Water in cavity wall

January 1, 2015
Ceiling mould from water leaks

Relative Humidity HygrometerSummary: Find out how to diagnose and fix damp issues in your cavity walls and what problems these could be causing in your home.

One of the best ways of preventing damp travelling through the walls of a property and affecting the internal surface of the facing walls within your house is to build with a cavity however in some cases this itself can actually cause cavity wall damp issues.

Below is a list of ways a cavity can be compromised and allow damp through to the inside as well as a suggested fix for each issue.

If you would like some additional expert advice please call Property Repair Systems on 80, free of charge and no obligations involved.

Testing for Potential Damp Issues

Initially it is a good idea to firstly establish if you do indeed have cavity wall damp. There are two different ways of checking this:

  • Back of Hand - You can use the back of your hand and feel for damp, obviously not the most accurate of measurements but can in serious damp cases indicate issues with little, if any, initial expense.
  • Damp Meter - For a more accurate measurement you can purchase what's called a damp meter. There are two different types of damp meter, a Relative Humidity Meter or Hygrometer (these measure the amount of moisture in the air within a room space) and a Damp Testing Meter (these can be used to test the damp within actual materials such as plaster, timber or brick). NOTE: a Damp Meter will give you an indication of damp percentage, if any, and a good basis to establish any damp issues you may have but for an accurate reading laboratory testing is required. Damp Meters can be purchased from many of the DIY stores but

Good Example of Clear Damp Proof CourseDamp Testing Meter

Relative Humidity Hygrometer

DPC Covered by External Ground

Issue: DPC Covered by External Ground - The original damp proof course added when the property was constructed could possibly be bridged or covered. A damp proof course has to be a minimum of 6 inches or 150mm above the ground. This means in essence that on the outside of your property there maybe a section of high ground (sloping ground or a garden) or a newly built structure that is now butting up to your property e.g. a set of steps or a conservatory/outbuilding, that is now bridging the gap above and below the original damp proof course and providing any damp or moisture a direct route around the damp proof course and up into the external wall.

In the majority of cases a decent, clear cavity should stop any cavity wall damp or moisture penetrating into the inside wall but in the odd instance, the moisture can travel up the wall and meet a connecting medium such as a wall tie and gain access to the inside wall.

Good Example of Clear Damp Proof Course

Fix - To cure this issue you essentially have several options. The ideal fix is to clear the bridging structure e.g. dig back the garden and leave a gap between it and the external wall exposing the damp proof course, remove the sloping ground or remove the conservatory or adjoining structure. In the case of the latter two items (conservatory or joining structure) this may not be possible, especially if you have just spent £20, 000 on building the conservatory. If this is the case then this is quite a sizeable mistake on the builders part.

In the case that you are unable to clear the obstruction the best and easiest fix is to add a new damp proof course. There are quite a few products on the market today that enable you to DIY it quite quickly and easily such as Permagard or Twistfix. One that we have used on several occasions and found to give great results is UltraCure DPC Cream . Find out more about Damp Proof Injection and Damp Proof Courses in our DIY project.

Worst Case Scenario - Poor Cavity voidBridged Cavity or Filled with Rubbish

Issue: Bridged Cavity or Filled with Rubbish - The cavity void itself has been filled with rubbish and debris such as broken pieces of brick, mortar spillage or sand that has been dropped during the construction stage. As we know, the main point of the cavity is to keep water and moisture away from the inner walls of a property. Any water or moisture that penetrates the outer wall, runs down the inside of the outer wall, hits the Damp Proof Course and then runs back out. The introduction of debris to the void then blocks the channels used by the moisture to leave and also gives it a direct route to the inner wall, creating cavity wall damp.

Worst Case Scenario - Poor Cavity void

Fix - As you may have already guessed, the only way to fix this is to clean the cavity out. To do this you will need to remove 1 or possibly 2 bricks at floor level or as close to floor level as possible. (NOTE: do not remove anymore than 2 bricks at a time. If you need to remove more than 2 bricks please consult with a surveyor or reliable builder). This may sound like a bit of a daunting task but it's quite easy (see our Replacing a Damaged Brick project for more information). Once you have removed your brick(s) you can then use a camera or mobile phone with a light to view the cavity to establish it's condition.

Wall Tie Positioned Between Mortar Joints in Internal Cavity WallFrom this you should be able to see its condition and any rubbish that may be there. You can remove the rubbish by hand (wear some sturdy gloves as there may be sharp objects in there) and where debris is out of reach, use a bar or scraping device to drag it back. For a fine clean, use an old vacuum cleaner to suck up any smaller objects. Once done you can now replace your bricks.

Wall Ties Dirty or Corroded

Issue: Dirty or Rusty Wall Ties - Another way that damp and marks can appear on inner walls and affect the surface is due to the wall ties that are used to tie walls together. In some situations wall ties can become dirty, normally mortar sitting on them created at the time of construction, or possibly condensation allowed to collect on them due to gaps in mortar, leaking roof, gaps around window sills etc. that allows moisture and cold air to enter the cavity (which is technically known as Interstitial Condensation) and collect on the tie and create a "cold bridge". This causes a difference in temperature around the affected area on the inner wall and create a cold spot. The cold spot then allows moisture to condense much more easily than in the surrounding areas. This usually appears in the form of damp or mould.

In some cases wall ties can become rusty and corroded (again normally due to long term exposure to moisture from gaps or leaks). The act of rusting then in most cases creates its own gap that in turn allows moisture and cold air to penetrate the cavity and produce a cold spot on the inner wall. This type of issue can usually be easily spotted as cracks can be seen in the external mortar between the bricks or stones.

Wall Tie Positioned Between Mortar Joints in Internal Cavity Wall

Fix - Again as with the fix for a Bridged Cavity, you may have already guessed that the only way to properly diagnose and fix this issue is to remove a brick and possibly replace the wall tie itself. Firstly using a metal detector (these can be hired from your local hire shop) locate the suspect wall tie on the outer wall, using the damp on the inner wall as a reference to the rough area. Once the tie's been located remove the brick that connects to the tie and inspect the condition of the wall tie. If the tie is dirty, clean it properly. If it needs replacing then see our Checking Wall Ties DIY Project.

Obvious Gap Around Pipe in Internal Cavity Wall Salt Neutraliser
Source: www.diydoctor.org.uk
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