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Repairing Blisters

April 8, 2013

A few years ago, since we were spending hurricane season in Trinidad on our 34-foot Creekmore, Eurisko, we thought we would take the opportunity to haul her out and apply another coat of bottom paint. What we found when she emerged from the water on the lift at Peak's Marina, however, turned a three-day quick haul into a three-month ordeal. We had blisters.

Blisters on the bottom of a fiberglass boat can be started by a number of different problems: a poor layup of fiberglass, portions of the fiberglass left unprotected, or gelcoat absorbing water. The initial cause is often unknown since blisters can take years to form and grow big enough to catch our attention. A boat that is hauled out every season has the opportunity for the blisters to dry out, shrink, and sometimes completely disappear before the next season. But our Eurisko had been in the water continually for years. The few dime-sized blisters that had been noted on her survey now numbered in the thousands and were quarter-sized or bigger, some much bigger. We could no longer deny that we had a problem.


Marking blisters

Knowing that grinding off all the layers of bottom paint and gelcoat down to the bare fiberglass bottom was going to be a long, hot, miserable job, we decided to hire the yard to do that part of the project. Until we got a quote. I had to verify with the secretary that she was quoting me in US dollars not Trini dollars, because the amount was equivalent to what you would expect to pay in an American yard. Finally, Dave decided that for that much money he would invest in a good grinder and teach himself to use it, a decision he regretted for several days.

In a Tyvek suit, in the summer Trinidadian sun, Dave grinded Eurisko's bottom through all the bottom paint and gelcoat. Because he was not proficient with a grinder when he started, he waited until the end of the project to attempt the waterline. He double taped above the waterline, grinding the extra inch above the real waterline. This would allow him to apply the epoxy barrier coat above the water, ensuring that no part of the bottom would be left unprotected. The decision was an easy one for us since we planned to paint the hull above the waterline while we were out. If you do not intend to paint the topsides, you will have to be more careful with your grinder as you near the waterline.


Grinding down to good fiberglass

When he was grinding the bottom, Dave took particular care to dish out the blistered material. Often there were large craters left where he had to remove a lot of fiberglass to get down below the blister. Fiberglass that still needs to be removed will often be white, and when you rub your hand over it you can feel a bump where it sticks out slightly above the rest of the hull.

After he had ground out each blister, Dave washed the hull well with fresh water. Inside each blister is styrene, created when water reacts with compounds in the hull. When you first pop through a blister you can often smell the styrene. Removing all the styrene from the hull and the craters left by the blisters will help the bottom dry out more quickly. Even if you remove every visible blister, there is a very good possibility that there are more that you did not see. The fresh water and time on land will help dry out even those blisters that you missed.


Letting the blisters dry

After the bottom was ground down, the blisters dished out, and the hull washed, we began the hardest part of the project: waiting. At $17 a day to stay in the yard, and the quarter-mile walk to the heads, it was an extremely difficult wait for us and our three young boys. The kids made friends in the boatyard, we completed various other boat projects, and we used this time to do some sightseeing. Since the longer we waited the drier the boat would be (and the less likely the blisters would return), we managed to tolerate living on the hard for three months.

One of the boat projects we completed while we waited was prepping the topsides for paint. We planned to Awl-grip the hull, but we could not apply the paint until we applied the barrier coat of epoxy since we wanted to overlap the epoxy and the topside paint.


Barrier coating

We had calculated that we would need about four gallons of epoxy to complete the project. At the chandlery we found five gallons of West Systems epoxy for the same price as four one-gallon sets. (We ended up using almost the entire five gallons.) The day we decided to begin the project there were many preparations we had not anticipate. Because of our delays, Dave only had time to apply one coat of neat (unthickened) epoxy before the sun set. The next morning he had to wipe off the amines that are created when epoxy cures and scuff the epoxy before he could fair in the craters left by grinding out the blisters. On the other side of the boat, Dave had time for his preferred method: apply the wet-out coat of epoxy and while it is still green (before it cures completely), apply the thickened epoxy to fair the hull. This method creates a chemical bond rather than just a mechanical bond, but the timing is not always perfect to allow for it. One hint about epoxying the entire hull: when you are moving the jackstands to apply the epoxy under them, be sure to cover them with wax paper to keep them from sticking to the wet epoxy.


Fairing the blistered areas

For the fairing compound, Dave started by mixing neat epoxy. To this mixture he added enough colloidal silica to partially thicken the epoxy. Colloidal silica is very hard, adding strength to the fairing compound. Once the colloidal silica was completely mixed, he gradually added phenolic microballoons, stirring until the mixture was the consistency of peanut butter. The microballoons add bulk to the compound, are fairly non-absorbant, and increase the sandability of the fairing mixture. (West System filler 410 is not recommending in this instance. It is best for less structural applications. West Systems also does not recommend 410 be used under dark paint, like most bottom paints.)

After fairing each blister hole, which was most of the bottom, we waited overnight for the fairing compound to cure, and then sanded the hull. Dave repeated the fair, wait, sand, fair, wait, sand pattern until he was relatively happy with the look and feel of the hull.


Half-way done

A waterproof barrier coat of neat epoxy is the most important element of repairing blisters. Since four to six coats is recommended, and if you can apply each coat while the previous one is still green you can avoid sanding, we decided to apply as many coats as we could in one day. With me mixing epoxy and Dave rolling it on the hull, we were able to apply five coats in one day. Dave made a small roller cover with a stick handle to "flatten" each coat of rolled epoxy after he had applied it with a larger roller.

We had double taped above the waterline with one inch tape and removed the bottom tape. This allowed us to apply the barrier coat above the waterline. Since we were painting the topsides, after the epoxy had cured we triple taped below the existing tape so that we had a line one inch below the waterline. We rolled and tipped the Awl-grip down to this line, meaning we had an overlap of epoxy and topside paint. After the Awl-grip cured, we double taped above the tape that was there, giving us a true waterline to apply bottom paint to. For one inch we have epoxy, Awl-grip, and bottom paint all overlapping.


Top side paint done

Before applying the bottom paint we scuffed the epoxy with 100 grit sandpaper. After two coats of bottom paint Eurisko was blister-free and ready for the water. And we had survived three summer months on the hard in Trinidad. Neither task was easy, but both were worth the effort.


Ready for the water
Previously published in Sail Magazine

Our composting head debate has entered another phase. The creator of C-Head composting toilets has entered the discussion. MONDAY we'll hear about this third option.

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