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Old 12-02-2010, 20:32   #1
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Red face Inside Hull Sweating

the inside hull is sweating. It is painted fiberglass and the water is condensing on the walls. This occurs especially during weather change.

Any recommendations on how to solve this problem?

I am assuming that I have two choices - a vapor barrier outside or do something on the inside. I was thinking there is a material that looks like cooregated cardboard made out of either a PVC product or some other plastic. I have seen it used as packing material and was thinking that I could use West system to apply it just like it was a sheet of plywood that I was sheaving over the glass. Then I would put a finish of some type - i,e. carpet or paneling or wood, etc.

We are not talking about a small amount of condensation - this is so bad that it is getting out mattress wet and moulding and soaks our shelves. This all occurs above the water line. Thanks very much. Dutch.
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Old 12-02-2010, 21:07   #2
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You need to add enough insulation so the inside surface is above the dewpoint of the interior air. You need at least 1" of closed cell insulation that is as closely attached to the hull as possible. You cannot allow any voids, cracks or spaces as condensation will form inside the space. Strips of rigid foam (polyurathane, SM, isocyanate) works well if you install a 6 mil vapor barrier over it (seal all seams) and then install paneling over it.
Any areas where air circulation is restricted such as in lockers, or where anything such as a mattress lays against the hull use 2" or more insulation.

When we rebuilt the interior of our boat we installed 2 inches of closed cell insulation everywhere above the waterline, then a vapour barrier and finally wood. Never had a condensation problem (spent a winter in Cape Cod, Mass).
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Old 12-02-2010, 21:16   #3
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Well... if it is just for preventing condensation, I'm not sure if 1-2" is needed. But as you are insulating, why not to keep the cold out at the same time?!! So that makes the 1" a good choice.

Dutch, I would experiment with some small pieces. There are flexible types too, I have seen them used under the cement of tiled floors for example. That stuff is thin but give it a try. I would take a piece and use spray-glue to put it on. You can clean that up without too much trouble after the test (I think ;-)

I have seen 1/4" foam prevent condensation under a hatch. It was on the outside, between the hatch lens and a hatch cover. This is why I think that you don't need 1" but it's just a guess.

cheers,
Nick.
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Old 12-02-2010, 21:32   #4
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Thank you.

Is that silver covered stuff at Homdepot 1/2" and 1" closed cell insulation????


This hull covering job has readley become a pain in the back side.

Dutch
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Old 12-02-2010, 21:55   #5
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The silver covered stuff at Home Depot is closed cell insulation. Stay away from the white beaded stuff, it is garbage.
If you are where the temp drops to freezing use 1" of foam. Depends where you are (how cold) and if you keep the boat closed up for warmth and use propane for cooking.
Propane produces a lot of water. 1 lb of propane produces about 1.6 lbs of water. That is most likely where all the condensation is coming from. A fair bit comes from just breathing.
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Old 12-02-2010, 22:08   #6
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I live in NE Florida, it shouldnt have temp changes like this.

thank you for the help.

Dutch
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Old 13-02-2010, 02:09   #7
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I was working on a steel trawler that was sweating in the fxhole. The local chippy stuck a layer of used carpet up and that did it. Pretty agricultural but it did work. Mild climate here maybe like Florida.
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Old 13-02-2010, 19:40   #8
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Nansulate Home and Industrial Thermal Insulation and Asset Protection Coatings
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Old 13-02-2010, 22:07   #9
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Thank you all for the advice and I have decided to go with the 1" of closed cell insulation. It will help me in a number of ways and seams to be the cheaper way to go also.

Dutch
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