This project is presented by Property Repair Systems
Summary: How to diagnose and deal with damp and cold spots in walls
Damp spots on internal walls together with mould growth and cold spots which attract condensation are an eternal problem facing house owners. Our series of Damp projects will answer most, if not all questions about damp in the home. Click here for advice on cold spots and damp on internal walls or single skin walls
Cold Single Leaf Wall problems
Defects to check and eliminate before re plastering or lining with an Air Gap Membrane. A surface thermometer and a 'damp meter' (Click here for help with Damp Meters) are useful tools for this diagnosis - if not available use the back of your hand to assess the relative warmth of one affected area to another unaffected area.
Wall ties dirty: Can cause damp spots to appear on the inside plaster, sometimes with 'salt' or black mould. (Click here for help)
Remedy - Use a metal detector to locate the ties on the outside, examine with a borescope and remove a brick or block from the wall and clean the ties.
Wall ties rusting: Can cause damp spots to appear on the inside plaster, sometimes with 'salt' or black mould. (Click here for help)
Remedy - Use a metal detector to locate the ties on the outside, examine with a borescope and if necessary fit replacement ties before isolating or removing the old ones,(see Check Wall Ties Project).
Poor cavity insulation job: Can cause cold spots on the inside plaster, sometimes with 'salt' or black mould.
Remedy - Try re-injection first, but if this is not successful remove a brick or block from the wall and check the cavity insulation.
Penetrating dampness: Due to poor 'pointing' (mortar in the joints between bricks or blocks), crumbling or cracked brick faces (spalling) or cracked or hollow render. Dampness that comes through the wall may bring 'salts' to the surface of the plaster and these 'salts' attract more moisture from the air. Remedy - rake out the joints and re-point with a soft mortar mix (6:1:1 sand/cement/lime) with a plasticiser additive in the mix (Renderproof) or hack off and re-render, again with a soft mix, but using SBR to bond the new render to the wall and the edges of the old render. Scratch well between coats and damp the wall well before and after rendering, to slow the drying process(reduces the risk of cracking). Click here for help)
Condensation: This forms on the coldest surfaces in a room and often grows 'black mould'.
Remedy - hack off all the plaster and fit an Air Gap Membrane, plus insulation (Click here for help
Damp course 'bridged' or covered by high ground, pathway, garden or abutting new structure, (e.g. conservatory, steps): the damp proof course must be a minimum of 6 inches (150mm) above outside ground level, in order to avoid rainwater splash up causing penetrating dampness.
Remedy - Remove the obstruction or inject a new damp proof course at the proper level (Click here for help)
Service fixing, pipe or wire penetrates the wall: pipes, wires, bolts and other fixtures that pass into the wall can carry moisture inside, which may emerge at that level or drip down and show elsewhere.
Remedy - Remove the obstruction, or carefully seal the entry point. Pipes and wires should always be routed to climb up the wall immediately before entering the duct or hole, to avoid channeling the water by gravity.
Water pipes concealed inside the wall: Usually heating or mains water, but can also be boxed in foul water pipes or cistern overflows in modified houses.
Remedy - Remove the boxing or a brick or block from the wall to expose the defect.
Indoor Walls - ground floor, a quick summary checklist:
Symptom - White, fluffy salts, plaster possibly 'blowing' off the wall - 'efflorescence' - you have a water source which needs to be found and eliminated. Use our Water Leak Checklist (click here for the Check List).
Symptom - Damp patches (at low level, right down to the skirting board) that come and go - you have 'hygroscopic' salts that are attracting moisture from the air.
Answer - You may have Rising Dampness, or your damp proof course may be 'bridged' by high outside ground, plaster on the inside or debris in the cavity (cavity walls only). Rectify any defects and if necessary inject Quick Cream at the correct level to form a new Damp Proof Course. The plaster will need replacement to our Specification. (Click here for help)
Symptom - Damp patches on or around chimney breasts - sometimes showing yellow or brown stains in wallpaper or paint - you have 'hygroscopic' chimney salts that are attracting moisture from the air, which may include tars and other chemicals from burning wood or coal.
Answer - These 'salts' are very difficult to hold back in the wall, even with the re plastering to our Specification carried out to perfection. We recommend using Mesh Membrane - a type of dry lining - to allow you to re plaster using normal, lightweight plaster, with no risk of further 'salting'. (Click here for help)
Products mentioned above:
Salt Neutraliser - A clear liquid used to neutralise 'salts' in render, plaster or masonry, either in an attempt to save otherwise sound plaster or as a preparation prior to re-plastering to our Specification. Apply two coats, wetting in between with fresh water.
Mesh Membrane - easy to install dimpled plastic 'air gap' dry lining membrane, supplied in rolls like wallpaper. Designed to cover damp or salty walls and provide a fresh surface for re plastering with a modern lightweight plaster (usually 'bonding').
Quick Cream - new, easy to install, cream damp proofing product - no pump required, no mess, no smell - includes injection nozzle extension. Designed to gently diffuse into the wall to form a water repellent layer - a 'damp proof course'(DPC). It is approved by the British Board of Agrèment - BBA Test Certificate No: 02/3961 - as used by the professionals. The BBA is a Government Approved organisation which has been testing building materials for over 30 years. Note - not all damp proofing materials have passed these tests - beware of cheap imitations).
All project content written and produced by Mike Edwards
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