoat they offer me is 150$ a gallon and the gellcoat 30$ a gallon. I dont know brandnames, but the price may give an indication of quality... (and for comparison of shop price, they will sell me westmarine 26% copper antifouling for 150$ a gallon
Will gelcoat be enough on a 40 year old hull that has never been blistering ?
It would of course be nice if i could spare a 120$ on using that instead of barriercoat, but more importantly, i read everywhere about the importance of the right processing and layer thickness when applying the barriercoat. I have no means of measuring that exactly, so i worry if i do this unprecise, if it will even be worth using it ? Besides that i wonder about the quality of the barriercoat also because the shipyard does not seem to recognise it as a very important product to prevent blistering, they were telling me the cheap resin layer is what keeps out the water and the barriercoat was initially called a "primer" to make the antifouling stick.

Finally, if the barrier coat is needed, would it be a pro to use gelcoat as well (its ony 30$ anyway....) and if so, which one first ?

Any advice is apreciated, thank you :)

Faster 03-24-2013 10:42 PM

Re: bottom
Barrier coat (usually an epoxy formulation) is required because gelcoat is not impermeable to water. Gel coat is not put over top of a barrier coat.

Boats that need it are taken back to bare glass, non-osmotic hulls can be taken to the point where no paint is left anywhere (back to 'good conditions' gelcoat), seriously osmotic hulls are 'peeled' - the gel coat removed entirely by a special mechanical plane-type tool. The hull is then sealed with the barrier and paint applied to that (after proper prep)

Boats without osmosis issues are often barrier coated as a precautionary measure. If you have NO osmosis whatsoever on a 40 yr old hull it's possible that it's actually already been barrier coated, if not you're not likely to have that problem.

In your case, fill and fair the deeper gouges, removing all the old layers of paint would be a good idea. After that, it's kind of your option.. simply repaint, or barrier coat for peace of mind. Time will tell which decision was the right one....

davidpm 03-24-2013 10:45 PM

Re: bottom
Gelcoat will no do you any good at all. It is not a barrior to water.
I have spoken to many many people who have ground their hull.
Not one has ever indicated they would do it again.
Some kind of blasting, usually soda blasting or sand blasting depending how deep you need to go is the way to go.

Arjen 03-24-2013 11:23 PM

Re: bottom
Thanx, so no gelcoat under the waterline. And best not to start grinding non-damaged areas.

Barriercoat is normally only used under water right ?

I also want to redo the above water parts, (topsides, deck, cockpit) either with paint or with gelcoat. Above water, there is damage, but its rather minimal, a few tiny scratches that i will fill. Now i was thinking the gelcoat is both cheaper (30$ vs 100$ a galon) and stronger than paint and intended to apply that. Am i right or is gelcoat not a good idea ? I should have a spray gun available for either. I will also be including some antiskid in it. I am not yet entirely sure what that is gonna be. If i find a good product available for a reasonable price ill buy it, else i intent to use the finest sand i can find.

TQA 03-25-2013 10:02 AM

Re: bottom
Re fixing your bottom there is a really good guide here CLICKY

I would be VERY cautious about spraying polyester or vinylester gelcoat onto either topsides or decks as a refinish method. It has a VERY poor reputation as far as adhesion is concerned. Basically it does not bond to cured fibreglass. I have seen such a job where the applied gelcoat was coming off in sheets JUST weeks after the job was done [ and paid for ]

downeast450 03-25-2013 02:02 PM

Re: bottom

Drying the exposed laminate can be helped dramatically by careful "washing" the spots/scratches/gouges with acetone. Acetone is very volatile and evaporates quickly. It is also very flammable so no smoking!:D. It is a great solvent because it will dissolve both oil and water the way alcohol does only better. If you have exposed laminate you suspect contains moisture, saturating it with acetone and letting the acetone dry (you can warm the surface with an electric heat gun or lamp if you are careful) will dissolve water and take it with it when it evaporates. It helps a lot. It is such a good solvent for fats and oils it will remove them from your skin, too if you let it wet your hands for prolonged periods. It also has the insidious ability to take molecules, that would other wise be too big, through semipermeable membranes (like skin). I use it a lot and have for decades. Chemists use it as a rinse for lab ware that needs to be dry and "chemically clean" (a high standard).

Put on some eye protection and some nitrile gloves, wet a clean rag with it and "sponge" the spots with the rag. Keep the rag wet with acetone. Get your target laminate saturated with it. You can tape a rag to a bad spot and keep it wet. It will "draw" the moisture out. It will also dissolve other stuff. Some plastics will dissolve in it. Your watch "crystal". :o Just keep it off anything you don't plan to remove. Some paints will soften, too.

I have a couple of gallons in my shop beside the alcohol, the xylene and the white kerosene. They are all dangerous chemicals but no more dangerous than gasoline so treat it with the same respect.

Good luck,


Faster 03-25-2013 02:28 PM

Re: bottom
Antifouling paints should not be sprayed... very toxic and the solvents used are probably worse.

Topsides and decks are best painted with two part polyurethanes, nonskid applied with the various purpose-intended coatings like Kiwigrip will yield best results. Adding sand is an iffy proposition.. eventually the paint wears away and the dark sand is exposed.. rather unsightly after a while...

jameswilson29 03-25-2013 02:39 PM

Re: bottom
You might consider using a paint scraper to remove any peeling paint or chips, sand down bottom to a relatively even surface, apply bottom paint with roller and brush, and go sail your boat.

See how it looks next season. By then, you will have even less passion for a bottom job and will probably just do the same thing. Works for me!

Arjen 03-25-2013 08:02 PM

Re: bottom
Thank you all, This really helps :)

When i sand down my bottom to an even surface, is it no problem if there will still be some of the old antifouling remaining and i paint the barriercoat over that ? or should i maybe only apply new barriercoat to those areas that are exposed and/or going to be repaired and not where the old antifauling is still firmly enough attached to the hull that a bit of paint scraping and some sanding will remove it ?

Faster 03-25-2013 08:14 PM

Re: bottom
The barrier coat is intended o be a continuous membrane, so a patchwork approach probably won't fly unless you're repairing damaged parts of a previous barrier. In any event the barrier should not be applied over old anti fouling, I'm afraid.

If the bottom is blister free and it's just a matter of some spot fairing and sanding, then simply cleaning, painting as jw29 suggested may be all you need for now, and go sailing.

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