MacGregorSailors.com

Looks like alot of armchair amatuer chemical engineering going on here, it sounds like the sky is falling to me.

Is the ballast tank fg? Just curious I never thought about it.

Ixneigh wrote:I intend to turn the water ballast area into storage for potable water and supplies.

In the tank it's not possibly to barrier coat. What if I made the ballast water acidic by pouring in a few gallons of vinigar? Would that preclude ever having blisters if I decided not to butcher the resale value of my boat by modifying the ballast tank?

Thanks.
Ixneigh

Ix, you don't need to worry about blisters in the tank. It won't happen. However, you shouldn't use the tank for freshwater as it needs to remain full to be safely effective. A half-full tank is more destabilizing than an empty tank because moving ballast is not predictable. The factory warns against operating with a less than full tank.

Back to blistering:

There are two entirely different types of blistering. They're both very different, and they shouldn't be confused. The first type is gelcoat pimple blisters, which are merely cosmetic in nature, and the second type is fiberglass delamination, which is "cancerous" and should be repaired. Speaking about "blistering" as a general term is very confusing and can lead to a lot of unnecessary repair, or the ignoring of very necessary repair.

Type 1: Fiberglass blistering
====================
The tank is fiberglass, and it doesn't blister in the same way that Gelcoat does. Fiberglass blisters are very large (like the size of a nickel) and are caused by an entirely different chemical mechanism than gelcoat blisters which are generally tiny and numerous, like small pimples.

Fiberglass blistering is caused by water being wicked up exposed surface glass fibers deep into the fiberglass resin. Water literally wicks up along the glass fibers from the surface into the fiberglass resin.

Some components of resin are water soluble, which means that they react with water to create different compounds. Some of those compounds are acids, which will eventually eat the fiberglass away. The first thing is causes is de-lamination as the acidic water builds up inside the resin.

Fiberglass blisters can form at points where glass fibers protrude through the resin to the outside, and they are almost completely exclusive to boats manufactured using CSM (chopped stranded mat, with chopper guns) vs. woven roving mats. They CAN occur at woven roving seams, but the number of open glass strands in roving which protrude through the resin is many many orders of magnitude lower than with CSM boats so the odds of this occurring are correspondingly lower.

FG blisters are the "ice-cream mush" blister problem people are speaking of, and they will eventually destroy a hull if they are not repaired. Fortunately, if caught early these blisters can simply be drilled out, fiberglass repaired, and good as new (typically better because the glass used for repair is woven roving, not CSM).

Macs use woven roving exclusively and always have. There's very little chance of having a true fiberglass blister anywhere on a Mac.

FG blisters are the cause of all the "Fear, uncertainty, and doubt" as well as all of the true horror stories with blistering. Well, those that aren't caused by unnecessary gel-coat repairs anyway.

Type II: Gel-coat blistering
===================
Both Gel-coat and Fiberglass are made out of Volitile Organic Compounds (VOCs). They're a class of chemicals that include all esters and vinyls, and they emit gaseous vapors as they cure. Curing means that the liquid resin actually turn into different chemicals over time, which is one of the reasons that they harden (they also cross-link on a molecular level as they cure).

The VOC emissions are the chemical "left-overs" after the desired curing has taken place, and they are the thing California regulates which prevents the factory from building more than one boat per day).

VOCs are the cause of new car smell and of "new boat smell". The rate of cure increases (and VOC vapor emission decreases) logarithmically with cure time, such that by about one year old, 99% of all the VOC vapors due to cure have escaped. Your car (or boat) will no longer smell new after this point. In cold climates, curing may take longer, up to two years, and in very hot climates a hull might be fully cured in six months.

The problem with Gelcoat blistering is that as the VOC emissions build up in the fiberglass and migrate to the surface of the FG. Uncoated interior fiberglass is no problem--the VOCs just drift off into the atmosphere and make new boat smell. This is what happens on the inside hull and inside the ballast tank.

Unfortunately, some of the VOC molecules are too large to migrate through polyester gelcoat. These molecules build up at the inside of the gelcoat surface between the fiberglass and the gelcoat, eventually separating the gelcoat slightly from the FG, and then eventually bursting an invisible microscopic pore in the gel-coat through which the VOCs escape. This microscopic pore then allows water molecules in through osmosic pressure in an exchange with the VOC molecules, and the pimple blister emerges in the gelcoat. Fresh water has a much lower osmotic pressure than salt water, so much more freshwater will enter through these microscopic pores. (as in reverse-osmosis water filters, the osmotic pressure of a saturated solvent must be overcome in order for it to move through the microscopy pore. High osmotic pressure = low movement)

The important thing to understand is that these gelcoat blisters are only deformations in the gelcoat, and that osmosis stops occurring when the VOCs have stopped forming--they are "non-cancerous" in that they will cease as soon as your FG is fully cured. Osmosis cannot not occur between a liquid and a solid (FG), it occurs between the water and the VOCs trapped inside the gelcoat.

If you keep your boat on a trailer for its first year, you will not get gelcoat blisters, period. Unfortunately that means a year of not using your boat. If you mostly trailer and put into salt water, you are extremely unlikely to get gelcoat blisters. If your boat sat on a show-room floor for six months before you bought it, you won't get gelcoat blisters. My boat has spent a total of eight weeks in salt water, and it has zero gelcoat blisters even though I drove it from the factory two weeks after it came out of the mold. It's now a year old and will never develop them.

Once the VOC emissions stop, you will not continue to get gelcoat blisters.

If you take your boat straight from the factory, plop it into fresh water, and leave it for six months, it will have gelcoat blisters all over it. This is why gelcoat blisters are especially likely to occur to popular boats that are selling well--they go straight off the factory line and to owners, without "curing" at a dealership for months before they sell. It's got nothing to do with manufacturing process and everything to do with age. Gelcoat blisters are also FAR more likely to occur in cold climates because the fiberglass cure time is much longer. If you notices, most of the people with pimple horror stories are from cold climates with freshwater lakes. It's just a sad fact of nature for them.

It surprises me that the factory doesn't warn against freshwater slipping for the boat's first year, but I suppose that would cost them some sales. This can occur with all gelcoated fiberglass boats, although its much more likely to occur with thinner applications of weaker gelcoat formulations. An epoxy barrier over the gelcoat may prevent water from ever reaching the gelcoat in the first place as Doupirate suggests but I have no experience with that. People in cold climates who intend to slip in fresh water should seriously investigate it.

Bottom line: You do not need to repair gelcoat pimples. You do need to repair Fiberglass blisters (nickel-sized protrusions under the gel-coat that you can pop with a knife and they will weep water).

Unfortunately, because of all of the FUD, most people don't know the difference between gelcoat pimples and actual fiberglass blisters, which leads to the loss of resale value that Doupirate speaks of. Likely he's entirely correct about that, and it's not a problem chemistry can solve. Your best bet is to print out this explanation and hand it to prospective buyers who seem worried about gelcoat pimples.

Anyway, that's the full chemistry of what's going on, and how you know what to worry about and what not to.

Hi All! There are a whole googolplex of factors that cause blistering in FRP. And there’s no shortage of technical literature on the topic. Been there, done that, years ago, don’t want to go there again. But here’s what I can recall.

The manufacturing, application and curing process of polyester resin are each much less than perfect, which leaves an end-product, to various degrees, and in various conditions, susceptible to degradation by various means.

The very choice of polyester is purely for reasons of economy, it was not chosen because it was well-documented as the most blister-prone choice available (which among the processes available, I believe it is) it was chosen because the desired end result is the economical production of a great sailboat that we all enjoy.

The presence of oxygen (and, effectively, where isn’t there oxygen?) inhibits the cross-linking that must happen in order for the polyester resin to fully cure and gain strength. Inadequate mixing, MEKP hardener ratio, gelcoat thickness, waxing, relative humidity, temperature and a myriad of other factors allow styrene, glycol and other components of the process to be left in pockets throughout the FRP matrix, which should ideally be a uniform homogeneous mix, but in practice, isn’t.

Osmotic pressure (to equalize a concentration gradient) drives water through both the permeable gelcoat and resin matrix to dilute these inclusions, and causes swelling and internal pressure, which, if great enough, and close enough to the surface, will lead to blistering, be it underneath gelcoat, or not. Or in a bilge, or ballast tank, although intrusion here is not as assisted by water pressure the way it is at the exterior surface, and is also much less likely to be seen.

The glass fibres are not always in intimate contact with the polyester resin, and can form pathways that assist with water intrusion and speed delamination. Seen that first hand. Many of us have.

The trapped solutions are also known to reverse the crosslinking process and break the matrix back down into its constituate components. While it’s most visible near the surface, it also happens within the thickness; the diffusion is happening across a very permeable parent material, so why wouldn’t it? The osmotic pressure exerting stress deeper within the thickness is not great enough to manifest itself as a blister because of the supporting surrounding material. It would not be unreasonable to expect that it might weaken the hull to some degree.

One key piece of information common to all the literature to keep in mind when trying to understand the process is that even perfectly cured polyester resin (where it exists) and gel-coat are quite water-permeable, and so there is likely not a significant water concentration gradient across its thickness. But this issue can be addressed by the use of a relatively impermeable epoxy/metallic coatings (ie barrier coat), for those who choose it for longer-term water immersion.

Pinholes in the gelcoat (or microcracking such as from hardener embrittlement), although they might speed it up, aren’t required for osmosis to occur. Its inherent permeability (it is a polymer, after all) is all that is needed.

Having said all that, there is also an annual, time-frame-based equilibrium, which varies from user to user, that has to be considered. That is, in a simple example, the ratio of the number of days the hull spends drying out (blister pressure decreasing), vs the number of days it spends having water diffused into it (blister pressure increasing). The wrong ratio and blistering appears. Hence the logic-based (Doupirate) practice of getting/keeping/storing the hull and ballast dry as much as possible.

I would think that, if under your current usage pattern you had minor blistering that was not increasing in size or number, the expense of repair could be postponed without serious consequence.

But not to mention the result when the temperature falls below the freezing point of the aqueous fluid in the blisters. (hint: way more psi)!

Sheesh. Sounds like horrible stuff, this polyester resin. Why would anyone build a boat out of that?

- B.

ps Thanks Mastreb for making my post look short!

Wow! I've missed this thread for a while and found lots of interesting ideas and opinions, some very useful and (of course) a few without much experience with the subject of osmosis.

In 1993, I ordered a new 12 x 36 Gipson houseboat from the factory and had a proper bottom job done before splashing it. Five years later when I took my precious back out, it was eaten up from bow to stern with blisters, both the small gelcoat pimples and the deeper fiberglass types. I was sick and studied everything I could find, both views on debatable issues and let it dry out for 6 months. Then I spent the next 6 months on my back intimate will all Interprotect epoxy products, grinding and filling, over and over until it would pass as smooth again. I did all the work myself and it still cost me about $2,000. I was dubious but when I removed the boat from the water again at 1-2 year intervals for various purposes, it remained perfect and was until I finally sold it years later. Still, I resolved to never do that nasty job again.

When I went to look at my 26X, I told the owner I would have not come to look at a blistered boat. It was already badly cratered with big bumps yet unbroken. He actually lied about that when I responded to his ad. When he took my low ball offer, I committed to doing this one more time. The great thing is that the M26X bottom is so much smaller than the Gibson.

I've learned about blisters the hard way and they are a serious problem. It helps that our boats are often tralered but mine stayed in the water. Having lived for seevral years in marinas with working boat yards, there is no comparison with the quality of paint and fiberglass work I've done on my boats ast compared with a hired hand, no matter how proficient or experienced they may be. The dirtiest work is usually done by the lowest skilled (paid) worker.

In my opinion, no educated boat owner would put a new boat in the water to leave any length of time without a complete epoxy barrier coat. Bottom paint is optional depending on location and use but mandatory in the rivers and lakes where I live.

Al in Arkansas (sold the M25 and now have a 2000 M26X)

One thought to you guys who insist on drinking the blister koolaid.....document your epoxy coat extensively!,

For resale purposes, you have to understand that your barrier coat precludes an inspection of blistering, so any prospective buyer will discount accordingly if you don't have either real good pictures or a well-reputationed marine shop doing the work and standing behind it.

I woud rather buy a boat with blisters that I can see than a perfect bottom paint on a hull I can't see....