Damp in the walls of buildings is a problem which has been around for years and many methods have been invented to try to find and solve damp. The most under used instrument is something called a Speedy calcium carbide meter which looks kind of crazy but give accurate results, quickly and easily while on site.
Why Use Speedy Calcium Carbide Meter Testing For Damp?
Dampness in walls if often present in older buildings and sometimes new buildings. Diagnosing the source of the damp and the correct solution can be difficult and is simply not something which can be diagnosed during a quick 20 minutes sales survey.
So, how can we test for damp in walls? The obvious way is to use a Protimeter type 2 pronged damp meter which is poked into the wall at various points. When these meters encounter moisture or salts they light up like Christmas trees and give a % moisture reading.
This all sounds great and nice and simple except for the absolute, irrefutable facts, that these types of damp meters are calibrated for wood not plaster; and they cannot tell the difference between salt and water.
This means that two pronged (protimeter style) damp meters cannot:
- Give an accurate % moisture reading. The number shown is MEANINGLESS on masonry except for showing a trend such as this bit of wall has more salt/water than this bit of wall. It is a trend only not an absolute figure.
- They cannot tell if a wall is damp! They are brilliant at telling when a wall is not damp or salt contaminated but this is not the same as telling if a wall is damp.
Why can’t the electric damp meter tell if a wall is damp? Well, when water enters a wall it will inevitably bring with it liquified salts that migrate to the surface of the wall. Once present, these salts stay in situ, possibly for ever, so any damp readings from a 2 pronged electric meter will react to this salt as if the wall is damp. It does not matter if your house was built in 1850, previously used as a cattle shed and the walls are full of salt. The electric damp meter will say it is damp. Sadly, the uninformed damp salesman may also tell the homeowner the wall is damp and recommend lots of useless works.
How To Test For Damp In Walls?
The solution to this problem is to use the methodology outlined by the BRE in their digest BRE245 entitled ‘Rising Damp in Walls’. This was produced way back in 2007 yet still many companies, including the big national firms, still do not follow the guidance.
This is where the ‘Speedy’ calcium carbide meter comes into play. This device requires drilling of a few holes into the wall to take a masonry sample. These samples are then quickly analysed on site to get a reading of the true moisture content found in the wall at that location. This figure is an absolute % of total moisture content.
Due to the salts which can contaminate walls it is very possible that a wall which looks damp and gives a high reading on a protimeter electric meter is actually totally dry when tested with the ‘Speedy’ meter.
This is why we say that before having any expensive damp works carried you should invest the £300 it costs to have a calcium carbide survey carried out on the wall. This simple process could save £££’s on unnecessary works.
When dampness is found in the walls then it is necessary to determine where this moisture is coming from. One of the obvious questions at this point may well be “is it coming down from above or up from below”? A simple way we have found to determine this is to carry out a salts analysis of the moisture in the walls. This test is performed on site and quickly tells is common groundwater salts are present in the sample or not. If no salt is present then we know that the water is coming from above. If salt is found then it may be that rising dampness is present in the wall.