The PCA view of Condensation!

• Cold air enters the building
• The air is warmed for the comfort of the occupants
• The warm air takes up moisture
• The warm, moist air comes into contact with cold surfaces, walls, windows, etc. and is cooled below its Dew Point
• Condensation occurs as the excess moisture is released"

Lets just look at this bunch of seemingly realistic tripe.  Firstly, why is cold air entering the building the usual thing to happen first?

If cold air is entering the building, is it cold dry air (which is actually much more likely to happen in winter), or cold damp air (very unlikely in winter)...

Why is the warm air 'taking up' moisture?  Where did that moisture come from?  

Why is this whole process dependent on cold air entering a building and magically being heated and taking up moisture. The whole statement is a crock of rubbish.  In reality, in winter the external air is usually quite a lot drier than in summer.  Average air moisture contents in summer are around 12 g/m3 (grams per cubic metre - or about two teaspoons of water in every cubic metre of air.) In winter, moisture contents drop markedly - we've seen moisture contents (called the Absolute) of 5 g/m3.  So in reality, moisture in the air is a lot less than in summer.  The issue for homeowners is quite simple - if the temperature of the building fabric drops below dew point, condensation can form.  Now this is where the PCA get it even more wildly wrong:  They state that moist air comes into contact with cold surfaces, walls, windows etc and forms condensation.  They do NOT tell you that warm air, containing water AS A GAS - is DIFFUSING through the fabric - whether its brick, cement, wood, gypsum - and very happily diffusing outwards to the dry air outside (water moves from areas of high 'vapour pressure' to areas of low VP - in other words from wet internal conditions to dry external conditions.  This gas then condenses as it passes through the walls of the building at a point where the wall is below dew point - effectively forming fog in the wall. THIS is what the PCA and damp wallys call rising damp - and if the wall is breathable, it simply EVAPORATES away. If damp wally has coated the wall alaready with gypsum, cement, tanking siloxane chemicals, and so on, that evaporation cannot take place and the wall gets wet - oh - so now we have a wet wall with 'rising damp'.  Solution 1) Let it Breathe, and 2) Warm it above the dew point, 3) Reduce the moisture content of the air in the house (stop breathing, install extractor fans in kitchens and bathrooms and USE THEM, light a fire, etc.

There's another totally hilarious statement on their page:

"Intermittent heating and cooling of the property can aggravate condensation problems, since it allows warm damp air to cool, reducing its capacity to hold water. Dew points are reduced allowing condensation to occur. When the air is reheated water is taken back into the air only to be deposited again when the air temperature drops again."

Erm... if you reduce the dew point, you lower the temperature at which condensation can form you bloody idiots. That means it's even harder for it to happen. Why do you state that dew points are reduced? What magical piece of science are you using to deduce that warming and cooling air has any effect on the dewpoint? I'll let this bunch of complete morons stew on this one for a bit - clearly their intelligence has been somewhat challenged.

You know what folks - the PCA are gradually taking the science from our website, turning it around, and trying to gain credibility by regurgitating it on their own site.  The problem is, you can't do this Mr Hodgson, if you don't actually understand a word of it. And you don't want to do you - all you want to do is screw the public by selling them chemicals they never needed - by diagnosing imaginary problems like rising damp that never existed - and by trying to create credibility for your moronic members by 'qualifying' them in injection damp proofing.  

And then there's their 'Piece de Resistance':

Other devices that may be considered are positive pressure condensation control units also known as Positive Input Ventilation (PIV) units. These take dryer air from roof spaces or lofts and mix this with air in the dwelling. This is done at a very low rate (below half an air change per hour) and has the effect of lowering total moisture content and removing moist air by natural leakage.

Oh Jesus... these guys are now sinking to the depths of stupidity.  So you are going to find dry air in a loft?  You morons.  The ONLY rising damp I have ever seen is the clouds in the sky.  That's because water DOES rise - water is the lighter of the gases in air - it will rise quicker than oxygen or nitrogen, as a gas, and ALWAYS accumulates in the loft space of a house. WHY do you think Building Regulations are so hot on ventilating loft spaces? Almost all the moisture created in a building will end up in the loft space if it hasn't condensed at source - which is why we see so many cases of roof damage in houses with a lot of insulation in the loft - people dont realise that water goes straight through the ceiling, and because of the insulation is usually quite warm, meets cold air in the loft, and rapidly reaches saturation level. The WORST thing you can do is to take that saturated water and push it back down into the house where you create yet more problems.  How do you remove moist air "By natural Leakage" Mr Hodgson? What the hell are you talking about here?  Oh, yes - I know - your PCA companies are importing vast numbers of cheap, crappy fan units and flogging them to the unsuspecting public at HUGE profits, thus replacing lost income from fraudulent damp proofing with income from crappy, useless ventilation that works the wrong way round. 

The photo below is a classic - it's a ventilation system installed by a PCA member company - the fan is a NUAIRE - and it had apparently been installed to reduce moisture in a cellar. They were taking external air into the cellar, blowing it around, and circulating it out again. The cellar was warm, the air outside was cold. So the ducting was like a giant dehumidifier. You can actually see the drops of condensation running all down the silver ducting in the picture and dribbling off it. All they did was to soak all the personal effects in the cellar, create a river of water on the floor, and rot all of the timber in the place. This crap was ripped out and replaced with a professionally designed RHL / Vapourflow unit that has steadily dried out the cellar since we discovered the Nuaire rubbish that had been installed.

I, and many others, are shaking our heads in disbelief at this crap.