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Old 10-12-2022, 09:32   #1
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Condensation under mattress

Hello y’all, so I’ve had a memory foam mattress on board for about 5 years (not the same mattress the whole time) and this winter I’m having an issue I’ve never had before. So under the mattress there is a decent amount of water that seems to be condensation (no leaks of any kind). I’m in New Orleans La and the humidity is high but the temp swings from 40-70 almost weekly during the winter.
Never had this issue in S Fl when on anchor for many years or during the summer.
Any ideas on ways to prevent this from happening?
Thanks
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Old 10-12-2022, 09:39   #2
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Re: Condensation under mattress

I went through this when living aboard. Your body puts out a lot of heat, creating condensation ......rather amazing actually.
I tried various things. One thing that was easy is I put 'DriDek' lock together plastic open grating under the mattress.

But you need a bit of air circulation for it to help more. So if the mattress seals the front edge against a trim piece at the V berth or berth entry, not much air circulation happens. It does keep the mattress out of the water though.

Next I cored a bunch of holes in the v berth plywood covers with a hole saw.
I then opened up the front v berth compartment door so the air could flow. Not all boats have a door there though. But a plastic vent could be installed.
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Old 10-12-2022, 09:40   #3
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Re: Condensation under mattress

I use the waterproof flooring under in gyms etc. open allows air but supports the mattress cheap too
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Old 10-12-2022, 10:01   #4
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Re: Condensation under mattress

if you can plug in then get a dehumidifier.
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Old 10-12-2022, 10:21   #5
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Re: Condensation under mattress

a. Memory foam is bad for this. It is not recommended for boats or any high-humidity environment. You probably need to wrap it, after drying completely (not possible on a boat--would need to be in a dry room for a week with no one sleeping on it).



b. The moisture is mostly coming from your body, through the mattress. Sealing the mattress works, but then you will need a topper.



c. Condensation is caused by a cold surface. Insulate the bunk base by covering with closed cell foam, sealed to the surface (so moisture cannot get behind it). Yoga pads. Self adhesive insulation. Foam gym tiles (not the open shower type).


Ventilation will not works as well as getting rid of the cold surface that is causing the condensation. Obvious. You don't dry a cold glass of ice water by blowing a fan on it, you do it with an insulated cover.


(Yup, I lived on board for a short time in real, sustained, sub-freezing winter.)
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Old 10-12-2022, 10:55   #6
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Re: Condensation under mattress

Quote:
Originally Posted by thinwater View Post
a. Memory foam is bad for this. It is not recommended for boats or any high-humidity environment. You probably need to wrap it, after drying completely (not possible on a boat--would need to be in a dry room for a week with no one sleeping on it).



b. The moisture is mostly coming from your body, through the mattress. Sealing the mattress works, but then you will need a topper.



c. Condensation is caused by a cold surface. Insulate the bunk base by covering with closed cell foam, sealed to the surface (so moisture cannot get behind it). Yoga pads. Self adhesive insulation. Foam gym tiles (not the open shower type).


Ventilation will not works as well as getting rid of the cold surface that is causing the condensation. Obvious. You don't dry a cold glass of ice water by blowing a fan on it, you do it with an insulated cover.


(Yup, I lived on board for a short time in real, sustained, sub-freezing winter.)
Your body puts out a lot of heat and moisture when you are not in bed. You dont get soaking wet because of ventilation.

There's a reason why industrial flood recovery services like Serv-Pro use a multitude of large fans.
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Old 10-12-2022, 11:32   #7
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Re: Condensation under mattress

I put hypervent under my foam mattress. It did help
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Old 10-12-2022, 12:12   #8
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Re: Condensation under mattress

Quote:
Originally Posted by Cheechako View Post
Your body puts out a lot of heat and moisture when you are not in bed. You dont get soaking wet because of ventilation.

There's a reason why industrial flood recovery services like Serv-Pro use a multitude of large fans.

Ventilation can work if it is cool. Insulation works better if it is actually cold. Your analogies are correct ... but not comprehensive. For example, a dehumidifier uses a fan to force air past a cold surface to increase condensation. True. Serv-Pro fans work because the air is relatively dry, something that is uncertain in a boat. Also, the floor is only cool, not actually cold. So which approach is more effective depends on the variables (relative humidity, temperatures, and airflow rates). Neither of us is wrong, and in most cases, either method will work.


I my case insulation was far more effective and efficient because I was in a colder climate. You can't ventilate you way around a very cold surface. It just drips more. Consider the glass of ice water. On the other hand, air alone is sufficient on a lightly fogged window ... if the air is not too humid (the car dehumidifier will not allow recycle, only fresh air, for this reason).



The vapor barrier placement in a home (on the inside, to keep moisture OUT of the insulation) is based on this.
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Old 10-12-2022, 12:29   #9
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Re: Condensation under mattress

Thinwater's right, again!

For a while, we used Chinese seagrass doormats, linked together for each side of the bed.

When Jim decided he didn't care for the smell, we donated them, and they got repurposed as fender mats for timber boats.

We went to a rubber store and bought closed cell foam, about 1/4" thick is all, and bonded it to the underside of the mattress, and have had no trouble since. However, it is not memory foam, just commercial quality bed foam.

Incidentally, in normal conditions irrespective of normal humidity, one exhales about 1 cup of water each day, and if the boat's closed up, it has nowhere to go but to condense out. That's a quart every 4 days throughout the cold weather. It doesn't go away when it "dries out" in the warmer time of day: the warmer air absorbs the moisture, but cannot hold it when the temperature drops. It fills up your bed.

Look carefully at the mattress ticking. If it has mildew, you would be wise to buy something different, AND will still need the closed cell barrier glued to the underside of the mattress.

Fwiw, there is another under the mattress system that is often touted here on CF, by the name of Froli. We have not tried that, so no personal knowledge of it.

Ann
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Old 10-12-2022, 14:28   #10
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Re: Condensation under mattress

Hypervent is one ventilation product, marketed into the marine product. There are others marketed to RVers. They work. But they are just roof ventilation mat, meant to under wooden shingles. Cheap if you buy a roll, way more by the foot. Maybe you have some friends and you can divvy it up and do whole boats (salon cushions and all).



https://www.homedepot.com/p/39-in-X-...DAIR/311222526


I have a couple samples in my basement, but I have not gotten around to testing them. Some are stronger than others. Some come with an attached vapor barrier.
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Old 11-12-2022, 08:38   #11
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Re: Condensation under mattress

Hypervent has worked well for us for a dozen years or more. Yes, it is a bit pricey but it is a one time expense and solves the problem of wetness under the mattress. I suggest, after cutting it to fit, you tape the edges.
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Old 11-12-2022, 09:35   #12
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Re: Condensation under mattress

Check out the Froli sleep system. Very effective, comfortable, highly adaptive and an excellent company to work with.
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Old 11-12-2022, 11:14   #13
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Re: Condensation under mattress

We frequent cold climes (>57°N) and have spend winters onboard in consistent below zero °F, with multi-week periods in the -20s °F.

We have found a combination of insulation and ventilation (against any cold surfaces the mattress {and upholstery cushions} touches- including the vertical sides), Hypervent on top of or underneath the insulation (more below), and a high quality waterproof, hypoallergenic mattress encasing cover works very well.

The reason we don't install insulation first (and seal all edges) is we always have storage under our berths that needs to be accessed on occasion.

After decades of living aboard several different boats over winter, our current (and very successful) approach is:

-Hypervent (or equavilent) under and up any mattress sides that are close to any surface (e.g., hull, cabinets, etc.)

-Thermarest style air mattresses for camping on top of the Hypervent. (Great insulation, and quick to remove {and replace} for other uses- including camping, unexpected guests, and lounging on deck.)

We have also used the closed cell foam camping mats with a zig-zag cross section where Thermarests didn't fit or make sense. Those work well and have a tendency to trap debris and any errant moisture in the little valleys, making them easy to clean and keeping the debris and small moisture beads away from the mattress/cushion bottom.

-A high quality hypoallergenic, waterproof mattress encasing cover. (Ones that encase the entire mattress- all 6 sides- including the underside... Likewise for all pillows...)

The goal is to prevent water vapour from being able to enter the mattress (or pillow or cushion) material due to body heat and perspiration/respiration; insulate under the mattress where our bodies lay; and ventilate under the insulation and along any sides close to the mattress.

In case any this is useful.

Cheers! Bill

PS: We have many other posts written in the past about living on a boat in cold weather in case any of them are of interest.
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Old 11-12-2022, 17:14   #14
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Re: Condensation under mattress

I am from Louisiana and speaking from experience, ventilation is the solution. I use Hypervent type matting under the mattress.
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Old 11-12-2022, 19:01   #15
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Re: Condensation under mattress

This slatted bed base from IKEA privides ventilation and greatly improves the bed’s comfort. Trim the slats with a saw to fit.

https://www.ikea.com/us/en/p/luroey-...base-00160215/
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