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Blisters

 
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merwin10
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PostPosted: Thu Mar 06, 2008 9:08 pm    Post subject: Blisters Reply with quote

OK Terry -

Need your help? stripped the hull and found some small bilsters this year! Please explain what is happening and the proceedure to fix them!

Mike - Crying or Very sad
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PostPosted: Fri Mar 07, 2008 9:59 am    Post subject: Reply with quote

OK Mike, I'll try to not get too technical here: the principle cause of blisters is the presence of water soluble materials in the hull laminate As water molecules penetrate the laminate they combine with these materials to form a droplet of solution. Because of osmotic pressure (Osmosis is the tendency of two liquids of different concentration, when separated by a semipermeable membrane, to mix), more water molecules combine with this droplet, eventually expanding enough to cause a blister.
The solution formed by water mixing with the water soluble materials in the laminate is acidic, and more concentrated than pure water. Thus water molecules pass through the membrane to combine with the more concentrated liquid. (The semipermeable membrane in this case is the fiberglass laminate). The new mixture attracts more water, expands, and causes the blister.
Stress, whether from water absorption in the gel coat or from the rigors of the sea, could also be a culprit, with water soluble materials concentrating in microscopic cracks or at interfaces between layers of laminate. A third kind of blister is also possible: the long-term effect of water saturation of the laminating resin. Most of us don't think of our fiberglass boats as having the characteristics of a sponge, but studies have demonstrated that fiberglass laminates do indeed absorb water.

OK, now that the chemistry lesson is over lets fix your blisters
1) Open up the blisters with an exacto or razor knife. Make sure to stay well away from the blisters when you pop them, as the liquid inside the blisters is acidic -- you definitely don't want to get any of it in your eyes.
2) MOST IMPORTANT!!! Let the blisters dry out completely.
Sand the blisters down to the fiberglass matting, until no sign of the blister is apparent.
3) Clean the area with acetone or similar product.
4) Fill the blistered area with an epoxy-based blister repair product. For this step, I would use a product like MarineTex.
5) When the epoxy is completely dry, sand and fair down the surface so that it is nice and smooth.
6) Once the repair has been faired out, clean the area with acetone or similar product.
7) Apply a barrier coat with a roller. This should be at least 5-mils thick (3 coats dry is about 5-mils or 5 thousands of an inch thick)
Cool Once the barrier coat is dry, apply a bottom paint with a roller.

There are many different barrier coats available and I really dont have a preference as to one over the other but having this barrier coating is next to painting the bottom of your boat every 2 years, the best thing you can do to stop and prevent the blister formations.

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merwin10
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PostPosted: Fri Mar 07, 2008 10:10 am    Post subject: Reply with quote

Hi Terry -

Ok got it! I do have a question you said to use marine-tex as a filler then paint it with a barrier coat 3 coats. I didnot read to gel coat the marine-tex to match the rest of the bottom. I assume that this is because it will be covered with 3 barrier coats and at least 2 top coats of bottom paint. I assue that marine-tex does not need a water barrier that the normal epoxy does - which is what the gel coat is all about it is a water tight barrier.

Mike - Rolling Eyes
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PostPosted: Fri Mar 07, 2008 10:21 am    Post subject: Reply with quote

Sorry your right, The barrier coat is going to cover and seal the repair area and seal the rest of the bottom of the boat hull. Then when the bottom paint is applied, it will all be one color. You can of course gel coat the repair area if you want to match the rest of the hull but a good barrier coating eliminates that need.
I like to use marine-tex as its an easy to apply epoxy putty that has been formulated for use below the water-line. makes for easier sanding, same goes for applying the coatings with a roller, a nice uniform layer thats easy to sand if needed.
Please keep in mind that this type of repair isnt all that hard, BUT and its a big one, you MUST wait until the area is completely dry before you apply the filler or you will have the blisters come right back. Now, if you pop the blister cover off completely, you will have a rough area of exposed fiberglass matting to check with a moisture meter and to help the epoxy bond, but sanding first will remove any dirt, wax or bottom paint that will hurt the bond strength
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PostPosted: Fri Mar 07, 2008 10:36 am    Post subject: Reply with quote

This is from the Marine-tex website:

Can I apply Marine-Tex in dry conditions on a below-the-water-line application?

Yes, the Marine-Tex is an excellent choice for repairing gouges or holes that are located below the water-line. Once cured, Marine-Tex is impervious to water and many chemicals. Since putties will go only where they are placed, be sure that the Marine-Tex has completely encapsulated the problem area. It is a good idea to sand the perimeter of the repair so that the Marine-Tex achieves a grip on the solid surface around the repair. Laughing
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rebait
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PostPosted: Fri Mar 07, 2008 9:44 pm    Post subject: Reply with quote

Mike,

I can vouch for the strength and durability of Marine-Tex. I have been using it since the 70's. First I used it for "glueing" reel seats on fishing rods. The biggest test was on my 18' center console when the sections of the gel coat and "chopper gun glass" on the top of the gunnels failed. I had holes up to 3/8" here and there. The dealer & manufacturer said it was off warranty so it became my problem. I used white Marine-Tex and not only did it match the color but the repairs were done over 25 years ago and you have to look close. I have used it below the water line to fix a scrape from a trailer roller that broke. I can't say anything negative about the product. Whenever I made a repair I made sure that it was completely dry to keep the glass from "wicking" or drawing water or moisture. Terry, I am sure glad to hear from a chemist that I did the job right from the start because I had my doubts when I first did it in 1982. I have found many uses for this product and it never ceases to amaze me.

John
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PostPosted: Fri Mar 07, 2008 11:00 pm    Post subject: Reply with quote

Yeah I love the stuff, easy to work with and if the repair area is prepped right, it will be stronger than the original. You can use it to get real smooth corners, can use it with fiberglass cloth, seals itself from water, cant say enough. I am filling in all the screw holes on my railings with it this spring since they are still dripping. I'm going to drill them out bigger and then fill the holes with it, then I can drill new holes same size as the original. I dont have a worry in the world about the marine-tex weakening the strength of the mount
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merwin10
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PostPosted: Sat Mar 08, 2008 8:46 am    Post subject: Reply with quote

Hi Guys -

Well again the site pays off with knowledge gain from others that have use a product that works and will correct the situation -

Thanks for the input -

Mike - Wink
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PostPosted: Sat Mar 08, 2008 9:48 am    Post subject: Reply with quote

Mike Good luck with the repair, Its always disheartening to find boat pox when doing the bottom. I would cut the blisters now and let them start draining so that you can repair them as soon as it gets warmer
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merwin10
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PostPosted: Sat Mar 08, 2008 4:56 pm    Post subject: Reply with quote

Actually I started popping them last year the ones I found! I figured that the less the acid solution was in there the better and the winter fresh water from rain and snow could only help - My only concern was that the acid solution most likely had a lower freezing point than water - Fiberglass mat soaked with water and then freezing can't be good, something has to give! We will see as right now it is pouring out - Fortunately we have had a warm winter the ground isn't even frozen!

Mike - Rolling Eyes
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PostPosted: Sat Mar 08, 2008 8:58 pm    Post subject: Reply with quote

usually what would happen is the water would freeze and cause a crack to appear. Never checked the freezing point of water that was acidic but dont think its different than normal water. With all of the pollution most rain is acidic now anyways, hence the term acid rain
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leokow
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PostPosted: Mon Mar 10, 2008 8:51 pm    Post subject: Reply with quote

Hi Mike, I had the same problem on the bottom of Overdue a few years ago.Only along with the blisters I had a lot of crazing of the bottom gel coat. Terry is right about the drying,its the most important part of the preparation. Most places recommend opening all the blisters when she is pulled from the water in the fall and let it completely dry out over the winter. A good way to check for moisture is to tape a piece of clear plastic over about a foot square area just taping around the edges in a few different places under the boat, wait a couple of days and see if any moisture accumulates in the space between the plastic and the hull. If not
then the hull should be dry enough to proceed. I used a product from Interlux called interprotect 2000(I believe)the barrier coat is formulated so that when it sets up the micro plates in the mixture overlap each other like roof tiles and prevent water from penetrating the hull,after applying the proper amount of material I then proceeded to cover with 4 coats of micron csc with biolux. If you use this system it's very important to apply the first coat of bottom paint before the last coat of barrier coat is completely dry(tacky),this locks the two of them together permenantly. You can then proceed at your leisure to apply the remaining coats of bottom paint. When I used this system on my boat it had been 4 years before I had to start to retouch some of the wear spots on the bottom paint. We did 3 boats like this Mike and had the same results with all 3 boats, it is truly a good system, and the instruction booklets are very explicit.I wouldn't recommend it Mike if I hadn't had such good results with the product...Good luck.. .LEO
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merwin10
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PostPosted: Tue Mar 11, 2008 8:49 am    Post subject: Reply with quote

Leo -

Thanks for the information, it is always nice to hear about something that works well! From the size of the problem I don't think the baot will hit the water much before July needed the hot weather to dry things out well enough to complete the task properly! That is ok though because with my family issues boating is on the back burner for the time being!

Mike -
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