If you are concerned about blistering, want to avoid it, need to repair it or want to design a boat so that it is minimised, Tony's book is the read you need. Less than $20 and a great addition to your yachting library. (You can find it here on Amazon for only $13.57!).
tidalwave wrote: ... Does painting the bottom stop any further damage...or will I have permanently damaged the hull?
The defective fiberglass & resin (*) become water infused by the seepage and pressure. Standard procedure for repairing blisters is to open all damaged areas (sandpaper) and dry out the hull, later filling gaps and covering all with epoxy paint. The drying process can require months, or tenting with a heat source. Filling and fairing the hull is time consuming and costly, and you've lost the original smooth gel-shine and consistent hull color.
Appropriate coating with same epoxy paint would have prevented the problem in the first place. Even if only 20% of Mac hulls might have the inate manufacturing defects to create blisters ... I'd rather epoxy the hull than run that risk. Each owner chooses his own risks. If I expected to remain afloat for more than 30 days, I'd paint the hull.
(*) The higher quality boats now use vinylester resin for the outer hull layers, and even offer long-term warranties because it has proven more resistant to osmosis. However, "defective" is still a matter for interpretation. Macgregor Yachts specifically excludes blistering from any hull warranty.
The blisters are caused by the water reacting to the chemicals in the fiberglass, causing an acidic reaction and resulting gas buildup. The fiberglass is damaged not just where the blister is, but also for an area surrounding the blister. It is important to remove all of the damaged area and then replace it with a strong epoxy-based filler. There is *much* more to it than I can write here, so I strongly recommend that you try and get a copy of Tony's book on the subject (see above) as it goes into great detail on the repair process. As far as I know, it is the only book that is specifically directed to this issue, and he does a very good job of going through the causes and repair process (so long as you can get used to the British way of calling it 'glassfibre' instead of 'fiberglass'! )
I really can't be that complicated to require and entire book. I have West Systems epoxy, flox, gelcoat, Dremel tool, heat gun and should be able to figure it out.
I think you simply grind out each blister, let the boat dry out in a warm barn for a few months, then epoxy and fair all the repairs. Epoxy barrier boat the bottom and then bottom paint. If you have hundreds of blisters, this is a lot of work, plus not everyone has a warm dry barn and a few months to wait.
If ALL the water is not removed, the repair probably will not hold.
I was not aware that water "reacts" with fiberglass. Just thought this was an osmotic pressure mechanism. What is the chemical reaction formula?
Just trying to learn if I oversimplified it.
I'd heard enough stories that we just decided to get a barrier coat and bottom paint. I cost about $1400. I had intended bottom paint anyway but decided to not take a chance on our new boat so got both. I've always wondered about osmosis causing blisters on the inside of the ballast tank. Maybe it's no big deal since there's no gel coat to damage.
On Lake Angostura in SD before we bottom painted our Mac 25 we had quite a cleanup to do in the fall after pulling the boat. Muriatic acid is what we used to clean the hull; nasty stuff but it really took off the algae and didn't seem to damage the gel coat. Make sure you wear a charcoal filtered mask if you use it. I prefer having the bottom paint by far.
I think I am only going to fix the ones where the gelcoat popped off and other are cracked then wax and use the boat this summer. It will rarely remain in the water for more than a couple of days with a week or more time out of the water.
It really needs to dry out for a long period of time.
I guess I have "pimples". They are conspicuously along both spare lines.
WHAT IS OSMOSIS?
Osmosis is a process of degeneration within a fiberglass laminate. It is caused by a chemical reaction between water and unreacted substances remaining in the manufactured hull. The water enters the hull through the gelcoat and once inside, reacts with the chemical components creating acidic substances. These substances create pressure behind the gelcoat, which causes blisters and eventually cracking. Once the gelcoat is breached in this manner, the underlying laminate is capable of absorbing water like a sponge. Osmosis is not only caused by water on the outside of the hull bilge water from the inside can also cause a problem. It is therefore worth making efforts to keep your bilges dry.
WHEN MIGHT OSMOSIS OCCUR?
Any unprotected hull is likely to show signs of osmosis eventually, like rust on a car. The exact length of time before osmosis occurs depends on many factors including: the type of water in which the hull is moored; the temperature of the water and most importantly, the quality of the original hull construction. In some cases, reactive impurities in the gelcoat and laminate will cause osmosis in the early life of the boat. This is a structural problem and should be referred back to the boat manufacturer. However, even well-built, fiberglass hulls will eventually experience osmosis and blistering. This is why we recommend applying an epoxy protection layer, even to new boats.
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