osmotic blistering and bottom paint questions...

[zuunami]

While we have our 16' out of the water and cleaning the hull of some barnacle "residue" (thanks to Thataway for his suggestions in an earlier post), we're wondering about ablative bottom paint. Not the up the sides kind of paint, but just on the bottom where we can't get to the hull because of the trailer bunks when we have it out of the water. The PO left it in saltwater too long (about 6 months) - but we've found the "residue" pretty easy to remove where we can get to it. And it won't be left in the water for huge amounts of time in the future.

But in reading about bottom painting, it's suggested at least two coats of epoxy (to a certain mil thickness) before bottom painting. I understand that the epoxy is intended as a less porous barrier to prevent the processes that promote osmotic blistering, but why are the coatings of epoxy only mentioned in terms of bottom painting? Why shouldn't everyone just put two coats of epoxy on the bottom of their boats? Sorry for my ignorance, just would like to understand

I've read a number of articles, this one has been most helpful in understanding the dynamics of osmotic blistering, maybe someone has better references they can refer me to?

https://stevedmarineconsulting.com/wp-content/uploads/2014/03/Blisters-and-Osmosis.pdf
thanks! - Karen

[thataway]

Osmotic blistering in C Dory boats is relatively rare. I recommend that any boat which is going to have any type of bottom paint applied have the barrier coat which prevents (not eliminates) the osmotic blistering. Two part Epoxy high solids coating allows less water to pass (semi permeable) than gel coat or polyester resin. Once you sand the bottom to apply any bottom paint, there will be scratches. These have to be removed by either sanding or media blasting before the epoxy barrier coat is applied.

If putting on bottom paint--I would bring it to the waterline--not just the bottom. Although I have spent 4 years sailing in the PNW, most of my boating is in warm waters. There is less blistering in cool waters. I can give examples of boats which have bottom paint vs boats which don't. In the Florida Keys, after one week there are some barnacles starting to grow if there is no anti fouling paint. These boats have to be taken out of the water and cleaned every week. I had Petit Vivid ablative paint, on my trailerable boat, and after 4 months there was a bit of slime, easy removed with a pressure washer.

When we had the Cal 46 in John Wayne Marina for the winters and travels in PNW to AK from May thru Oct, I had to have a diver clean the bottom about once a month (about 30 years ago) The boat had a hard bottom paint. In Florida, we had to repaint every 2 years, even with bottom cleaning.

For the C Dory 16 which is kept in the water only a short time, Petit Vivid will last a number of years.

[T.R. Bauer]

Cool temperature do make a big difference. I can leave my boat in the water for a couple of weeks and have almost nothing growing at all in PWS and Cook Inlet waters and I don't even have bottom paint.

[hardee]

Before I had bottom paint I had a 100 day trip up around the north half of Vancouver Island. I was moving almost every day, but almost always slow cruise, (3-6 knots), and some days very short distances, 2-4 miles, but I did move nearly every day. Water temps around the mid 40's.

At 48 days, I pulled the boat to clean the hull. I had green hair, about 1-2 inches depending on location. AND some of that was above the factory bottom colored gel coat. (That is when I decided to do bottom paint and to raise the water line. I had barnacle starts, up to the size of a #2 pencil eraser, and they cam off fairly easy as long as the y were still wet. (I used a piece of wooden stick, about 1/2" diameter, with the end shaved like a flat chisel.)

I have not had the chance to get back onto the water for an extended time since then to see how the Petit is working, but quite sure I don't have to worry about barnacles any more.

Harvey
SleepyC

[zuunami]

Well, we had more than barnacle starts when we got it a few months ago, but we're getting it off with hull cleaner, scrapers, etc. (and Mr. Clean magic eraser pads, they're they most effective, hope we're not really screwing up the gelcoat The PO had left it in the water in a contained marina for about four months and ran it only a few times, so the buildup was pretty heavy.

But bottom painting seems quite daunting at this point, so we'll probably put it on our "later" list. We're going to be taking it in and out of the water (cold, saltwater) every few weeks, so we should be able to keep up with it. Wish there were a super duper wax that you could put on, but for now we'll try Meguiares marine wax, have read good things about it.

Thanks everyone!

[thataway]

Unfortunately was will wear off quickly. Collnite 885 Fleet wax is the best marine wax you can purchase. However its effect on fouling is very minimal.

[hardee]

Pretty sure Bob meant the WAX will wear off, not the "was".

Well now, this is not wax but it does keep the growth off. Not sure how practical for a bottom paint replacement, but I used it on my trim tabs on my 100 days, and it was very effective.

Zinc Oxide Ointment or Desitin. *>>Baby bottom rash treatment

Worked like magic for about 8 months, and then was still not easy to get off. For me it was too much to do the whole bottom of a 22, but, depending on how soon you get tired of washing that 16 bottom, it might be a thought. Then again, a good bottom paint probably wouldn't be much different in price, look better and save you hours of elbow bending.

Harvey
SleepyC

[zuunami]

hardee, thanks - maybe I'm confused (not unusual), but whatever we eventually put on the bottom means we have to do the work to get all of the barnacle "residue" off, then at least buff it before any product? And with some product, more than just buffing

[thataway]

[hardee]

Oh No, You're not confused. Yes you will have to get all the barnacle stuff off before you put anything on, But if You don't put something on, you will have to get all that barnacle stuff off, Every Time. Maybe no barnacles in 2 weeks, but miss one time and yews they will be starting.

Harvey
SleepyC

[zuunami]

Thataway, we've pretty much decided NOT to bottom paint at this time, as once we have all the barnacle residue off, and I mean OFF, it's only going to be in the water two or so weeks at a time, then out and cleaned. We're lightly buffing all of the boat with a Meguiar's compound as it is oxidized, and it's coming out great. Then we'll wax it. I just thought that we would finish that process on the bottom if we aren't going to paint it. But, then again, in the absence of sunlight, perhaps the bottom isn't oxidized and we can just wax it (instead of removing any gelcoat via buffing)?? Appreciate your wax suggestion, will check that out tomorrow. Thanks!

[thataway]

There are a number of slightly different products which are "Meguiares marine wax," (Paste, Cleaner Wax, liquid "M5616 Marine/RV Pure Wax Carnauba Blend", the list goes on--and I have probably tried 90% of them. Meguiares wax product go on easily and are easily buffed out.

There is more work with the Collinite 885, but it lasts longer.
What machine and what product are you using to "buff" and "polish"?

You can get acceptable--and what looks good, with a minimal effort. The problem is it does not last. If you start out with the heavy duty compounding, then a lighter compounding, polish and then good quality wax, which you never allow to complete deteriorate , the entire system will keep the boat looking good, and protect the gel coat for years. If you go for a lessor job, then you end up repeating the lesser procedure many times over.

There are so many products--and systems--whcih probably can make one very confused. Generally sticking with one system or several of the well known marine products-such as by 3M is best.

For the best compounding one goes to the heavy duty machines--such as the Makita 9237CX3 7", The DEWALT 7-Inch/9-Inch (DWP849X), There is the use of either wool or foam pads--different pads for the various stages of compounding to get a good base for the wax system. The importance is a compounding machine which does not bog down as you vary the pressure. A cheap Harbor Freight or Northern Tools, is a fraction of the cost, but just does not keep the same RPM if you put pressure on it. A circular machine to start with and the final steps with a Random Orbital machine. I have found out that a good right angle battery operated drill with a 2 to 3" foam pad works for the smaller areas such as near decals, and decks, work well on the C Dorys.

Here is a video on using the rotary buffer This person has a series of videos on how to get a quality job on compounding, polishing and waxing. While in the mood for watching, check out his other videos on polishing waxing the second machine (random orbital) etc.

Also sort of the "rage" is ceramic coating. Si02 is a cheaper variant, and may not last as long. There are the cheap DIY materials, to the professional applied which can run into the hundreds of dollars for the top of the line--which lasts several years.

There are a number of systems by: 3M, McKee's 37/Nautical one, Chemical Guys, Shurhold, Presta,Smoovewax, Starbrite, (My experience is that the Meguiar's system is just not as durable, even though it may give a good look initially.) I would suggest using one system and staying with it. Wax the boat on a regular basis--if left in the water then perhaps 2 to 3 times a year. If kept under cover--then you may only have to do a good wax job every few years. The secret is to never allow the hull to begin chalking and keep wax on the entire hull.

[ssobol]

My question about gelcoat oxidation is "Is it like Al oxidation?"

In the case of Al, the surface oxidizes and this protects the underlying material. Al oxide layer is much tougher than pure Al. (For example, the AL oxide layer on Al melts at about 2X the temp of the pure Al underneath.)

So, if you have oxidized gelcoat, does the surface oxidize to a certain extent and then the oxidation stops because the oxidized layer prevents further oxidation?

Therefore, if you remove and polish the gelcoat layer, are you removing the protective layer and having to apply products to make up for the protective layer you removed?

Yes, I understand that removing and polishing off the oxidation layer results is a shiny boat/car/surface. Some people like that. But this could be a cosmetic result and not as effective in protecting the surface material as leaving it oxidized.

[thataway]

My feeling is that the gel coat is deteriorating. The wax protects the underlying surface of the gel coat. In the Al, the oxide will protect--such as in anodizing. If you let the gelcoat continue to deteriorate, it eventually will check and be completely un-restorable.

Compare a 10 year old fiberglass boat which as regular waxing vs a fiberglass boat which has no care. My Cal 46 spent its first 10 years in the Caribbean as a charter boat--where it was rarely waxed. The gel coat was shot with severe checking on the deckhouse.. We had to sand it off, then epoxy primer and Awlgrip.

[zuunami]

thataway, thanks for all of your info, as always! We're using Maguiars One step compound plus polish for the compounding portion, and it's working pretty well. Then we have Maguiar's flagship marine wax that we were going to apply. Have some Collinite 885 coming tomorrow via amazon that will be here tomorrow and will then decide which to use (Our closest marine store is 2-1/2 hours away, and about the size of a 7-11, so we have to rely on internet purchasing for product

I have to say, when compounding/polishing, and I see that green or white on the pad, I just cringe. Unless we protect that well afterward (and I'm not sure wax does that), I will have to do it again, then more white and green will come off, and I'll more than cringe for the loss of gelcoat.

ssobol, that's what I've been thinking, especially in regard to the bottom hull that doesn't look very oxidized. So we're just hand compounding that, and then a finish. But what finish?

So we're going to do a test of a number of finishes on the bottom hull, including a ceramic spray under wax, and....

some Desitin, just for Harvey