bottom problems

[RonSanga]

Has anyone experienced small holes in your gel coat? I have just removed the bottom paint and found LOTS of holes in the gel coat. It looks like a golf ball texture but a little deeper. I sanded off some of the gel coat and the fiberglass looks good. No blisters at all. Should I take off all the gel coat or fill and fair the gel coat. The marina wants to just fill it all in but I am worried that whatever caused the holes will just come back again. The bottom of the holes is light green and shiny. The sand blasting did not change the look of the green, so if it is that hard and shiny isn't that a potental problem?

thanks, Ron

[Oswego John]

Hi Ron,

I can't comment on what your problem is but I have a few questions for you. Where do you tie up or moor your boat? Salt or sweet water? Moving tidal flow or current, or in brackish, standing water.

It may or may not be related, but we almost lost our schooner because of microbiological attack on the steel hull. For years, we tied up in a small arm of standing water adjacent to the harbor. It was in sweet water without any tidal effect. It wasn't caused by rust, but by the opposite, lack of oxygen.

Unbelievably, those little buggers ate holes halfway through 3/8" well protected steel.

Good luck,
O J


ull damage.



Keel and plate damage



Fitting new steel plate.

[RonSanga]

The boat had been moored in brackish for many years but now will reside in fresh water. It almost looks like someone tried to repair it once but did a bad job and it failed. I guess I'm most concerned that the new material will not bond to what ever it is that is so shiny.

Ron

[mashenden]

I'm no expert but it sounds like a blister problem from osmosis (water getting in then forming small blisters) that then had the blister tops knocked off during sanding leaving small craters. I have seen serious blistering that resulted in holes all the way through a hull. Less severe cases could look like what you are describing. It is reported that this occurs in varying degrees of severity if there was moisture introduced when the epoxy was mixed or applied, or improper mixing of the two parts.

I think if it were mine, given the description of small divots, I would fill and fair the hull, then put a good barrier coat below the water line to protect against any further water absorption. Barrier coatings are designed to have a very tight molecular structure that keep water out.

[Sea Hunt Video]

Ron:

I preface my remarks by stating I am a rookie at all of this.

That said, it sounds like gel coat blistering. Below is a website that briefly discusses dealing with a few blisters on the hull.

http://www.boatus.com/boattech/casey/blister-repair.asp

If you have a lot of blisters, I believe Don Casey recommends removing all of the gelcoat below the waterline. Expensive and time consuming but necessary.

You may want to get Casey's book Sailboat Hull and Deck Repair. It is well worth it. He has a chapter devoted to what he calls "boat pox". In essence, a hull covered with gelcoat blisters.

[Markst95]

If its just in the gelcoat whats the harm in slapping some bottom paint on and not worrying about it?

[Duncan]

Has anyone experienced small holes in your gel coat?...

I have, on a previous boat, and I don't think you have much to worry about.
These pinholes showed up along the waterline, but they were just a surface rash in the (porous) gelcoat. They are not the sort of blisters that develop deep inside the hull laminate.



Even though this is not a serious problem, I think it would be sensible to apply a barrier coat.

[mashenden]

If its just in the gelcoat whats the harm in slapping some bottom paint on and not worrying about it?

It will probably (read: most likely) get worse. If one wanted to skip the fairing step, I would slap some barrier on (as also noted by Duncan) before the bottom paint. But that would still mean doing respectable bottom prep so as not to waste the barrier effort.

[Rnoonan]

This happened to my father's boat when we moved from Narragansett Bay (salt) to Lake Ontario (fresh). Point being, it's always been our understanding this issue is much more prevalent in sweet water due to the lower specific gravity and ease in permeating a membrane (gel coat).

I don't believe he ever removed the gel coat. Although it took several seasons of experimentation with expensive cans of paint + sanding, he eventually came up with a combo of barrier coat and ablative paint that stopped them from appearing. But I would agree with some other suggestions that the depth of the damage should be considered.

[NateHanson]

When I walnut blasted the bottom of my 1971 Columbia, hundreds of little gelcoat pits, about 1-2 mm diameter, were left where the blasting medium had hit gelcoat with a small void behind it. I squeegeed thickened epoxy into them (used a very light weight filler, so it would sand easily). Then orbital sanded the bottom to smooth out my work. Then Barrier coated over that. Looked great 8 years later.

Considering that these boats are already 30-40 years old, and have very very very minor blisters (if they even are osmotic), I think removing the gelcoat entirely would be overkill. Fill em with some epoxy. Barrier coat over them, and remember to check it again in 2045.

(I'm not suggesting that all blisters be covered up and ignored, but this type of tiny gel-coat voids only evident after blasting are not in my opinion indicative of any problem.)

Nate

[RonSanga]

There are two reasons I can't just slap on a barrier coat and call it a day. First I want my boat to be done the right way and look good, but the biggest reason is that Pyxis sits just down the dock watching over me. That's a lot of preasure.
I guess I will fair it all out then barrier coat and bottom paint her.

Thanks for all the good advice, Ron

[mashenden]

That is called Pier Pressure

[Rnoonan]

No solutions contained, but I'm reviewing the all products, 1981 owner's manual and came across this section. Just thought it was appropriate to have it attached to this thread:

GELCOAT BLISTERS: Below the water line it is possible for water to get beneath the gelcoat and cause it to blister. This occurrence is rare and usually takes the form of small blisters less than 1/4” in diameter. While we try to use the latest materials and techniques in combating this phenomenon, it is not within our ability to guarantee this never happening due to the very nature of the materials used. If you should find yourself with a serious case of the “measles”, contact the factory for the latest recommended repair practices and advice. The successful repair is difficult and time consuming and the services of an expert repair facility is advised. To minimize the potential of blisters ever forming on your bottom, this advice is offered: Never sand your bottom gelcoat off. Do not use pumice stones or a coarse sandpaper when preparing your bottom for new bottom paint. This only deeply scratches the gelcoat surface which increases the chance for water to pass into the laminate. Gelcoat is a water proof barrier coating required to protect your boat’s laminate, not merely a cosmetic coating.
The continued use of an epoxy based bottom paint is recommended.

Ty-Ty Wkndr-22D-25D-27-28-30-30K.pdf page 20

[Duncan]

GELCOAT BLISTERS: Below the water line it is possible for water to get beneath the gelcoat and cause it to blister. This occurrence is rare and usually takes the form of small blisters less than 1/4” in diameter....Do not use pumice stones or a coarse sandpaper when preparing your bottom for new bottom paint. This only deeply scratches the gelcoat surface which increases the chance for water to pass into the laminate. Gelcoat is a water proof barrier coating required to protect your boat’s laminate, not merely a cosmetic coating.

That's an interesting "find", and I think it's about half-right.
The part that's right is that sanding increases surface area, and therefore the potential for water to penetrate.
The part that isn't right is that polyester gelcoat is waterproof. It's not, or at least not forever.

As noted in the two links below, gelcoat is porous in the first place, and gets moreso with exposure to UV. It is noted that this porosity can be aggravated by overly-thick application (a known issue with Cape Dorys).

Putting this together, it's not hard to see how pinhole "blistering" can occur along the waterline. The overly-thick gelcoat is prone to porosity in the first place. Then, along the waterline, the alternating exposure to sunlight and water aggravates this porosity (by degrading the gelcoat and exposing it to water penetration at the same time).

http://www.wingsandwheels.com/Weather%2 ... 20Tech.htm
http://www.doctorgelcoat.com/2010/03/porosity.html

So, applying a fresh, epoxy barrier would appear to be a good first step. After that, protecting the epoxy from UV close to the waterline looks like the best way to keep the new barrier coat from degrading with exposure.

[mashenden]

...
The part that isn't right is that polyester gelcoat is waterproof. It's not, or at least not forever...

Agreed, nothing is waterproof, with the possible exception of the crud that accumulates over cockpit scuppers or in rain gutters. I wonder why they do not make barrier paint out of that stuff??

But seriously, I suspect CD's claim that gelcoat is a waterproof barrier was relative, in terms of what was available at that time and in comparison to the laminate. Since then it has proven to be more susceptible to penetration of moisture than initially thought, so a better barrier coating has since evolved as a result of improvements in epoxy technology. Yeay.