Trying to solve condensation damp is the second most popular reason, for householders in solid wall homes, to consider having their outside walls thermally rendered or cladded . The most frequent question we are asked is how can external insulation possibly cure damp condensation problems when it is adding yet another layer to their wet walls ?
How Exterior Insulation Stops Condensation
Solid wall insulation systems cure condensation by moving the dew point of a wall from the internal plaster surface to the outside of the external insulation boards surface ie the coldest part of the newly clad wall is the outside and not the inner sections.
Condensation – wet patches on the plaster leading to black mould or white “furring” – only occurs as a result of warm moist internal air hitting a cold surface such as when showering and seeing the mirror and windows steam up.
What is happening is that the water vapour in the air condenses from a gas to liquid when it comes into contact with a surface whose temperature has dropped low enough to reach the “dew point ” . This is the point at which condensation thrives and the only real way to stop it is to increase the wall temperature sufficiently to allow the moisture to pass through the walls as vapour and escape to the outside.
What about Interstitial Sweating ?
This is when moisture becomes trapped in the inner core of the wall and cannot escape to the outside as quickly as it needs to and so builds up to a point where the vapour condenses to liquid and begins to wet the core of the wall. Unlike surface condensation this interstitial damp cannot be seen so is especially dangerous and harmfulto the structure of our homes.
All reputable outside cladding and rendering systems have been tested by the Government funded British Board of Agrement for suitability of use on the UK’s solid wall homes and as part of the thorough testing regime they are checked to ensure they breathe more than sufficiently to avoid trapping moisture in the wall behind the thermal boards.
Better than Standard
The system renders that THINC Wethertex use al perform far in excess of the British Test Standard. The testing authorities use what they call a Dynamic Sweep Gas test to determine breathability and on their scale a material needs to score 25 or below to not be harmful to a home’s structure. Our thermal renders measured 12.8 which is classed as being highly breathable for a cladding system and way in excess of minium standards.