foam backed vinyl stops condensation?

[chrisbitz]

I've been having a lot of problems with condensation on the inside of my boat, and I got thinking...

I think condensation happens when warm inside air touches cold surfaces, like the inside of the roof or the hull. So I was thinking, why not get some 2/3mm polystyrene on a roll, and stick it to the fibreglass, then the warm inside air will only touch the insulated polystyrene...

then it slowly dawned on me that this may be what foam backed vinyl is for.. I'd always assumed it was to hide surface imperfections, but I have a feeling that it may well be to insulate a little and stop condensation?

Would my boat, when brand new in 1978, have had such bad condensation, or is it just that the foam has crumbled off now after so many years, and not insulating at all?

Am I barking up the wrong tree here? I'm not so much worried about heat loss, more the problem of waking up and finding everything at the edges is wet!

Can you get insulating foam backed vinyl, or is it all the same sorta thing?

 

[Storyline]

You could try Hawke House http://www.hawkehouse.co.uk

 

[geem]

To vastly reduce condensation you need to use 2 layers of 6mm closed cell foam (light sleeping mats) then put your foam backed vinyl on top. I ran this through our computer software a few years back to ensure I got the thickness right.
I insulated our catamaran at the time to this standard and it made an amazing difference to the temperature and condensation was a thing of the past. You have to remove any glue from the hull with a wire brush on an angle grinder thn fix new with high temp contact adhesive. It's a big job to do correctly and neatly. We did our whole boat and added 2tons of positive buoyancy by the time we had finished!

 

[boatmike]

Geem is correct. Foam backed vinyl won't stop condensation. It will improve things a bit but you need more. Consider reducing moisture by fitting a dehumidifier if the boat is entirely closed up, or if not simply increase ventilation if you don't want a dehumidifier running all the time. It will also be worse when you are sleeping on board and close up all the hatches to keep warm.... You actually create an incredible amount of moisture by breathing...... Don't try holding your breath though, it has other detrimental effects.....

 

[Deleted member 36384]

I replaced carpet with foam back lining stuck to the GRP hull. The condensation was still there. To remove it you need an air gap between the hull and the foam backed lining.

 

[JumbleDuck]

Would my boat, when brand new in 1978, have had such bad condensation, or is it just that the foam has crumbled off now after so many years, and not insulating at all? ...
Can you get insulating foam backed vinyl, or is it all the same sorta thing?

Westerly by any chance, sir? Despite what others have written, I never found any condensation at all on the foam backed vinyl when I had a boat which used it. Hawke House, as recommended, have templates for most boats on file. Replacing it is a horrible, horrible job. If your boat is a Centaur, try flogging it to Dylan Winter and buy another with the headlining done.

 

[bedouin]

Foam backed vinyl will help to reduce condensation and it is well worth doing - but won't cure it on its own. If you are sleeping in the cabin then the only way to eliminate condensation is with good ventilation.

 

[Iain C]

Whist I won't argue with the science, I also have found that the extra insulation is unnecessary if using good quality foam backed vinyl. That said, my main roof lining is on plywood panels so I do have an air gap. My focsle and quarterberths are lined with a felt style van lining which works very well. My only issue is that I still get loads of condensation on my windows, and there's no way round that really!

 

[macnorton]

Whist I won't argue with the science, I also have found that the extra insulation is unnecessary if using good quality foam backed vinyl. That said, my main roof lining is on plywood panels so I do have an air gap. My focsle and quarterberths are lined with a felt style van lining which works very well. My only issue is that I still get loads of condensation on my windows, and there's no way round that really![/QUOTE

I have screen covers made from canopy material with insulation sewn in, clipped over the outside of the glass with press studs.
Keeps the boat cool in the summer as well.

 

[Seajet]

My boat has varnished thin ply sheets on the deckhead; I fitted polysyrene tiles and silver foil between ply and coachroof, the silver foil to hopefully give an unscientific enhanced radar signature as well as insulation.

I only get condensation on the windows when the cooker is on, otherwise fine.

There used to be ' International Korkon ' anti condensation paint, which basically had small bits of cork in it, don't know if it's still available; when I tried it in the forepeak in about 1979 I found it gave a very hard rough finish, rubbing any bare skin on it was like being surformed and a right passion killer !

 

[geem]

I replaced carpet with foam back lining stuck to the GRP hull. The condensation was still there. To remove it you need an air gap between the hull and the foam backed lining.

This is not strictly true. The condensation occurs when warm moist air comes into contact with a cold surface that is below the dew point of the moist warm air. If you remove the cold surfaces so those surfaces are above dew point then you don't get condensing. By insulating with closed cell foam insulation you achieve two things; You create a vapour barrier to stop the warm moist air getting to the cold hull and the surface of the insulation facing the cabin is warm enough to not condense. It is important that when you line the cabin with closed cell foam that you don't have gaps where the cabin air can get to the hull. You do this by using two layer of 5 or 6mm foam and stagger the joints or you use self adhesive aluminium tape to tape the joints.
Having an air gap behind insulation can in itself create an insulating layer but if the air gap is ventilated to the boat it is likely to condense. Houses used to have air filled cavities for insulation. These days they have partial fill of complete fill insulation in them for thermal benefits.
With a well insulated and vapour sealed boat to about 12mm open cell foam backer vinyl you will have a warm dry boat needing less heating. Keep some dorades open to increase the dry air entering the boat and it will stay condensation free.
You can't do much about windows unless you add some cling film to them with a hair drier to tighten them up

 

[Hadenough]

This is not strictly true. The condensation occurs when warm moist air comes into contact with a cold surface that is below the dew point of the moist warm air. If you remove the cold surfaces so those surfaces are above dew point then you don't get condensing. By insulating with closed cell foam insulation you achieve two things; You create a vapour barrier to stop the warm moist air getting to the cold hull and the surface of the insulation facing the cabin is warm enough to not condense. It is important that when you line the cabin with closed cell foam that you don't have gaps where the cabin air can get to the hull. You do this by using two layer of 5 or 6mm foam and stagger the joints or you use self adhesive aluminium tape to tape the joints.
Having an air gap behind insulation can in itself create an insulating layer but if the air gap is ventilated to the boat it is likely to condense. Houses used to have air filled cavities for insulation. These days they have partial fill of complete fill insulation in them for thermal benefits.
With a well insulated and vapour sealed boat to about 12mm open cell foam backer vinyl you will have a warm dry boat needing less heating. Keep some dorades open to increase the dry air entering the boat and it will stay condensation free.
You can't do much about windows unless you add some cling film to them with a hair drier to tighten them up

Spot on! You need to get rid of voids and use closed cell foam. Speaking of which, I need to insulate some voids I can't access and am trying to source an applicator for closed cell which I assume will be two pack. Any ideas?

 

[Hydrozoan]

I've been having a lot of problems with condensation on the inside of my boat, and I got thinking...

I think condensation happens when warm inside air touches cold surfaces, like the inside of the roof or the hull. So I was thinking, why not get some 2/3mm polystyrene on a roll, and stick it to the fibreglass, then the warm inside air will only touch the insulated polystyrene...

then it slowly dawned on me that this may be what foam backed vinyl is for.. I'd always assumed it was to hide surface imperfections, but I have a feeling that it may well be to insulate a little and stop condensation?

Would my boat, when brand new in 1978, have had such bad condensation, or is it just that the foam has crumbled off now after so many years, and not insulating at all?

Am I barking up the wrong tree here? I'm not so much worried about heat loss, more the problem of waking up and finding everything at the edges is wet!

Can you get insulating foam backed vinyl, or is it all the same sorta thing?

I would be very surprised if a few mm of foam backing on vinyl headlining makes much if any difference to the extent of condensation - as opposed, perhaps, to hiding it - which is not the same thing! I've replaced foam backed headlining on ply boards with plain vinyl: I prefer the 'clean' look and wanted to avoid any future sag problems. I use a dehumidifier when on board in winter - as someone else has said, one generates a lot of moisture just by breathing, which is hardly optional.