Blistering on a new bottom?

[MattObjects]

When we bought our Rafiki 35 last summer, the boat's bottom was in good shape structurally (no delamination, evidence of impacts, or blisters) but covered in years and years worth of flaking bottom paint. So after we hauled out last fall, we set to scraping it all away.

Under the paint was a gel-coat type barrier coating that had been applied when the bottom was professionally re-done in 1990. It had some crazing but otherwise seemed to be in good shape. My wife scraped the entire bottom by hand (which took over 100 hours!) rather than paying someone to soda blast the bottom because we wanted to preserve that intact barrier coat. We sanded it, cleaned it, and in an overabundance of caution, applied a new epoxy-based barrier coat over it before applying bottom paint. We observed the recommended prep and cure time for each step of the process.

Sounds great, right? Well, when we hauled the boat out last week we discovered the entire bottom is now COVERED in tiny blisters. The blisters are easy to pierce with a pen knife and release fluid when punctured. If you scrape a blister off, the bottom paint and new epoxy barrier coat come off, leaving just the old gel-coat type barrier coat underneath. So somehow water has gotten between the old and new barrier coats.

I don't understand how this has happened (the boat was quite dry when the new barrier coat was applied) and am equally stymied about how to address (aside from scraping off the entire bottom coating again, which I really don't want to do) it or how to prevent it from recurring if we do scrape the bottom down again and start over. Any thoughts or suggestions would be welcome.

 

[Ted]

I'll take a guess here. You mentioned that the original barrier coat was crazed. I would guess that moisture is getting between the old and new barrier coats starting from the inside of your boat. If your bilge is often wet, moisture can migrate from inside to outside and that can sometimes cause blister problems. The new barrier coat could have trapped the moisture between the new and old. Previously, the old bottom paint was porous enough to allow moisture to escape when on the hard. I'm making lots of assumptions here so try to provide some more details as to how often the boat is hauled, how much time it spent on the hard, how much time did you allow the boat to dry out before you applied new barrier coat. Did you have the boat surveyed prior to your purchase? Was the hull dry when checked with a moisture meter?

 

[MattObjects]

Ted, we had the boat hauled out to be surveyed prior to purchase and the surveyor's moisture meter said it was dry when he checked from the inside of the boat (he said there was no point checking from the outside as the boat had just come out of the water for the survey). The boat was out of the water for 6 months before we applied the new barrier coat. When we are in the water there is usually a bit of water in the bilge below what the bilge pump can get but the blisters currently on the boat are from bow to stern from the waterline on down, not concentrated around the bilge area at all.

The hull on this boat is Airex cored, so water in the coring was my first concern with this. But the hull doesn't sound like it has wet coring when tapped with a hammer and the core inspection ports on the inside of the boat reveal the core (at those locations at least) to be dry.

 

[Gunni]

How many applications of barrier coat did you apply? What barrier coat?

 

[ITMaster]

What time of year did you do the application of the barrier and final coats? What was the outside temperature and relative humidity? Could it have been in August with 90 plus degree temps and 95% RH?

 

[KD3PC]

it really sounds as if your "original" barrier coat is not compatible with the more recently applied barrier coat. It may also be that sanding the original barrier, should have been roughing up or chemical wipe in prep for the new barrier coat.

by popping and scraping you have proven a very poor bond between the new barrier and paint and the original barrier. That is actually a good thing, as those blisters are purely related to the bottom paint and the latest barrier coat. Nothing appears to be affecting the hull, itself.

BUT I would seek out the best bottom guy in your area to have a look and confirm/advise. It sounds like your original barrier coat is doing exactly what it was designed to do. Mechanical bond and chemical bond of two barrier coats - especially 20+ years apart is very tough to accomplish.

 

[Scott T-Bird]

Your wife did 100 hours of sanding to preserve the old barrier and then you applied new barrier over it? I hate to be indelicate, but isn't that way to much effort to try to save a few bucks to avoid the soda blasting? I hope it was her idea. I know my princess bride wouldn't go anywhere near that kind of project. I understand your desire to preserve the old barrier, but if you really didn't know what it was, why would you go to that effort? Wouldn't it have been much simpler to barrier the original gel coat? You might have discovered that you had something like I discovered last fall after sand blasting.

I'm guessing that you may have wasted far more money on the new paint (not to mention the effort) than you could possibly have saved on the soda blasting. I'm not being critical or mean ... believe me, I've had those lessons served up to me on a platter on more than one occasion. I really do hope I'm wrong about my thoughts for your sake. Let us know what you find out. And, of course, hind sight is 20/20.

 

[centerline]

now that the sanding has been done, its a moot point, but I have to agree with Scott T-Bird.... in my opinion, soda blasting would have been the way to go to insure it ALL got cleaned and there were no crevices or low spots that got missed.
this would give the best chance of adhesion of the new barrier coat that you put over the top of the previous barrier coat... its no secret that epoxy doesnt like to stick to epoxy as well as one might think it should, and even the slightest unsanded dimples or debris left behind will prevent any adhesion at all in those spots, leaving a void behind it..
what type of barrier coat did the PO use on it, and what type of barrier coat did you use over it? you said epoxy, but was it formulated specifically as a barrier coat, or did you just mix up some epoxy and paint it on?.... and how long did it cure for before placing in the water, and what was the lowest temperature during the cure process?

epoxy doesnt cure in a week, and in near perfect conditions, 6 weeks is about right.
depending on what stage of cure the epoxy is in, it can be water soluable/permeable, and if this happens, it may not ever cure completely like it is intended to, and can remain permeable.
and if it was Mixed incorrectly, It will never cure...

also, any lack of adhesion in a coating will eventually cause a problem, unless its always kept completely dry, undisturbed and stress free. but a perfect adhesion to the base layer will make it all like one layer... so then it will be the adhesion of base material to whatever its adhered to underneath it, that will be the weak link.

the way I read the problem you describe, it sounds as if it is the coating you put on is the failed one.... so is it actually your barrier coat or just the bottom paint that blistered, as I have seen poorly adhered bottom paint blister also....

 

[Solarfry]

Poor application of the second blister prevention coat or the paint itself had exceeded it's shelf life. Happens to paints at a lot of stores. Sometime even the gelcoat repair is too old to work.

 

[MattObjects]

For the barrier coat, we used US Composites epoxy with West Systems barrier coat additive. We also added a coloring agent made specifically for epoxy to make it possible to distinguish the new barrier coat (green) from the underlying gel coat barrier coat (white). The new barrier coat and bottom paint were applied in March and April of this year, in coastal Maryland, on clear, sunny days. We applied 3 coats of barrier coat.

The decision to scrape by hand rather than soda blasting was not to save money, it was because we have seen boats after being soda blasted that were taken all the way down to the fiberglass mat. We knew we had pretty good barrier coat in place that had been professionally applied and did not want to remove it unnecessarily. The purpose of the project was not to replace the barrier coat, it was just to get off all of the layers and layers of flaking paint.

But I figured after all of the bottom paint was off that it made sense to apply a new barrier coat while the bottom paint was off-- kind of a belt and suspenders kind of approach. It seems now that my approach has backfired.

 

[Gunni]

So with an older boat you have NO margin of error regarding barrier coating to prevent blisters. You have to keep a robust barrier coat on the hull because your laminate is not otherwise protected by an epoxy or vinylester layer. It is one thing to sand the bottom paint off, and yet another to scrape it. Once you started to scrape away at the existing barrier coat you compromised the entire barrier system. Your protection vanished. You created the source of your blistering.

It appears that you are getting bum advice regarding your hull maintenance. Using cheap off-the shelf epoxy and mixing in some additive from West System is not they way to go, as you have learned. It saved you nothing, and cost you tons of labor - the real cost of hull maintenance. Utterly unlikely that 3 coats of "barrier coat" got the film build that was required to protect your hull laminate from moisture. And where ever the scraper or sander took off what water barrier you had, and even opened the laminate, the problem was expanded.

You will now need to start over with blister repair and barrier coating. My recommendation would be to turn the job over to a professional and be prepared to pay to have the job done right. It isn't rocket science but it needs to be done right, with the right materials.

 

[MattObjects]

I'll take a guess here. You mentioned that the original barrier coat was crazed. I would guess that moisture is getting between the old and new barrier coats starting from the inside of your boat.

It turns out that this is the answer to the puzzle. The hull of our boat is cored with Airex foam. Creating an inspection port from inside the boat to examine the condition of the coring, we found it to be damp, though we have found no delamination. It seems that while the old barrier coat was somewhat porous (probably the reason water got in the coring in the first place), the new barrier coat we applied was not porous. Which is why water blisters formed between the old barrier coat and the new. Obviously this is a serious problem but now that I know what is wrong, I can set about fixing it.

 

[Scott T-Bird]

So, if you had soda blasted and applied new barrier directly to the gel coat, you may have had the blistering between the gelcoat and the barrier anyway, I suppose. How do you go about drying the core? I'm going to be very curious about the condition of my bottom after it is pulled out for the winter in a few weeks.

 

[agprice22]

http://www.yachtsurvey.com/HiTech.htm

Well, here is an interesting article on foam cored fiberglass hulls. It is not complimentary. It is eye opening.

 

[Ted]

http://www.yachtsurvey.com/HiTech.htm

Well, here is an interesting article on foam cored fiberglass hulls. It is not complimentary. It is eye opening.

I'm surprised that the author of that article didn't mention how some solid fiberglass boats are being built with inferior products and methods. Take for instance chopped strand mat which is probably one of the weakest, heaviest methods of fiberglass construction. Lots of inexpensive solid fiberglass production boats were built with chopper guns. Just spraying the mould with glass strands with very little control of the thickness and resin content. I do have to agree with him that in most instances you pretty much get what you pay for.

 

[agprice22]

I would guess by this article, that you are gonna have a tough time getting rid of your problem once you have a damp core

I'm surprised that the author of that article didn't mention how some solid fiberglass boats are being built with inferior products and methods. Take for instance chopped strand mat which is probably one of the weakest, heaviest methods of fiberglass construction. Lots of inexpensive solid fiberglass production boats were built with chopper guns. Just spraying the mould with glass strands with very little control of the thickness and resin content. I do have to agree with him that in most instances you pretty much get what you pay for.

agreed.

 

[MattObjects]

We were aware of the risks of a cored hull when we bought this boat but hoped, based on a finding of no dull sounding spots or delamination during the survey, that all would be well. We also read several articles in which Airex coring was reviewed much more favorably than coring with other materials. What finally sold us on the boat despite the cored hull was that in our fiberglass-Airex-fiberglass sandwich of a cored hull, the external fiberglass layer alone is considerably beefier than the entire hull thickness of many other boats this size. In other words, the coring adds extra rigidity but is not critical for the structural integrity of the boat.

Fixing this will definitely be a huge pain in the ___. The plan for now is to connect a vacuum pump system to access holes cut from the interior of the boat to suck all of the moisture out over the course of several weeks. Then re-do the barrier coat on the bottom and then seal up the access holes (using removable bronze deck plates) to prevent moisture from getting back in there but maintaining a way to access the core to re-inspect as needed. If anyone on here has undertaken this type of work and has any advice to share, I'd love to hear it.

 

[Jackdaw]

If you really have damp core, you have to pull the skin off and replace the core. No two ways around it. Interesting you say its airex, which is closed cell. Where is the water?? Also are you SURE the boat has a cored hull, and cored below the waterline? Seems strange in a 16000lbs 35 foot blue water cruiser.

Note - Most cored hull production sailboats only had issues if the core got wet. Normally through thru-hull penetrations. Delamination (core separating from skins) was known in high-end, low volume race boats. The vast majority or cored hull production boats never saw this problem. Note that the paper referenced earlier was all about powerboats, and not sailboats.

 

[KD3PC]

you might spend a few bucks on one of the non-destructive evaluation (IR/laser/etc) of the hull to locate wet spots, else as Jackdaw indicates, you will need to pull the skin - everywhere it is wet..there is little chance of "vacuuming the water" out...it just doesn't work that way.

 

[Gunni]

Airex is closed cell, it cannot be vacuum extracted like a balsa core. And you will need to inspect and fix all through hull penetrations and every screw hole below the waterline. So in many ways this is a very difficult fix. It may not be worth the valuation of the boat.