Under Bottom Paint

Len · Post by **Len** » Mar 27th, '10, 15:03

Minke is starting to show her age (11) and the condition of her bottom is nearing the point where I can forsee having to strip her bottom in a year or two. In the meantime I was wondering if there is any recommendations for what, if anything, to apply to white /gel coat exposed by sanding before applying new bottom paint. The blotches are getting to big to avoid sanding the gelcoat.
Len

drb9 · Post by **drb9** » Mar 27th, '10, 20:47

Maybe this is not your problem, but maybe it will add to your description. I have a 26, and I used ablative paint. Each year, when I visit the boat to paint her bottom, I find that there are sections thick with bottom paint, and when I scrape those sections, paint chips fly off, leaving just the white bottom. I had thought that ablative paint avoided the need to scrape and remove bottom paint, but without the scraping, the big chips come off on the roller. Am I applying too much bottom paint? Is it normal for accumulated layers of bottom paint to flake off?

Kevin_P · Post by **Kevin_P** » Mar 28th, '10, 07:58

Hi,
It sounds like you'll need to sand down, then barrier coat to avoid water penetration into the fiberglass. Not a fun job... we've been there.

Regards,
Kevin

David van den Burgh · Post by **David van den Burgh** » Mar 28th, '10, 08:44

Len,

I'll just throw this out there: There are different schools of thought with regard to barrier coating. Ariel was barrier coated by a previous owner, and I think it's caused more problems than it solved; in fact, I don't think there was a problem until the barrier coating. Every year upon haulout, there are tiny blisters of water trapped between the gel coat and the barrier coat. Either the barrier coat is too thin (probably an easy mistake since the stuff is so expensive) or the hull was not properly dried before application of barrier coat.

Anyway, before going to the trouble and expense of barrier coating- if that's even a consideration - I'd clean up the bottom with a scraper and a bit of sanding, reapply bottom paint, and see how she does for a season or so. If haul out reveals a blister problem, address it. What I've read and heard suggests that you're probably not going to have a problem with blisters if you haven't had one yet.

Best of luck.

Steve Laume · Post by **Steve Laume** » Mar 28th, '10, 09:23

David is precisely right!

I have taken two Cape Dorys down to gel coat now. The first was my Typhoon and I debated adding a barrier coat. Time and money dictated that she go without. I sailed her for four years with absolutely no problems, with the hull and bottom paint.

I also hand scraped and sanded Raven down to gel coat, her first year under my ownership. She had one blister under the boot stripe but no other problems. Wanting to do things right, I debated and then finally decided to add a barrier coat. I did not use a moisture meter to determine her dryness but did build the recommended number of coats. The next time I pulled her out and every time since I am getting the tiny little blisters under the barrier coat.

To treat these blisters I sand through them and feather back to the gel coat. I suspect that I will eventually remove all of the expensive and time consuming barrier coat that I once applied. None of the areas of bare gel coat have caused any problems.

It seems that the marine industry is always trying to sell us something. For some boats a properly applied barrier coat might be beneficial. As for the vast majority of Cape Dorys, I would say if it ain't broke don't fix it.

I never imagined the the prevention I thought I was providing would become the problem. Steve.

drb9 · Post by **drb9** » Mar 28th, '10, 09:45

The previous owners of my boat paid to have a professional apply a barrier coat, after addressing blisters in the gel coat. That was 12 years ago (long past the 5 year warranty provided by the contractor). So far, I have had no problems.

(I had some wierd area at the bottom of the rudder--it looked like some of the gel coat came off-- but I can't tell whether that was caused by the barrier coat or had more to do with the rudder attachment.)

Neil Gordon · Post by **Neil Gordon** » Mar 28th, '10, 12:35

I'm thinking it's an adhesion problem and not water penetrating the gel coat. Multiple layers of paint, multiple years of temperature extremes from winter to summer, freezing and thawing on the hard, half the year soaking in water, half not, etc., etc. We're lucky any paint stays on.

I've had fair sized patches of bottom paint come loose. I've given the bare spots multiple layers of new paint which has held just fine, as each season some new areas of older paint flake off.

drb9 · Post by **drb9** » Mar 28th, '10, 14:23

Neil, that sounds like what happens to me. I'm not terribly concerned by it, because the point of bottom paint is not to protect, for example, raw wood underneath, but to keep barnacles away. I'm just confused, because I thought the point of ablative paint is that it is supposed to slough off gradually, not build up many layers that eventually chip off in chunks. I can't imagine that it helps my speed to have splotchy bottom.

Darin

Neil Gordon · Post by **Neil Gordon** » Mar 28th, '10, 14:34

drb9 wrote:I'm just confused, because I thought the point of ablative paint is that it is supposed to slough off gradually, not build up many layers that eventually chip off in chunks. I can't imagine that it helps my speed to have splotchy bottom.

That is the point. I suspect though, that many of us put more paint on the bottom than is needed, season after season and also whether there's just so much adhesion that can stand up to multiple seasons of soaking, freezing, thawing, soaking, etc.

And yes, speed is better with a smooth bottom. I can't bring myself to sand off all that good (and expensive!) protection, though.

mgphl52 · Post by **mgphl52** » Mar 28th, '10, 14:39

A light sanding to rough up whats left and "smooth" the gaps may help. However, I've always used hard bottom paint and only repaint every two to four years. We also don't get frozen water (often...) down here.

After many repaintings with soft paint, I really think it would be a good idea carefully clean, sand and reapply with a "fresh" bottom.

-michael

Mike Thompson · Post by **Mike Thompson** » Mar 28th, '10, 19:46

I'm in Maine where the water is cold and mostly clear. I keep the boat (CD28) on a
mooring. The bottom has never been totally redone down to the gelcoat. In some places
the paint is thick. After every season the paint comes completely off in
small patches here and there however I think this is due to very old paint
and the gelcoat is fine.
First I scrape the whole bottom very quickly just to remove loose paint. Then I
put one coat of 100% paint on the white patches, inside the through hulls and also just below the boot stripe. Next I thin the paint to 75% for painting the hull starting
at the top. Further down I thin to say 50% for the keel. I use regular paint thinner.
The further from the surface the less marine growth occurs. This method
helps avoid paint build up.
Mike

Steve Laume · Post by **Steve Laume** » Mar 28th, '10, 22:07

How much do you thin the paint you put on the bottom of the keel?

I go heavier near the water line too. It is there and the bottom of the keel that always seem to grow the best marine life. The stuff around the water line is easy to scrub off while swimming. It is the bottom of the keel that either doesn't get a real good coating, none at all because of blocking or is removed by some other mysterious means that is harder to deal with.

It's getting to be about that time. Steve.

Neil Gordon · Post by **Neil Gordon** » Mar 29th, '10, 06:01

Steve Laume wrote:It is the bottom of the keel that either doesn't get a real good coating, none at all because of blocking or is removed by some other mysterious means that is harder to deal with.

I'm amazed sometimes at the underside of some of the wing keels in the boatyard. Their bottoms are especially hard to paint and especially easy to forget to paint. The little critters love them!

The Patriot · Post by **The Patriot** » Mar 29th, '10, 06:43

Neil Gordon wrote:
Steve Laume wrote:It is the bottom of the keel that ... doesn't get a real good coating ... or is removed by some other mysterious means ...
I'm amazed ... at the underside of some ... wing keels ... Their bottoms are ... hard to paint and ... easy to forget ...

Department of Local Knowledge - Mid-Atlantic Region

Local custom on Barnegat Bay (NJ) is to save paint and ignore keel bottoms. The Bay is quite shallow and any paint wasted on keel bottoms is quickly removed during springtime sea trials. The same fate awaits bugs later in the season.

Maine Sail · Post by **Maine Sail** » Mar 29th, '10, 06:44

David van den Burgh wrote:Len,

I'll just throw this out there: There are different schools of thought with regard to barrier coating. Ariel was barrier coated by a previous owner, and I think it's caused more problems than it solved; in fact, I don't think there was a problem until the barrier coating. Every year upon haulout, there are tiny blisters of water trapped between the gel coat and the barrier coat. Either the barrier coat is too thin (probably an easy mistake since the stuff is so expensive) or the hull was not properly dried before application of barrier coat.

Anyway, before going to the trouble and expense of barrier coating- if that's even a consideration - I'd clean up the bottom with a scraper and a bit of sanding, reapply bottom paint, and see how she does for a season or so. If haul out reveals a blister problem, address it. What I've read and heard suggests that you're probably not going to have a problem with blisters if you haven't had one yet.

Best of luck.

Barrier coating done correctly works well, though VERY few yards do it correctly and apply barrier over a substrate that is not dry. A proper barrier coat job involves a moisture meter.

In answer to the OP you are applying WAY to much paint and/orusing a product with a high ablading speed such as the Micron line. Micron paints don't even begin to ablade until 6-7 knots. Pettit Horizons and the Ultima line begin at 2-3 knots.. Pettit SSA (single season ablative or super soft ablative) ablades even faster..

Don't do anything but scuff the bare gell/re-paint until you're ready to strip the whole thing..

The Cape Dory Board

Under Bottom Paint

Under Bottom Paint

Me, too

barrier coat

Bottom work

Hoe much paint?

Re: Bottom work