What does damp in an old house mean, or even in a modern house?
What damp is what in an old house? Rising damp, hygroscopic salts, salt damp that show up as a damp patch or stained patch, penetrating damp, condensation. This is when a damp survey is needed from a qualified Property Care Association surveyor http://www.property-care.org
What is rising damp?
Rising damp is the upward movement of ground water through the walls of the building, this can be in internal and external walls. The water rises (capillary action) through the pores of brick and mortar etc and the height of rise is determined by the the continuous continuity of the pores, the smaller the pore size the greater the rise, and evaporation.
How high can rising damp rise?
This is one of the questions I mostly here whilst i’m carrying out a survey, most of the public seem to think the height is 1 meter. I’ve recorded rising damp to 2.3 meters on a wall that was covered with bonding internally, I have recorded rising damp on party walls to 1.8 meters and I generally find party walls have the highest height of rise. Rising damp also occurs on lime plastered walls despite what some of the green conservation people say, as they say lime breathes, of course it can’t stop rising damp it’s not a physical damp course.
Generally though rising damp is normally up to 900mm on my BRE Digest 245 results. I think the publics thoughts of rising damp only reaching 1 meter in height is simply because that is normally that height of which the salt resistant re-plastering is normally carried out to. Bre states that under 5% moisture in walls is ok?! I’ve found many walls with 5% free moisture and the skirting boards are rotten and infested with wood boring weevil with paint and paper peeling! What about the type and amount of hygroscopic salts? This isn’t included in BRE Digest 245 and I think this is very important as this paints the picture of how much free moisture percentage there is, how much hygroscopic salts percentage present , and if you carry out a test for salts and have a salt band with nitrates and chlorides present at 900mm you have the perfect test to prove rising damp is happening at that time and the percentage of hygroscopic salts and that particular type of salt e.g. nitrates and chlorides.
Remember salts move in solution these salts don’t just magically appear in the wall, if you have a hygroscopic salt band between 800mm- 900mm how did they get there? The only way they can get there is from rising damp, so when the anti damp specialists claim that rising damp doesn’t exist, how can that be…….. There is scientific evidence that proves rising damp exists……..
There is no scientific evidence that proves rising damp doesn’t exist!
The below pictures showing rising damp on the original lime rendered and plastered walls.
The below picture shows our technician cleaning the cavity as this has caused rising damp because the debris bridged the cavity on an original lime plastered wall.
What is hygroscopic salts- salt damp?
The below pictures show hygroscopic salt damp on a chimney, that was confused with a leaking roof.
Hygroscopic salts absorb moisture from the air, some salts will be more visible than others depending on the percentage of salts and what salt it is. The humidity will also play a role, if you have high relative humidity there will be more moisture available for the salts to absorb. If there has been long term rising damp normally there will be a salt band present, this may not be visible when the relative humidity is low but this would show up on a BRE Digest 245 test and salt analysis and will also on a damp meter. Normally nitrate and chloride salts will be present. The salt band is normally present at the height of rise, the evaporation zone.
Some salts become deliquescent, they are then in a liquid form and are mobile, i’ve seen salts become deliquescent around a chimney breast at 81% relative humidity, this leaves runs on the wall that look like the roof is leaking. This is often mistaken for a leaking roof or chimney.
Most efflorescent salts are sulphates, they indicate the passage of water through the material.
Penetrating damp is damp penetrating the building, normally this is from defects such as leaking guttering and defective flashing.
Condensation normally occurs between October and April and is generally caused by the internal living conditions. A balance between ventilation, heating and thermal performance of materials to control a condensation problem long term.
Contact Complete Preservation for a survey on 01225 769215