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  #1  
Old 12-11-2002
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True Grit

I''ve been checking around with several yards about doing a bottom coat job on my boat.This will only be the third she has had new bottom coat since I''ve had her.When I pulled her out recently, I discovered about half a dozen quarter size blisters.One yard that quoted doing the work mentioned that they would sand-blast the bottom,repair the blister areas,apply two barrier coats,and then two bottom coats.All this sounds good to me with the exception of the sand-blasting.The other yards mentioned sanding.Is sand blasting an acceptable means for removing the old bottom coat?
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Old 12-11-2002
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Sandblasting with sand, is not an acceptable way of removing bottom paint and blisters as it requires very great skill to keep the bottom of the boat fair. Generally softer cutting agents are a little better for that kind of thing. The good news about blasting is that it does not build up localized heat which can promote ongoing blister problems.

Frankly with only 6 quater sized blisters, I would suggest repairing just those blisters, in which case sanding is fine.

As to bottom paint build up, the yard should be removing multiple layers of bottom paint when they sand for the first coat of each bottom job so that the boat does not become ''paint sick''. With the high speed air driven sanders that are so common these days this should not be a problem.

Jeff
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Old 12-11-2002
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True Grit

Thanks for the reply Jeff.After reading it, I realized that I left out some information in my original post that is important.The boat never had barrier coat applied after it was built. The manufacturer apparently applied two coats of bottom paint over the gell coat, and sent her on.(possibly because they knew the boat would be kept in freshwater and thought bottom coat would be sufficient,...I don''t know.)Being naive as I was at the time, I didn''t know the boat only had bottom coat on her.When I pulled the boat out a year ago to have her bottom done, I found the blisters.I had scheduled to have bottom coat reapplied at a local yard thinking that this was all that would be needed, but after seeing the bottom, it was obvious that the boat only had bottom coat.When they saw the bottom, they suggested the sand-blast,repair blisters,two barrier coats,and two bottom coats route.To make a long story shorter, they didn''t have time to do all this work due to continual bad weather before I needed the boat for a pre-scheduled trip.At the yards suggestion,I opted to have them apply one coat of bottom paint while leaving the blisters in tack.The extended plan was to pull the boat upon return from my trip and then do the more extensive work.This is where I''m at now in this process.The bottom line is I want to have it done right this time.Please advise again.Thanks!
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Old 12-11-2002
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First of all, Fresh water is more likely to cause blisters than saltwater. (The molecules are smaller and react more readily to form acids) So if you didn''t have blisters in fresh water that tells you a little (which is positive) about the quality of the glass work.

Let me guess, you prescheduled trip was not only into salt water but warmer water than the fresh water where the boat had previously been kept (OK, So I have just been watching a Charlie Chan movie)

Putting a barrier coat on is not a bad idea. If you decide to put one on the boat needs to be very dry. In other words, you need to strip the bottom down to the gelcoat (or beyond) and let it sit for months in a dry location. It is a big job to do right.

Bead or walnut shell blasting is a better technique than sanding because the heat from a major sanding job can accellerate or initiate a blister problem even in a boat that is out of the water but which has a reasonably high moisture content.

If I were in your shoes I would probably just repair the couple blisters that you have and monitor them at next haul out to see if the blister problems have progressed. If the problem abates, your home free. If it gets a little worse then make the necesary repairs. But if it gets much worse, then do a peel, and come back with epoxy and cloth which is the real way to do it right.

Respectfully
Jeff
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True Grit

How important is it to go all the way to the gel coat before putting on bottom paint? It looks like there were only two prior coats. It came off with a sanding block in different layers and unfortunately I used a power washer that also made it a little uneven. I talked with an amatuer who refinishes his own boat and he said the primary job is to sand off the ridges (make smooth transitions) and then make sure the paint is high quality and consider two plus layers. The boat will be kept in the water in a salt water environment. I will be only day/coastal sailing but hopefully use it several times a month.

Thanks,
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Thanks again Jeff for the info.Now I know what keeps you at the top of the game...Charlie Chann movies!I''ll have to watch more of them ;^)
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Old 01-22-2003
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Jeff H wrote:

"If I were in your shoes I would probably just repair the couple blisters that you have and monitor them at next haul out to see if the blister problems have progressed. If the problem abates, your home free. If it gets a little worse then make the necesary repairs. But if it gets much worse, then do a peel, and come back with epoxy and cloth which is the real way to do it right."
>
>
Please excuse my ignorance of the subject. The cure appears to be expensive. Is it worth the time and expense involved?

Other than the degraded appearance and possibly a minute loss of speed, what is the downside of ignoring blisters?
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Old 01-22-2003
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Your entire hull could delaminate.
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Old 01-22-2003
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What can be a merely expensive repair could become a more expensive repair than the boat is worth as you literally end up laminating a new bottom. The problem with blisters is that they expose the open ends of the glass fiber. This permits moisture to move deeper into the laminate and potentially create the kinds of pressure that pried the laminate apart and allows water even deeper access. Eventually you have what looks like a boat but which structurally is no longer a boat.

Jeff
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Old 01-23-2003
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So here is what I did. I had a bottom full of blisters that the previous owner had covered up with a nice thick layer of new gelcoat. Didn''t discover this until I went to repair what I thought was a few medium sized blisters. What a surprise. I used a pressure washer with a sand pick-up. The sand pick-up is a hose connected to the end of the pressure washer wand, it''s attached to a hose that goes into the bag of sand (you pcik the grit but talk to the sand supplier, they usually have the proper suggestions). The venturi effect of the high pressure water sucks the sand up the tube blows it into the hull. It''s very easy to control the impact against the hull simply by distancing the wand. There is NO dust! There is also no heat build-up. A word of caution through, it takes a lot of sand to do a 30 ft hull. The finished hull has a course surface (like sanding with 80 grip paper), perfect for the layers of repair epoxy and barrier coats. But befoe you go to this length, I would suggest that repairing the few blisters you have by hand would probably be the best bet.
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