What is Rising Damp?

Rising Damp is a term coined by the British damp industry to help them sell chemicals. These people are members of a chemical industry association called the Property Care Association, or PCA for short. Their website is flashy, and deliberately, desperately tries to make them look professional. They even help their fraudulent con artist members to write blogs and websites which try to make themselves look like educated professionals, which none of them are. Year on year, their income is falling as people realise what a bunch of con artists they are. These people are out to con you out of as much money as they can for selling you useless chemical treatments for something that doesn't happen. Look at the map of the world where the rising damp search term appears.. Google proves that Rising Damp is a peculiarly English term - how come there is no rising damp in America, or France, or Germany, or Holland... erm... Con Job comes to mind..

Now then. What is it? It's not a TV series starring Leonard Rossiter either...The entire industry, and the con, rely on the fact that condensation is constantly occurring in building materials. When it does, water starts to form within the pore spaces of the materials. Being water, it dissolves any salts in those materials, and as it evaporates when conditions change, the salts are left at the surface. The con men of the PCA love this, because they use a protimeter - a conductivity meter, or what they lovingly call a Damp Meter - which measures conductivity and bleeps to say the wall is damp. It isn't - it's just conducting because the pins are sitting in slightly salty, therefore conductive wall. There might at some time have been a bit of condensation there, but it's long gone now, and the wall is dry - but salty. So now they try to flog you rising damp treatment for something that was never rising - it was just some interstitial condensation in the wall that evaporated when the wall warmed up a tad.

Now - let's look at the physics of this a bit more: The air around us contains three main gases - oxygen, nitrogen, and water - with a bit of carbon dioxide. All of these are quite happily swirling around us all the time. They also diffuse very happily through the building materials of your home - passing through brick and stone constantly. Everything contains water vapour - your furniture, books, the walls, carpets, floors - but nothing suffers from damp. Thats because the water is present as a gas - you cant see it, its not doing any damage. Water is the lightest of these gases - so it does actually rise - I guess you could say rising damp or rising water molecules - its why the clouds are up in the sky - water rises as a gas, and then meets very cold air at the limits of the atmosphere, cools down and condenses, and appears as water - clouds.

A diversion - just to explain just how small some of these molecules are - and how easy it is for oxygen, nitrogen and water to get through your walls. I make cider. Usually about 500 litres a year. One year, I decided that rather than spending lots of dosh on buying glass bottles, Id cheat and collect old plastic coke bottles. All the cider was lovingly filtered into the bottles and screwed tight. Everything went into the cellars and I left it to mature. Come the first Barbeque of the summer, out came last years cider, and everyone took a gulp of my best.... disgusting, oxidised vinegar. I rang a cider making mate who works for one of the big cider companies. He cracked up laughing: "Pete - you fell for the oldest trick in the book - why is coke so chockers with preservatives? All your cider oxidised within a week or two - oxygen diffused through the walls of the plastic bottles and killed the cider - its why we sell in glass bottles, and the cheap stuff in plastic is absolutely loaded with preservatives!"

So - air can get through your Dulux emulsion paints, Sandtex masonry paint, the gypsum plaster, and cement - through brick walls and stone - everything in its path has tiny holes which allow it to flow through quite happily. Cider is a liquid, bigger molecules, and cant get out of the bottles. As with the cider - there's a catch.

We measure moisture levels in the air as Relative Humidity (RH). The colder the air, the less water it can hold. So air at 10 degrees can hold about half the amount of water than it can at 20 degrees. Relative humidity is the measure of how much of the total water potential is present at a given temperature. If the RH at 10 degrees is 100% - the air is saturated. If you warm this air to 20 degrees, it will only be about 50% saturated, or the RH will be 50%.

But... there's another variable, called the Absolute.  And this is the most important.  Absolute, or Total Moisture Content, is the actual amount, in grammes, of water in a cubic metre of air.  Dry air should contain about 5 to 7 grammes / m3.  Wet air can be anything up to about 15 g/m3.  For a given Absolute - lets say 7 grammes, the temp and RH can see saw from nothing to 100%.  So at 7 grammes, you can have an RH of 10% or 100%.  At say 95% a lot of folks would say your house was wet - it isnt - its quite dry.  It just means that if the RH reaches 100%, the TEMPERATURE at which it is 100% is known as the Dew Point.  That in turn means that condensation starts to form within the building fabric given those conditions.  Obviously the lower the absolute, the less chance there is of problems. 

Remember the clouds? Water gas cools down, and when it gets cold enough, it turns into liquid water. So if you take our 100% saturated water at 10 degrees and cool it to 9 degrees, its going to turn into water. If it happens to be inside your brick walls at the time, they are going to get wet. A bit like fog forming in the wall.

That, ladies and gentlemen, is what this massive con industry, the damp industry, is all about. Moisture, within walls, condensing as the walls get a bit cooler. Warm them up, and the water goes away again.

Or does it? Mr Damp Wally has for years been "remove the plaster to a metre high and replace with tanking slurry and damp proofing and salt inhibiting toxic chemical soup with some gypsum plaster over the top to make your toxic room nice again" And Wally Builder for years has been "we'll rake out those walls of yours and re-point them in nice cement Mrs Jones - it'll waterproof those walls and make them look really nice - even if we do destroy the bricks with angle grinders into the bargain" So - the walls are now wet because they are cold at the bottom - near the ground, where its normally colder - but theres Wally Slurry all over the walls turning them into a swimming pool, and Wally pointing on the walls, with or without Wally cement render.

So your wall is now a swimming pool, plus or minus toxic chemical injection holes. The problem is - your nice wet wall can't dry out, because the water liquid molecules are much bigger than the gas, and they are sitting in Wally Damp Mans swimming pool. Your Wall. How do we get them out? Strip Wallys cement from the walls, inside and out, and sit back and watch a miracle - dry walls.

I love that advert with Alexandr Meerkat - SIMPLES !

This video shows just how much air can be trapped in a piece of rock - we use a vacuum chamber to submerge some rock, and watch the air being sucked out. Remember - if the rock is below dew point, these air bubbles will contain water- and that makes your wall wet..


Why do you see 'rising damp' problems on internal walls?

Good question! It's all to do with temperature. It stands to reason that internal walls will be a bit warmer than those on the outside. The one constant is that the BASE of internal walls, and the BASE of external walls, where they are in contact with the ground, will be roughly the same. Ground temperatures don't vary much, a little cooler in winter, but pretty constant.

Now then: Remember the lesson from above - the warmer air is, the more moisture it can contain. If internal walls are warmer, the pore spaces within that wall can contain more moisture, as a gas. So they do - it's a given. The problem arises when the base of the wall is cooler than the Calculated Dew point - that warm, moist air travels around in the internal wall, and finds a cooler zone - often under the stairs, in a cupboard, or just the party wall in the middle of the house, and simply condenses near the floor. It can evaporate when conditions change, and as it does so, brings salts from within the wall to the surface. That's why you often see salty, fluffy deposits on walls in sheltered spaces, nearly always at low level - where that condensation has slowly evaporated and left the salts behind. More often than not, when we test these areas for total moisture content, they are bone dry - condensation rarely sticks around if it can get out - it will only build up and make the wall damp if it is trapped by modern plasters like gypsum. If the wall is lime plastered, nothing happens - it'll be dry. The same thing applies to exposed areas like bay windows. That bit of wall underneath a bay window is always exposed to wind and cold. It's near the ground. It's a magnet for condensation.

Nothing to do with the Property Care Associations favourite term - rising damp. The same thing happens - moisture as a gas in the wall, condenses, and then tries to evaporate. If the wall is nicely pointed in lime, not cement rendered, and lime plastered, it won't get wet. If everything is cement, moisture builds up and plaster, and even brickwork, will blow and spall. Result - a wet wall, a cold area, rotting timber, everything you don't want in your home. And all because of gypsum and cement. And nothing to do with a mythical lake of water just itching to bubble up into your walls. SIMPLES!

Damp and Condensation
A great book:

The definitive book on the fraud of rising damp, by well known Telegraph columnist, Jeff Howell:

And to measure the humidity in your home....

... You need one of these magic gadgets.  Keep it handy, move from room to room.  If you see humidity over 55%, you know you have a possible problem - not Rising Damp as the damp industry or your local PCA 'surveyor' will tell you - but condensation.  Press the button, and it displays Dew Point - the temperature that building fabric needs to be for condensation to start.  Armed with this, you will start to inform yourself about where and why damp may be occurring.  If you have questions for us about damp problems, we need to know what levels of moisture are in the house - this is what you need.

This particular model is new - it records temp, rh, and more importantly dew point:

There is a cheaper version that will sit on your table - but it doesnt calculate dew point, which is that magic temperature we need to know about to see where condensation might be starting within your walls:

If you have one of these, we still need to download a little humidity calculator online, to convert temp/rh into absolute, and dew point. They're really good little bits of kit though, and make you aware of whether the air in your house is too damp.

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