Using anti condensation paint on platsic surface

[Owen74]

Hi, can I paint Dryzone anti-condensation paint (or similar) on a plastic surface, or will it corrode/harm the plastic in some way?
This will be on the underside of plastic roof channel which is prone to condensation, so I can't risk harming the plastic.
I don't have a 'spare' area to test it on, so I would welcome some opinions before I try it. Thanks.

Dryzone Anti Condensation Paint

• Thermal Effect - microsphere tech • Anti-condensation Paint • Increased time-to-condensation• Interior use onlyDryzone® Anti-Condensation Paint has been specifically designed to reduce condensation from forming on treated surfaces. The glass microspheres in the paint increase the time to...

www.toolstation.com

 

[JohnD]

Where is the water vapor coming from, and why don't you ventilate it away?

 

[Owen74]

Where is the water vapor coming from, and why don't you ventilate it away?

Presumably it's coming from the air in the loft space which is slightly warmer than the freezing temp outside, and condenses on the thin plastic surface. I have soffit vents, lap vents and insulation, but nothing stops this. I have had some success covering the plastic with SuperFoil but I think a couple layers of anti condensation paint would be more effective. Just don't know if it's OK to use on plastic.

 

[JohnD]

You say it's a loft?

Paint is not the answer. It will not take the water vapour away.

CONDENSATION IN LOFT (ANSWERS)

This seems to be the time of year for condensation in lofts, so instead of replying to lots of queries I though I would write this "one-size-fits-all" post. Please also see //www.diynot.com/wiki/Building%3ACondensation-in-Houses Condensation in lofts occurs when the amount of water...

www.diynot.com

 

[Owen74]

You say it's a loft?

Paint is not the answer. It will not take the water vapour away.

CONDENSATION IN LOFT (ANSWERS)

This seems to be the time of year for condensation in lofts, so instead of replying to lots of queries I though I would write this "one-size-fits-all" post. Please also see //www.diynot.com/wiki/Building%3ACondensation-in-Houses Condensation in lofts occurs when the amount of water...

www.diynot.com

I know it won't take the vapour away but it will stop it condensing on the roof valley and dripping into woodwork.

I have lots and (I mean lots) of ventilation up there.

I have added more soffit vents and lap vents.

I have pulled all the insulation away from the soffet vents.

I have added more insulation.

The problem is the plastic roof valleys are exposed inside the loft, and sit against beams, and have nothing insulting them from a temperature difference. When cold outside and less cold on the inside, condensation happens. The loft is very drafty and cold which it should be.

The condensation is only a problem on these plastic roof valleys.

If you have suggestions then please share as I need all the ideas I can get.

 

[JohnD]

If you have suggestions then please share as I need all the ideas I can get.

I just did.

 

[Owen74]

I just did.

Thanks, I had already read through the condensation FAQ a few times before posting this, unfortunately it doesn't cover my situation which is a bit unique (and uniquely annoying). The plastic roof valleys for some reason in my loft have no membrane under them, they are fully exposed, and the condensation is literally only on these.

This post was just to check if anti condensation paint is OK to use on that plastic. But for the orignal cause, I think it comes down to a build error. Pics and details of my problem are here:

Plastic roof channels/valleys - condensation issue

Hi, I'm hoping somebody knows an easy fix for this. Our house has a small two-storey extension at the front so there are now two adjoining sloped roof sections on the house (see pic). All is fine but there's one problem. The two roof sections have plastic (not lead) roof valleys/channels...

www.diynot.com

Since I cannot rebuild the roof, and I already have loads of ventilation, it seems my only option is to insulate the valleys themselves.

 

[Wayners]

Cover the plastic in insulation?

 

[opps]

Hi, can I paint Dryzone anti-condensation paint (or similar) on a plastic surface, or will it corrode/harm the plastic in some way?
This will be on the underside of plastic roof channel which is prone to condensation, so I can't risk harming the plastic.
I don't have a 'spare' area to test it on, so I would welcome some opinions before I try it. Thanks.

Dryzone Anti Condensation Paint

• Thermal Effect - microsphere tech • Anti-condensation Paint • Increased time-to-condensation• Interior use onlyDryzone® Anti-Condensation Paint has been specifically designed to reduce condensation from forming on treated surfaces. The glass microspheres in the paint increase the time to...

www.toolstation.com

I think you need to email DryZone.

They say that it takes longer for the condensation to form but if it takes hours, rather than 1, have you really gained anything?

 

[JohnD]

So water vapour is getting into the loft somehow.

It will not be the cold outside air bringing it in, it will certainly rising from your house, or coming from a leak.

If you say you have no ceiling holes for pipes and downlighters, you have closed and sealed the loft hatch, you don't have a steamy bathroom or wet washing, and you have no pipes, tanks or roof leaks, then I don't know where it's coming from.

You need to find where it is coming from and repair it.

Paint will not make the water go away.

 

[Owen74]

So water vapour is getting into the loft somehow.

It will not be the cold outside air bringing it in, it will certainly rising from your house, or coming from a leak.

If you say you have no ceiling holes for pipes and downlighters, you have closed and sealed the loft hatch, you don't have a steamy bathroom or wet washing, and you have no pipes, tanks or roof leaks, then I don't know where it's coming from.

You need to find where it is coming from and repair it.

Paint will not make the water go away.

OK yes I get all that, but is it not possible that regardless of insulation and ventilation, an exposed thin plastic sheet (the 3mm roof valley), with outdoor weather on one side, and loft air on the other, is simply prone to condensation? So I'm looking to 'thicken' or 'insulate' that plastic so air doesn't condense on it.

The loft feels cold and drafty, I can feel air moving and see cobwebs wafting in the breeze. But it will always be *a bit* warmer than outdoors won't it?

Never had this problem before these roof valleys were put in. The problem I believe is a build error; a thin plastic roof valley, not covered by felt or membrane of any kind. Just a 3mm plastic strip exposed both sides. It can't be good enough like that, surely.

I'd add, I've monitored closely and the problem only happens during cold/wet weather, does not happen especially during certain times of day (eg bathtime or when heating comes on), and I don't see condensation anywhere else in the loft space.

That said, I'm going to hunt round up there one again time in case I missed any seals. And I will double check again that nothing's blocking any vents.

 

[robinbanks]

I have had some success covering the plastic with SuperFoil

At what thickness?

The multifoil industry really wants the product to work, but it persistently falls short of its performance claims, sometimes outrageously so. SuperFoil's website claims that their thinnest product outperforms kingspan by 25% (yet bizarrely their thickest products do not)

To attract condensation a surface needs to fall below 14 degrees C. In your loft, with all its wood, felt, battens and tiles with the air pockets they create you have a construction that has a store of heat (in the tiles; they're heavy/dense and when warmer will take relatively long to cool) and a layer of insulation formed by the air gap trapped by the felt. The surface of the felt will be far more likely to stay above a dewpoint for longer than a thin sheet of plastic directly connected to the outside world. The plastic will thus become something like a dehumidifier element; a cool section on which water vapour will condense. Also, don't forget that modern felts are breathable and will transmit water vapour as well as offering up a surface to condense on so they will resist condensation forming while they're able to transmit nearby vapour

Your plastic valley will forever be the point that attracts condensation first; if you're having a problem with it forming to excess and then running down the underside and dripping off making some area of the inner structure damp you can look to insulate it (and I'd use a product less reputed to be snake oil), double check that you don't have anything admitting warm house air into the roof space (we recently had pics of a bathroom extractor that just vented into the loft, but at first glance it looked like it was exiting, turned out to be that the pipe was run to the eaves and terminated inside), and clear a path for run off condensate so it doesn't affect vital parts of the structure, because you may always get it to some degree in certain weather conditions unless you're putting a good thickness of insulation to combat the plastic's inability to retain heat/the speed with which it tracks world temperature

 

[mrrusty]

Air in the house will be typically 20 degrees and 60% RH. If it gets in the loft space the same air will be perhaps down to 12 degrees because the ceiling is insulated, the loft is cold, and very close to the dew point. Any further cooling or surfaces at a lower temperature and liquid water will condense out.

Where can it go? the only place it can go is to be evaporated away by moving non-saturated air through ventilation. Breathable roof membranes are designed to take the nuisance of liquid water away - the wet air can get through the membrane, condense on the underside of the slates or tiles and the air movement in the ventilated space between eaves and ridge evaporates the condensation away. The membrane traps any dripping liquid water and prevents it wetting the roof structure and loft contents.

To control condensation you have to consider the complete system. Even if you prevent condensation in one spot, if the air is saturated it will condense somewhere else.

 

[Owen74]

At what thickness?

The multifoil industry really wants the product to work, but it persistently falls short of its performance claims, sometimes outrageously so. SuperFoil's website claims that their thinnest product outperforms kingspan by 25% (yet bizarrely their thickest products do not)

Yep, sounds about right. I have the 3mm SuperFoil. I experimented and found that a single layer has limited effectiveness, just attracts a thin layer of moisture on top. But if I double up with 2 layers it is pretty much bone dry.

I think anything is better than bare exposed plastic with outdoors on one side, indoors on the other. If the builders had put felt under the roof valley this wouldn't have been a problem.

Another idea is to stuff loft insulation over the top instead of SuperFoil, or in addition to it. I might experiment with that next.

 

[Owen74]

Your plastic valley will forever be the point that attracts condensation first; if you're having a problem with it forming to excess and then running down the underside and dripping off making some area of the inner structure damp you can look to insulate it (and I'd use a product less reputed to be snake oil),

Yes, that's what I'm realising. The exposed cold plastic valley effectively becomes a dehumidifier, condensing loft air on its underside and running it down to the gutter. Which would actually be fine if it didn't run next to wooden supports, dripping all over them.

I'm pretty sure if I can insulate the plastic I will not see condensation anywhere else, because nowhere else has a surface that faces outside and another inside. It's the fact the plastic becomes freezing cold during rain or cold weather, which makes it prone to condense air with even slightly warmer temps inside the loft.