I hauled my boat for painting this year and discovered Blisters, Oh Dear!
From all I have read, I’m frightened to death.
Will my boat dissolve and breathe its last breath’?
Should I grind it or blast it or peel it like a pear.
And what should I smear on my bottom so bare.
These questions are daunting and I haven’t a clue.
Pray tell what’s the truth and what should I do!
I’m not really going to add any more verbiage on the volumes of blister theories, but I want to throw out some thoughts, solid information and advice on the subject. I wanted this opinion to be brief but it ended up a bit long so most aspects of the subject would get covered. If you continue messing about in boats, the odds are that you too will end up with some form of blistering on your boat or a future boat. Practical Sailor did a survey in 1990 and suggested that one in four boats can be expected to blister in its lifetime. This to me is a very conservative estimate. Approximately 75 % of the used vessels in the 10 – 15 year old bracket I inspect have blistering to some degree. The good news is that not one of these vessels have been turned down by an underwriter for insurance purposes. About 90% of the vessels we survey for pre-purchase purposes are not rejected due to blisters on the underbody. I have only looked at two vessels in the previous nineteen years of surveying that I told the prospective buyer had serious enough delamination problems to warrant invasive testing to ascertain and verify structural integrity before purchasing. Both vessel’s had severe blistering that had led to gross delamination affecting the structural integrity of the hull.
The non-scientific country boy reason for blisters is poor quality materials and poor quality control. This fact coupled with the given that all glass reinforced plastic hulls will absorb water and the chop strand or mat used on the outside of the hull to prevent print through of the heavier laminates are the hardest materials to wet out during the laminating process. Once water penetrates the gel coat these unsaturated fibers act like wicks that speed the hydrolysis process. Some boat builders have been in the practice using the cheapest resins available to be more competitive or acid to profitability. The companies who manufactured the cheap resins are the companies that now make expensive resins to cure the problem of the cheap resins. Wrap your mind around that one. The Gougeon Brothers has a fifty two paged manual available titled Gelcoat Blisters, Diagnosis, Repair and Prevention that provides a general understanding of the most recent developments in blister repair technology. Do not contract a repair without some personal knowledge from reading materials such as these.
It doesn’t surprise me that all of this is economically driven and it doesn’t surprise me when an underbody is hauled clear of the water exposing these nasty nemeses. What does surprise me is the industry that has sprung up to alleviate your blistering woes and how the problem is addressed. When you peel off the gel coat exposing the first laminate on a vessel that is blistered, you will usually discover lots of dry unsaturated mat or chop strand. This laminate degradation is caused by hydrolysis, “split by water.” Any hydrolyzed laminate left on the boat after grind, blast or peel will eventually lead to a repair failure regardless of the coating system used. I go to lots of boat yards that have blister repairs in progress and in most cases in plain sight for everyone to see is hydrolyzed laminate waiting to dry enough to have multiple layers of’ expensive barrier coats applied. Putting good stuff over bad stuff is a band aid approach at best and an expensive one at that. No one will give any sort of long term warranty or if they do you’ll think your hull has been gold plated when you receive your repair invoice. So when, why and how should I consider a blister repair.
If your boat experiences random blisters and it is an older vessel, just deal with them on an annual individual basis. Why strip the entire underbody and run the risk of making a bad situation worse. If you have the full blown boat pox, do a spot investigation by grinding or peeling off a 1″ X 1″ gel coat patch and inspecting the outer laminate to see if the laminates is hydrolyzed. If the outer skin coats of mat or chop strand have only been affected you have no real structural loss, you may have a minor speed loss depending on design and blister size, but your boat isn’t immanently terminal. If on the other hand the blisters are becoming quite large starting to affect the laminate below the outer skin you may elect to peel the boat. Peeling is now the preferred method for several reasons. First being it eliminates costly fairing procedures associated with blasting or grinding which exposes the fibers and produces craters that may make the situation far worse than it was to begin with. Secondly, it’s more controlled and thirdly there is no blast contaminate on the hull that can be another cause of a repair to fail. If you do peel your boat, you must peel all the opaque hydrolyzed material off or it will probably blister again. If the laminate remains opaque after several cuts, you have no other option, but dry thoroughly as per the coating manufacturers recommendations and take your best shot and hope for the best. In some cases this drying can take a long time and may not get to acceptable levels for over coating.
Newer boats between one to five years that develop blisters are covered under the manufacturer’s warranty in a lot of cases. Boat/US did a survey in May 1998 that contacted boat manufacturers requesting this information and quite a few were willing to share their warranty information. At any rate, it certainly is recommended to inquire as to weather or not your new hull is covered under manufacturer’s warranty. If a newer hull develops blisters it is an uncertainty as to how many future blisters will develop. My opinion is that it’s better to own an older vessel that begins to blister late in life than to own a new vessel that blisters early on.
I would like to be a voice crying in the wilderness and cast a stone at a misconception. A moisture meter is not a crystal ball device that will tell one if a hull is going to blister. I have two moisture meters and lots of older boats have high moisture contents and don’t blister and some have relatively low moisture contents and do. The moisture meter can not be used to read moisture in laminates over bottom paint or gel coat. You have to take the icing off the cake to taste the cake. I have heard of one surveyor running his meter over a hull and stepping back and exclaiming that this hull had absorbed 3,000 lbs. of water. Yes, and the moon is made of green cheese. The boat is either blistered or it isn’t. The moisture meter is a useful tool for diagnosing some problems and is a necessary tool to check moisture content of peeled hulls prior to applying costly barrier coats. It doesn’t, can’t and won’t tell you if a hull is going to blister or at what rate or time frame. I keep mine in the box most days and those who say they can prognosticate blister development are misinformed. I’ve never wasted one dollar on a fortune teller and at this late date, I’m not starting now.
Hull thickness and laminate schedules have a lot to do with how blistered boats are repaired. If you have a very light displacement thin skinned vessel, you can only peel so much or you will start to loose in the strength arena. If this is the case you may be looking at the necessity of re-lamination which can really escalate repair costs. On the other hand if you have an older medium to heavy displacement vessel you can afford to make more cuts without the risk of doing anything but getting rid of that bad hydrolyzed material. There are some boats around that have very thick mat or chop strand that can be cut down to nothing without ever getting the bad stuff off because it’s all bad. Diagnosing the extent and cause of blistering is fundamental and necessary prior to initiating a blister repair. How much of a problem do I really have are questions that need to be addressed before beginning a blister repair. Are the blisters in the skin out mat or do they go into the structural laminate. Is delamination occurring, i.e., separation between mat and inner layers. No matter what methodology is utilized to correct blisters, substrate preparation, preparation and more meticulous preparation and quality control and more quality assurance during the process is a paramount factor in preventing future failures. Something as benign as a wipe down rag can make the difference of a repair working or failing. It’s all in the details. Adequate drying by an acceptable means such as tenting and utilization of de-humidifiers or heat lamps is also paramount to a successful repair. Monitor the moisture bi- weekly and insure that the laminate reaches its lowest moisture content before over coating. Patience is a necessary ingredient. Sometimes the moisture content will plateau for a while before falling again. You can’t coat a wet hull. Again as stated earlier in this article, obtain a blister repair manual such as the one published by the Gudgeon Brothers and read and understand at least the basis before considering a repair.
There are lots of things to consider before launching forth into a blister repair job. Cost is foremost. A good blister repair job isn’t cheap. The technology is evolving as I write this opinion and who knows, maybe next year someone will come up with a really good mouse trap. My boat was blistered when I bought it and it’s still blistered. I would cross the Atlantic with all my blisters, nothing doubting. Last haul out, I painted them black and to me they look much better that color. Structurally my vessel is sound and at this stage in my life a lengthy haul out is not convenient.
If you’re looking to purchase a vessel and it has a badly failed blister repair, I would much prefer buying one that was just blistered and not repaired. Then at least I would know that no bad procedures had been performed and I wouldn’t have to be facing putting good stuff over bad stuff twice.
I am not alone with my advise to blistered boat owners. If you choose to repair, remove all the hydrolyzed chopped strand matte with a planing cutter. Sand blasting is not my preferred method because of the following reasons: #1 Without a skilled operator sand blasting can crater the bottom necessitating costly fairing; #2 Sandblasting can embed gel coat or bottom paint particles in the laminate causing possible bonding failures from contamination. Rotary grinders can cause the wash board effect that will also lead to costly fairing. Hammer sound the hull after removing all bad laminate to detect and correct and inner laminate voids or delaminations especially with cored hulls before over coating. If you spot repair blisters, do not use microballons or fairing compound of any kind. It will fail. Have the pros do the job. Use quality resins that aren’t cheap . The cheap resins started the problem in the first place. If you aren’t willing to pay the price to do it right, don’t do it. Take the money you would waste on a botched half way repair and cruise the Bahamas for a month or two. Believe me, the memories will be much better. If blisters were like sin, the repair would be free. Remember the lord loves sailors.
© Neil K. Haynes September 1998